home Understanding HF Skywave Propagation
For Radio Amateurs: Beginners and Advanced

By Doron Tal , 4X4XM

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↑ Table of contents

Practical Approach

Band Activity
DXview
Real-time QSOs on 11 bands

Current band conditions
PSKR
PSK-reports

Real-time HF propagation conditions at a glance

Real-time observations
Charts with propagation indices
Regional MUF and Solar indices


Recent
Recent Solar Events
RSG repords in the last 3 days
Recent Space Weather Events
Forecasts

 Radio blackouts 

Tools & Applications

Theory-based tutorial

Introduction
1. HF radio propagation basics
2. Current propagation conditions
3. Real-time ham bands' activity
Skywave propagation basics
4. HF propagation modes
5. Impact of the Sun (preface)
6. The Ionosphere (preface)
Propagation factors & conditions
7. Ionosphere’s influence
  7.1 Ionospheric regions
  7.2 Skywave multi-refractions
  7.3 Long / mid range skywave
  7.4 Ionospheric conditions
  7.5 Critical frequencies: foF2, MUF, OWF, LUF
  7.6 NVIS propagation
  7.7 Greyline propagation

8. Regional HF conditions
  8.1 Ionosonde
  8.2 Ionogram
  8.3 Diurnal changes
  8.4 Seasonal phenomena
  8.5 Real-time propagation charts

9. Ionospheric dynamics
  9.1 Sporadic E (Es)
  9.2 Ionospheric "clouds" or "bubbles"
  9.3 Ionospheric disturbances: SID, TID, GRB

10. Total Electron Content (TEC)
11. Global HF conditions
  11.1 Banners & widgets
  11.2 Solar indices: SSN, Solar Flux
  11.3 Geomagnetic indices K, A, HPo
  11.4 Propagation indices

The Sun and space weather
12 Solar Phenomena
  12.1 Quiet Sun
  12.2 Active Sun
  12.3 Sunspots and Solar Flux
  12.4 Solar storms
  12.5 Solar cycle
  12.6 Predict solar flux
  12.7 Solar Alerts
13. Space weather
  13.1 Space weather explained
  13.2 Solar wind
  13.3 The Magnetosphere
  13.4 Geomagnetic activity
  13.5 Geomagnetic storms
  13.6 Space weather reports
  13.7 Predict space weather

14.  Radio blackouts 
15.  Summary 
References   * FAQ   * Sitemap   * Languages   * Visitors
 
* Index * Elpilog * Search

Introduction

↑   Chapter 1. HF radio propagation basics

What is radio?
The term "radio" comes from "radiation," which refers to electromagnetic (EM) energy moving as waves from one place to another.

Radio waves exhibit similar propagation characteristics as light waves.
For example, reflection, scattering, and diffraction influence radio waves, as shown in the following figure:

Multipath propagation characteristics

Multipath propagation characteristics


Radio waves (see below on the right side) are a part of the broader electromagnetic (EM) spectrum.

The EM Spectrum

The entire electromagnetic spectrum consists of various types of waves classified by their frequency and wavelength. The layout is from high to low frequency (short to long wavelength), consists of different regions, each with distinct features and applications.

Below see the radio spectrum bands from low to high frequency (long to short wavelength):

The Radio Spectrum Bands

In this project we focus on HF (shortwave) bands, which range from 3 to 30 MHz, propagating as skywaves over long distances between Earth's surface and the ionosphere.

The HF bands assigned to radio amateurs are:
  1. 160 m (1.800–2.000 MHz): Officially part of the MF range but also referred to as HF.
  2. 80 m 3.5–3.8 MHz (Region 1); 3.5–3.9 MHz (Region 3); up to 4.0 MHz (Region 2, the Americas).
  3. 60 m (5.3305–5.4069 MHz): Five 2.8 kHz USB channels; availability varies by country.
  4. 40 m (7.0–7.2 MHz) (Regions 1 & 3); up to 7.3 MHz (Region 2, the Americas).
  5. 30 m (10.100–10.150 MHz): WARC 1979; only CW and digital transmissions.
  6. 20 m (14.000–14.350 MHz): The most popular band.
  7. 17 m (18.068-18.168 MHz): WARC 1979.
  8. 15 m (21.000–21.450 MHz)
  9. 12 m (24.890–24.990 MHz): WARC 1979.
  10. 10 m (28.000–29.700 MHz) is the widest HF ham band.

The decline and comeback of skywave HF radio:

High Frequency (HF) radio experienced a decline due to the constantly changing nature of the ionosphere, which led to unresolved issues such as interference, fading, and limited bandwidth. The advent of satellites in the 1960s provided a more reliable, high-quality solution for long-distance communication, leading to HF radio's reduced usage. However, after 55 years of decline (1965–2020), HF communications via skywaves are making a comeback. The high costs and vulnerabilities of satellite-based global communications have renewed interest in HF radio. Technological advancements such as digital voice, automatic link establishment (ALE), and spread spectrum techniques have significantly improved the reliability and cost-effectiveness of HF communications. As a result, there is a growing interest in utilizing skywaves for long-distance communication.

The Advantages of skywave HF Radio over sattelites:
  • Skywaves travel longer distances and can reach places not covered by satellites.
  • No infrastructure required.
  • Low power wireless transmitters are sufficient over very long distances.
Key Points:
  • Essential for various sectors: Used in aviation, emergency services, maritime communication, and military operations for long-distance communication.
  • Crucial during emergencies: Vital for establishing communication and coordinating rescue efforts when traditional networks fail.

How does HF radio wave propagate?
See the chapter on HF Propagation Modes.

What are HF band conditions?

The term “HF band conditions” refers to the quality and reliability of HF radio signals transmitted within a specific band between two points on Earth via skywaves, influenced by the ionosphere’s dynamics.

This site explains the following key terms for HF propagation:

  1. Solar Indices (SSN and SFI): Measure the solar activity. Higher numbers suggest improved HF conditions.
  2. Geomagnetic Indices (A and K): Represent disturbances in the Earth’s magnetic field, affecting radio wave propagation.
  3. Space Weather: Conditions in space influenced by the sun and Earth’s magnetic field, affecting HF propagation.
  4. Radio Blackouts and X-ray Levels: Solar bursts of X-ray emissions can cause radio blackouts, impacting the travel of HF radio waves.
  5. Additional Factors, such as:
    1. How do time of day, season, and ionospheric state affect propagation conditions?
    2. How and why are skywaves used for long-range communication?
    3. What distinguishes different ionospheric regions, and how do they bend HF radio waves back to Earth?
    4. What are the characteristics of each HF amateur band?

See also the HF Propagation Overview page and the up-to-date FAQ list.

 

↑   Chapter 2. The current propagation conditions and short-term forecasts

How are HF conditions defined?
HF propagation conditions are defined by the maximum usable frequency (MUF), as determined by ionogramsionosonde measurements.

Can we forecast changes in HF conditions over the next hour?
Yes, we can forecast short-term changes in HF propagation based on real-time data.

What is the difference between forecasting and predicting HF conditions?
The main distinction between forecasting and prediction lies in the time frame. Forecasting refers to short-term estimations derived from real-time measurements, while prediction often involves longer-term projections based on historical patterns and statistical models.

HF propagation prediction is a method used to evaluate the quality of radio transmissions between specific locations on Earth via the ionosphere. Some general guidelines can help determine the best times and directions for band openings:

  1. Pre-dawn: 40 and 80 meters for dedicated hams.
  2. Sunrise: 20 meters opens for distances of 3,000–6,000 km.
  3. Late Morning: 10 and 15 meters may open for over 10,000 km.
  4. Afternoon: 20 meters may open to trans-equatorial routes.
  5. Evening: 40 meters offers opportunities for DX communication.
  6. Late Evening: 80 meters can remain open for extended communication.
  7. Night: 160 meters is ideal for those with large antennas.

Why do we need HF propagation forecasts?
HF propagation forecasts are essential due to the constantly changing nature of the ionosphere, which affects radio communications. By predicting key factors like the MUF, we can optimize frequency selection and timing for communication with specific locations. These forecasts are crucial for anticipating and mitigating disruptions caused by space weather events, such as solar flares and coronal mass ejections (CMEs), which can trigger geomagnetic storms.

In summary, HF propagation forecasts are necessary for:

  1. Selecting optimal communication frequencies and timing.
  2. Planning antenna systems effectively.
  3. Enhancing communication link reliability and coverage.


How has the forecasting of HF propagation conditions evolved over the last 30 years?
Remarkable advancements in space technology, software-defined radio (SDR), and the internet have revolutionized our understanding of radio wave propagation. Before the 1990s, propagation charts and reports were often published in amateur radio magazines. Today, real-time solar indices and computer programs provide more accurate, up-to-the-minute propagation data via online tools.


To assess current HF propagation conditions, we need to collect physical parameters and apply mathematical models, considering factors like time of day, season, solar activity, and ionospheric conditions.

Alternatively, real-time monitoring and analysis can provide immediate insights.

 

↑   Chapter 3. Real-time bands' conditions - Monitor and Analyze real-time ham activity worldwide

This chapter provides an overview of various methods, techniques, and tools for radio amateurs to understand HF propagation conditions.

Any of the following approaches could reveal the current propagation conditions:

  1. Use FT8 signals with PSKReporter to monitor and visualize real-time HF propagation.
  2. Monitor beacons to gauge signal strength and propagation paths.
  3. Compare signals using different antennas, or utilize various remote receivers, such as WebSDR, or KiwiSDR.
  4. Watch real-time charts, including DXview/DXmaps and DX-clusters, for up-to-date propagation information.
  5. Analyze real-time MUF maps and charts to understand the maximum usable frequency.
  6. Simulate current propagation conditions using offline and online applications and tools.

Using multiple methods will provide a better understanding of the propagation conditions, as no single method can offer all the necessary information. Please find below examples and explanations of these methodes.


↑   3.1 Use FT8 signals with PSKReporter to monitor and visualize real-time HF propagation.

In the past, scanning HF bands with analog receivers was time-consuming. Today, digital modes and waterfall displays allow quick analysis of band activity. FT8 facilitates real-time monitoring of active stations, while PSKReporter provides insights into band openings.

Below is a PSKReporter map from April 2, 2023:

PSKReporter demo
Signals received were analyzed by WSJT-X v2.6.1 software (running on a PC) reporting online to PSKReporter.
Receiving station: Malahite DSP v1.3 RX conected to K-180WLA 70cm diameter Magnetic Loop antenna (MLA)


↑   3.2 Track Global Beacons

It's a good idea to listen to NCDXF Beacon Network whenever you plan to hunt DX stations.

Eighteen worldwide beacons shown on the map below share five bands 20, 17, 15, 12 and 10 m and take it in terms.
All these stations use a standardized antenna and output power levels.


Eighteen beacons map

Click to see which beacon is now transmitting on what frequency?

All 18 beacons use the same five frequencies: 14.100, 18.110, 21.150, 24.930, and 28.200 MHz. It is recommended that you spend some time on one of these frequencies, listening to transmissions from all around the world. This option may indicate where the bands are now open.

The IDs of all the 18 stations are callsigns in CW and then a short carrier decreasing in four power levels: 100, 10, 1, and 0.1 Watts. If you can hear the 0.1W that means that propagation is really good or you're in a really low noise location. Put these frequencies in your receiver's memory channel and you'll be able to flick quickly between them.

While you're on 28 MHz tune up between 28.2 and 28.3. There's a lot of additional beacons all on their own frequencies operating full time.


↑   3.3 Real-time HF Bands Monitoring using Receivers accessed via internet: WebSDR / KiwiSDR

The majority of these stations offer waterfall and spectrum displays, as well as the option to record audio.

For example watch the entire LF–MF–HF spectrum at a glance using a  Wideband WebSDR at the University of Twente, Enschede, NL

entire shortwave spectrum

Alternatively, choose a remoted receiver from WebSDR or KiwiSDR lists, or the KiwiSDR Map (below):

KiwiSDR_map


↑   3.4 Real-time ham bands' activity using the internet

DXview, DXMaps, and DX clusters suggest open bands, as follows:

3.4.1 DXView—Real-time ham activity map designed by Jon Harder, NG0E.

DXview
Click on the map above to see the global radio ham activity for the previous 15 minutes on 11 ham bands (1.8–54 MHz).
Data is gathered from online sources: WSPRnet, Reverse Beacon Network (CW, FT4, FT8), and DX Cluster.
JavaScript is required to view the graphics.

 

3.4.2 DXMAPS—Real-time charts per band by Gabriel Sampol, EA6VQ

DXview
Click on the map to see the global radio ham activity.
Data collected online from various sources.

 

DX Clusters are nodes that gather information from radio amateurs about DX stations and/or real-time propagation conditions.

3.4.3 DXWatch alerts (using a filter) when a specific DX station is on the air.

3.4.4 DXZone is an amateur radio internet guide.

Reporters of digital modes:

3.4.5 PSK Reporter is an amateur radio signal-reporting and spotting network.

3.4.6 WSPR is a weak-signal radio communication protocol used for sending and receiving low-power transmissions to test propagation paths on the ham bands. Useful Links include: WSPRnet, WSPR Rocks, WSPR Live.


↑   3.5 Assess real-time band conditions using online propagation maps

Real-time forecasting of HF band conditions using maps on Maximum Usable Frequencies (MUF) optimizes long-distance communication, minimizes interference, and ensures reliable and efficient utilization of the HF spectrum.


↑   3.6 Simulate band conditions using online and offline applications and tools

Such apps and tools can simulate the current ionospheric condition and its effect on HF radio waves using mathematical models, data collected from recent solar activity, space weather reports, and real-time sensing of the ionosphere. All these topics are covered below.


Using multiple methods and tools is crucial for a better understanding of propagation conditions and accurate assessment. Find on this page real-time charts, space weather reports, solar-terrestrial data, apps, and tools that may help you plan your activity.

Skywave propagation basics

↑   Chapter 4. HF Propagation Modes

This chapter reviews the primary modes of high frequency (HF) radio propagation.

There are three main modes of HF Radio Propagation: LOS, Ground wave and Skywave

Propagation Modes
Illustration of HF Propagation Modes

1. LOS - Line of Sight propagation.

  • Line of Sight occurs when two stations are directly visible to each other.
  • Non-LOS-propagation could be any reflection by a conductive surface.
2. Ground wave or surface wave propagation
  • AM radio stations use ground wave propagation during the day.
  • Vertically polarized surface waves travel parallel to the Earth's surface and can cross the horizon.
  • Geologic features and RF absorption by the earth attenuate ground wave transmission.
  • Ground waves are effective below 1 MHz over salty seawater or conductive ground but are ineffective above 2 MHz.
3. Skywave


Currently this page does not cover the following propagation modes:
  • Aurora propagation: an Aurora event may create opportunities for QSOs on 50 MHz and 145 MHz (6 and 2 meters), while lower HF bands are disturbed;
  • Backscatter propagation;
  • Meteor Scatter propagation;
  • Moon Bounce (EME) propagation;
  • VHF-UHF-SHF "Scatter Propagation" due to Troposphere irregularities, offering communication between 160 km to 1600 km.
 

↑   Chapter 5. How does the sun affect radio communications?

Solar activity significantly influences the quality of skywave communications. The sun's activity affects the ionosphere, which is essential for reflecting radio waves back to Earth and enabling long-distance communication. Solar EUV radiation ionizes the atmosphere, creating the ionosphere that bounces HF radio waves, allowing them to propagate beyond the horizon.

Solar EUV create the ionosphere that enables propagation
Highlights:
  1. The ionosphere is a conducting region of plasma that refracts and reflects HF radio waves.
  2. Global and regional propagation conditions depend on the sun's position and orientation, i.e., time of day, season, and ionospheric state at geographical locations.
  3. High solar activity increases ionization in the ionosphere, resulting in better propagation conditions, especially in higher HF bands.
  4. The sunspot number and solar flux correlate with improved global propagation conditions.
  5. Solar storms can disrupt global communications.
All these topics are explained below.

   

↑ Chapter 6. The ionosphere (preface)

This chapter serves as an introduction, laying the basis for a deeper study of the ionosphere's influence in HF radio communication.

The term "ionosphere" refers to the upper region of the atmosphere.

The ionosphere is always changing, courtesy of NASA Goddard

The dance of radio waves within a vibrant airglow.
Solar storms intensify the ionosphere's beauty,
while Earth's weather below adds to the unique destination.

Earth's weather and space weather both affect the ionosphere, a spectacle of charged particles.

"Ionospheric clouds" move different speeds and directions, with irregularities in conductivity.

Ionosphere (Thermosphere) is part Earth's Atmosphere
The Thermosphere is characterized by very high temperatures ranging
from 550 to over 1300 degrees Kelvin, due to the solar EUV.

How does the ionosphere affect HF Radio Propagation?

The solar radiation generates free electrons in the ionosphere. The process is named "Ionization".


Generation of free electrons

HF radio waves from Earth to the ionosphere cause free electrons to oscillate and re-radiate, resulting in wave refraction with a refractive index similar to geometrical optics.


Refraction of radio waves in the ionosphere
The left two paths of signals demonstrate higher-frequency radio waves lost in space.

The refraction of radio waves in the ionosphere is characterized by their critical frequency. This is the highest frequency at which radio waves reflect back to Earth. Higher frequencies escape into space.

Read explanations in the next chapter.

Propagation Factors and Conditions

↑ Chapter 7. Influence of the ionosphere on radio propagation

The ionosphere refracts HF skywaves, enabling long-distance communication by multi-refractions.

Sub-topics: 7.1 Regions (layers)   7.2 Multi-refractions   7.3 Long / mid range skywave   7.4 Ionospheric conditions   7.5 Critical parameters   7.6 NVIS Propagation   7.7 Greyline Propagation


↑   7.1 Ionospheric regions

The D, E, and F "layers" are commonly used to depict the structure of the ionosphere, but this is not entirely accurate. Ionization exists throughout the ionosphere, with its level varying with altitude and fluctuating in time and geographical regions as a result of solar radiation. There is also a C region below them, which has low ionization levels that don't affect HF radio propagation. The term "region" is more appropriate.

It’s common to present the order of ionosphere regions affecting HF skywaves from the highest region downwards.

D-E-F regions Day-night
The ionospheric regions

  • The F-region, located between 180 and 600 km above the Earth, enables long-distance HF communication in the 3.5 to 30 MHz range.
  • This region consists H+, He+ (ionized Hydrogen and Helium ) has the highest free-electron density up to 1012 electrons per m3 excited by solar radiation 10-100 nano-meter EUV. It splits during the day into sub-regions F1 and F2. It slowly dissipates after sunset.
  • The E-region (90-150 km) dissipates a couple of hours after sunset.
  • This region consists O2+ (ionized Oxygen) up to ~1011 electrons per m3 excited by solar radiation 1–10 nano-meter EUV.
    During intense Sporadic E(Es) events (particularly near the equator) it sprodically reflects frequencies in the 50-144 MHz bands.
  • The D-region is the lowest at 50-90 km above ground. It is effective only during daytime, blocking radio frequencies below the LUF from reaching the higher E and F regions. This absorbing region dissipates at sunset.
  • This region is ionized by solar radiation (at 121.6 nanometers UVC of the Hydrogen spectral line), which ionizes Nitric Oxide, NO+ up to approximately 1010 electrons per m3. Bursts of solar flares (0.1–1 nm X-ray) may cause blackout events that can last minutes to hours.

These ionospheric regions differ in terms of gas compositions and free-electron densities:


An overview of the ionospheric regions

Layer
or
Region
Effective
height
Significance
charactristic
When Present Typical
MUF
MHz
Minimum
Electron
Density
Maximum
Electron
Density
Affected
by UV Solar
wavelength
Main
Ions
F  180-600 km HF Super Reflector Splits at daytime
into F1 and F2
15 - 30 1011/m3 1012/m3 10-100 nm H+ He+
E*   90-150 km Medium-Frequency and
Sporadic* VHF Reflector
Negligible at night 7 - 10 109/m3 1011/m3 1-10 nm O2+
D    48- 90 km Daytime Attenuation Daytime only 2 - 6 108/m3 109/m3 121.6 nm NO+
N2+ O2+
* See notes about Sproadic E-region.

The typical distribution of free electrons in the ionosphere

Plasma Density and height
The above graph is based on a review from U.C.Berkeley Bob Brown, NM7M (SK), Ph.D.

Free-electron densities fluctuate throughout the day and night, across seasons, and are influenced by various factors such as sunspots, solar cycle, geomagnetic storms, and lightning storms, all of which can affect radio propagation conditions.

Why does the density of free electrons increase sharply with height between 50 km and 250 km?

The density of free electrons is affected by the balance of two opposing processes: ionization and recombination (the capture of a free electron by a positive ion). The F-region gets most of the UV radiation compared to the lower E and D regions, while the rate of electron-ion recombination is much faster in the lowest D region (due to the higher gas density). As a result, the free-electron density of the high-set F-region (at noon) is significantly higher than that of the E and D regions.

At most, only one thousandth (1/1000) of the neutral atmosphere is ionized.


↑   7.2 Multi-refractions

The ionosphere bounces skywaves in multiple modes
Complex Propagation Modes
Complex modes: F Skip / 1F1E, E-F Ducted, F Chordal, E-F ocasional and sporadic E.
A modified version. The original figure is courtesy of the f.

The free electrons in the ionosphere refract radio waves as they move through the ionospheric regions, where the free-electron density gradually varies; numerous refractions are what create the frequency-dependent reflections of ionosphere skywaves.


↑   7.3 Long / mid range skywave

The figure below illustrates reflections from the F and E ionospheric regions at various angles

Ionosphere Reflection vs Angles
Long range skywave from F region (3 - 30 MHz)
Mid range skywave from E region (50 - 160 MHz)

The long-range skywave propagation typically uses a low transmission angle, which corresponds to a high incident angle
Transmission angle incident angle

The highest MUF occurs at the lowest transmission angle. This results in the longest range, meaning the transmitted ray is nearly horizontal.

As a rule of thumb, the MUF is approximately 3 times the foF2, as explained above: MUF factor = 1/cosθ.

See real-time worldwide 3000km MUF map


↑   7.4 Ionospheric conditions

The ionospheric physical conditions are: temperature distribution, free electron density, pressure, density, gas compositions, chemical reactions, and transport phenomena (horizontal and vertical winds), as illustrated below.

  • Temperatures distribution
    due to low or high solar flux
  • free electron density
  • ionic compositions.

  • Not shown on the right figure:
  • Gas pressure and density
  • gas compositions
  • chemical reactions
    of atomic ions with molecules
  • horizontal and vertical winds

Ionospheric physical conditions

The dynamics in the D-region are attributed to the reactions of the ions O+, N+, and NO+ with N2, O2, and NO.

The ionospheric conditions vary in 24-hour cycles, seasonal changes, solar activity, and geographical locations.

The next sub-chapter explains the critical frequencies that affect skywave propagation.


↑   7.5 The critical frequencies for HF radio propagation

The significant frequencies relevant for skywave propagation are foF2, MUF, OWF, and LUF.

7.5.1   The critical frequency (foF2) is the highest frequency below which a radio wave is reflected by the F2-region at vertical incidence, independent of transmitter power.

vertical incidence
Vertical reflection from F2-region (layer)

The critical frequency is depndent on the collision frequency of the free-electrons and their density:

Where fc is the critical frequency and Nmax is the electron density.

If the transmitted frequency is higher than the plasma frequency of the ionosphere, then the electrons cannot respond fast enough, and they are not able to re-radiate the signal.

For example, see recent foF2 measurements at various locations around Australia.

Statistically, between 2005 and 2007, the global average critical frequency (foF2) varied from 1.8 MHz to 11 MHz, with an average of 7.5 MHz.
The daily critical frequencies range from 6.8 MHz to 12 MHz.


7.5.2   The  Maximum Usable Frequency (MUF) is a fascinating concept in skywave propagation. It is the highest radio frequency reflected by the ionosphere at a given incident angle, independent of transmitter power.

MUF illustration
MUF illustration

    7.5.2.1 The MUF determines the conditions for radio wave propagation between specific locations.

    7.5.2.2 The MUF is calculated using the formula: MUF=foF2cosθ\text{MUF} = \frac{\text{foF2}}{\cos \theta} where foF2 is the critical frequency and θ is the incident angle.

    7.5.2.3 As a rule of thumb, the MUF is approximately 3-4 times the critical frequency.

    7.5.2.4 Ionosondes determine the critical frequency, which varies significantly based on location and time.
    Some general trends can be observed:

    7.5.2.5 Day vs. Night and Geographical Locations: The MUF varies with latitude and the day due to increased ionization from solar radiation. At night, the MUF decreases.

    SID effect
    MUF vs. latitude, courtesy of Australian Space Weather Service.

    This graph shows how the maximum usable frequency (MUF) for radio communications varies with geomagnetic latitude during the day and night. Day Hemisphere: The red curve (F2 layer) peaks around 18 degrees, forming an "equatorial anomaly." The blue curve (E layer) remains relatively flat. Night Hemisphere: The red curve shows a "mid-latitude trough" around 60 degrees latitude. Gradually growing towards the equator. These variations are crucial for understanding radio wave propagation and planning telecommunications.

    7.5.2.6 Seasonal Variations: The MUF is higher in summer due to the sun being directly overhead and lower in winter.

    7.5.2.7 Solar Activity: High solar activity can increase the MUF by enhancing ionospheric ionization.


7.5.3   The  Optimum Working Frequency  (OWF) is usually 85% of the MUF.


7.5.4    Lowest Usable Frequency (LUF) is the frequency where signal strength rapidly decreases due to D-region absorption.

The LUF (also referred to as "absorption-limited frequency" (ALF) or FL) is a soft frequency limit, unlike the ionospheric skip MUF. Transmitter power can overcome some absorption effects, which affect the LUF. A ray at a frequency lower than the LUF is absorbed in the D layer.

Absorption

Why does the LUF depend mainly on the D region?
Below the D region, the free electron density is negligible for absorption. Above the D region, there are fewer neutral atoms, so the E and F regions absorb far less than the D layer.

Why is there no global average for the LUF?
The Lowest Usable Frequency (LUF) varies significantly due to several factors, making it challenging to establish a global average. Here are the key reasons:

    7.5.4.1 Day vs. Night:
    During the day, the LUF is higher because of increased D-layer absorption caused by solar radiation. At night, the ionosphere becomes less ionized, leading to a lower LUF.

    7.5.4.2 Geographical Location: The LUF varies with latitude. For instance, the equatorial regions experience different ionospheric conditions compared to the polar zones.

    7.5.4.3 Seasonal Variations: The LUF is higher in the summer due to increased solar activity and lower in the winter.

    7.5.4.4 Solar Activity: Periods of high solar activity, such as solar flares, can increase the LUF by enhancing ionospheric absorption.
    Unexpected solar flares and solar particle events can also cause blackouts if the LUF exceeds the Maximum Usable Frequency (MUF).

Understanding these variations is crucial for effective HF radio communication, as it helps in selecting the optimal frequency for transmission.


↑   7.6 NVIS Propagation

NVIS - Near Vertical Incidence Skywave is a unique communication mode using skywaves directed almost vertically.

NVIS provides the solution for the dead zone (between groundwave and skip). It is the only solution for communication coverage in hilly and/or jungle areas over short distances of a few hundred kilometers.

NVIS
An illustration: How NVIS provides communications within a hilly area.
  • Typical operating frequencies are 2-4 MHz at night and 4-8 MHz during day.
  • NVIS requires suitable antennas (like a low dipole at hight of 0.1-0.25 wavelengths) to improve vertical radiation and reduce lower-angle radiation, contrary to what is customary for long-range communication.
  • NVIS offers enhanced resistance to fading (constant signal level), and minimal attenuation, making it suitable for low transmit power levels and omnidirectional coverage, allowing flexibility in setup and placement.
  • To avoid skip zones on 40 m band use NVIS when f0F2 is higher than 8.5 MHz. Switch to 80 m if the day is on the downward slope. Optimize antenna radiation pattern for the desired takeoff angle. Optimum NVIS height for horizontal dipoles: 0.18–0.22λ for TX and 0.16λ for RX. courtesy of Chris, N6CTA.

The NVIS map shows the recent global distribution of critical frequency (foF2).


↑   7.7 Greyline Propagation?

The greyline is a narrow band around the Earth that separates day and night.
Improved long-distance communications are possible on the lower HF bands for a brief period at dawn and dusk.

Why is radio propagation better along the greyline?

The absorbing D region is gone, but the reflecting F-region remains. This is because the F-region receives sunlight while the D-region does not.
Note: Because of the denser air at lower altitudes, the D-region dissolves before sunset, and ion recombination is faster.

Greyline illustration
The height of the F and D regions
is exaggerated in comparison to Earth dimensions.
  Greyline map
An example of a grey-line map

Some radio operators use specialized greyline map to predict when the grey line will pass over their location, as well as the best frequencies and modes of propagation to apply at that time. Overall, greyline propagation is a fascinating and useful phenomenon that has the potential to open up exciting opportunities for long-distance radio communication.


 

↑   Chapter 8. Regional HF Propagation Conditions

Regional HF propagation conditions provide a detailed picture of the conditions that individual operators are likely to experience.
The regional conditions are based on the observed values of foF2, MUF, and LUF between two locations.

Sub-topics:   8.1 Ionosondes   8.2 Ionograms   8.3 Diurnal changes   8.4 Seasonal phenomena   8.5 Current charts of MUF, foF2, and LUF


↑   8.1 Ionosonde

The ionosonde (invented in 1925) is an "HF radar" that emits short pulses of radio radiation into the ionosphere in order to determine optimal frequencies for HF communication.

How does it work?

Typical ionodonde modes are vertical and oblique:
Typical ionosonde
The ionosonde, also known as a chirpsounder, sweeps the HF range from 2 to 30 MHz. The transmitted (Tx) frequency increases at a rate of about 100 kHz per second and is digitally modulated in 25 kHz increments. Matching receivers (Rx) detect and analyze echo signals.

The ionosonde measures the time it takes for reflected pulses to arrive after being transmitted. The height (calculated from the time delay) is plotted versus frequencies. This recording, known as an ionogram, shows the plasma density distribution in ionospheric regions at various altitudes (48–600 km).

Every 15 minutes, real-time data from ionosonde stations throughout the world is reported via the internet.

Map of GIRO ionosonde stations

Some stations aren't always active, and significant regions of the globe are uncovered yet with ionosonde stations, as shown on the above map.

Readings of foF2 from several sites can be combined to build a propagation map for foF2.


↑   8.2 Ionogram

An ionogram is a visual representation of the height of the ionospheric reflection of a specific HF radio frequency.
Typical ionogram
A typical ionogram
E, F1 and F2 indicate ionospheric regions

Ionograms usually contain a dual representation:

  1. A series of (more or less) horizontal lines indicating the virtual height, at which the (amplitude modulated) pulse will be echoed as a function of the operating frequency;
  2. A curve in vertical direction representing the density of free-electrons per cubic centimeter, as a function of height.

↑   8.3 Day-night Cycle - Diurnal changes

The diurnal cycle on Earth occurs every 24 hours, with the sun affecting ionosphere characteristics. The E and F layers have larger electron densities during daylight, while the D layer disappears at night. The MUF and LUF rise with the sun and diminish after sunset.

 
Typical diurnal changes
Diurnal cycle

MUF - F region maximum usable frequency
OWF - optimum working frequency
EMUF - E region maximum usable frequency
LUF - lowest usable frequency

    References:
  • MUF, OWF, and LUF explained
  • Real-time MUF conditions

↑   8.4 Seasonal phenomena

Due to enhanced solar EUV radiation, free-electron densities are higher above Earth in summers than in winters, and near the equator than at the poles.


The dynamics of ionospheric regions near the equator and mid-latitudes

As a result, HF propagation conditions on the bands above 10 MHz are better in the summer and closer to the equator, whereas propagation conditions on the bands below 10 MHz are better in the winter and at high latitudes.


↑   8.5 Near real-time charts

    See below eight online charts of propagation conditions, all based on recent ionosonde measurements:
  1. Greyline chart with some regional propagation indices updated every 3 hours; Provided by N0NBH
  2. MUF 3000 Km map - information about HF propagation conditions at a glance
    provided by KC2G updated every 15 minutes | There is also an animated version.
  3. NVIS Map shows wolrdwide distribution of foF2 provided by KC2G updated every 15 minutes
  4. The next 3 NVIS maps are provided by the Australian Space Waether Forecast Center (ASWFC) updated every 15 minutes
  5. Chart of NVIS (foF2) ASWFC
  6. Chart of T index foF2 ASWFC
  7. Chart of foF2 Anomaly compared to the monthly median ASWFC
  8. Chart of recent foF2 measurements at various locations of Australia, New Zealand and East Antarctica ASWFC
  9. Chart of LUF ASWFC


↑     Greyline (Grayline) map showing near real-time propagation conditions; MUF values from selected regions and a few solar and geomagnetic indices—updated every 3 hours (by Paul L Herrman, N0NBH).
Solar indices and Regional MUF
It shows day-night, 13 local MUF reports, and the Global Indices: SFI, SN, A&K indices, 30.4 nm, Geomag, Sig Noise.

↑    Real-time MUF 3000 Km Propagation Map updated every 15 minutes

This map was developed between 2018 and 2021 to assist radio amateurs in finding the best times and frequencies for contacts by displaying HF propagation conditions at a glance.

  • This map shows the estimated MUF, calculated from ionograms.
  • A radio path of 3,000 Km is being considered for unification.

How to use this map? ↑

The colored regions of this map, which are rebounded by iso-frequency contours, illustrate the Maximum Usable Frequency that is expected to bounce off of the ionosphere on a 3000 Km path. The grey line position is also included.

The ham bands are designated by iso-frequency contours: 5.3, 7, 10.1, 14, 18, 21, 24.8, and 28 Mhz.
For example, if a given area on the map is greenish and lies between the contours labeled "10" and "14," the MUF in that location is around 12 MHz.

The raw data is MUF calculated from data collected by ionosondes, which are represented by numbered colored discs that show their location.
A number inside a disc indicates the calculated 3000km MUF from the critical ionospheric frequency, foF2. The information from the stations is compiled by Mirrion 2 and GIRO, and processed by the International Reference Ionosphere (IRI) model (produced by a joint task group of COSPAR and URSI.

The MUF along a path between any two locations shows the possibility of long-hop DX between those points on a given band.
For example, if the MUF is 12MHz, then 30 meters band and longer will work, but 20 meters band and shorter won't.
For long multi-hop paths, the worst MUF anywhere on the path is what matters. For single-hop paths shorter than 3000 Km, the usable frequency will be less than the indicated MUF. As one gets closer to vertical, i.e., NVIS, the usable frequency drops to the Critical ionospheric frequency, foF2 (as shown in the next map).

Additional Notes:

  1. The accuracy is insufficient for professional radio services because:
    1. Inaccuracy results from the limited coverage of radio stations. Therefore, the map is based on data interpolation. The algorithm aims to find the MUF (or FoF2) at scattered points globally, but achieving accurate extrapolation from few data points is challenging. The guessing process is better in areas close to measurement stations, but uncertainty increases in distant areas.
    2. Stations may provide inaccurate or disagreeing data, leading to peculiar results in an attempt to align measurements. Stations may go off-line or re-appear, causing unexpected changes in the model's global picture due to the limited number of data points initially used.
    3. Real-time ionosonde data sharing has been discontinued by countries like Russia, China, Japan, the US Space Force, and NOAA in recent years. Some ionosondes are only available through NOAA, and if GIRO outages occur, maps on this site may stop updating.
    4. There is uncertainty associated with predicting the ionosphere's state using vertical sounding data.
    5. Geomagnetic storms and blackouts, resulting from elevated X-ray flares and proton ejections, can significantly impact the accuracy of MUF estimation derived from vertical sounding data. This map does not refer to D-region absorption or to ionospheric noise. The propagation model is too simple.
    6. The effects of geomagnetic storms and blackouts are implicitly included in the results of ionograms. But it is impossible to predict band conditions for the next few hours. Geospace dynamic models are still being developed.
  2.  
  3. The "MUF(3000km)" project is the result of research and development by Andrew D Rodland - KC2G, which is based on an earlier work by Matt Smith - AF7TI. WWROF financing and data from ionosonde operators all over the world, provided by GIRO and NOAA made it feasible.
  4.  
  5. See Acknowledgments.
  6.  
  7. Read more about this open source project.
  8.  
  9. Read more about the open source software and models.
  10.    
  11. Roland Gafner, HB9VQQ, extended the static presentation with an animated map showing the last 24 hours in 15-minute steps. ↑

↑     NVIS real-time worldwide map (critical frequency: foF2) provided by Andrew D Rodland, KC2G updated every 15 minutes

foF2 map - if not displayed KC2G does not respond ***

The colored regions of this map, which are rebounded by iso-frequency contours, illustrate the critical frequency that is expected to bounce off of the ionosphere at near vertical angle. The ham bands (160, 80, 60, 40, 30 ,20m) are designated by iso-frequency contours: 1.8, 3.5, 5.3, 7, 10.1, and 14 Mhz.

foF2, as measured by ionosondes, is the raw data that powers the site.
Colored discs indicate the location of stations. A number inside each disc represents the critical frequency, foF2.


↑  Another NVIS map provided by the Australian Space Weather Service is updated every 15 minutes. It displays contours of the critical ionospheric frequency - foF2. There are a few differences between this map and the KC2G map, mainly due to the choice of frequencies for the contours. The KC2G map highlights ham bands. The following map, however, is designed for commercial use.
foF2 WW Map
Near real-time critical ionospheric frequency map
Click on the map to view the source page. There is further information.

↑   T Index Map - foF2 is provided by Australian Government Space Wheather Services

The T index is intended to correct inconsistencies between sunspot number and solar flux, as well as to account for geomagnetic storms that may affect the foF2.

This index can be any value, however it is usually limited to a range of -50 to 200. Low numbers suggest the usage of lower HF frequencies and vice versa.


↑  Current Anomaly Map of critical frequency, foF2, compared to the monthly median

foF2 WW Anomaly Map
Near real-time foF2 anomaly map
Click on the map to view the source page.

The plot above shows a near real-time foF2 anomaly map. The anomalies are calculated by subtracting the median foF2 for the last days from the currently observed foF2. The current foF2 and dataset are used to calculate the median foF2 the identical time of day and geographical attributes. The anomaly differences are in units of MHz. The regions in red indicate significantly lower frequencies compared to the last 30-day medians.
One may choose an animated display that shows changes in anomalies for the last 1-7 days.


↑ Recent foF2 measurements at various locations of Australia, New Zealand and East Antarctica

Current foF2 Plots
foF2 Plots courtesy of Australian Space Weather Forecasting Centre
Click on the map to view the source page.

↑ The recent LUF (ALF) chart provided by Australian Space Weather Alert System

During a solar flare, increased ionization in the D-region of the ionosphere can result in a fadeout.

The map below shows the LUF for 1500 km HF circuits. If the frequency you wish to use is lower than the LUF, then communication is unlikely; if it is higher than the LUF, then communication is possible.

For short circuits compared with 1500 km, the LUF values are likely to be too high, but communications will still be possible at slightly lower frequencies. For much longer circuits, slightly higher frequencies than the suggested LUF can still be affected by the fadeout.

The following real-time chart is event-driven and updates only when a flare of magnitude M1 or greater is observed.

Current LUF
LUF plot courtesy of Australian Space Weather Forecasting Centre
Click on the map to view the source page.
 

↑ Chapter 9. Ionospheric Dynamics

The upper atmosphere and ionosphere interact in a two-way nonlinear manner, known as the atmosphere-ionosphere system. The meteorological processes below influence the system, as do the solar and geomagnetic processes above. Gravity waves and planetary waves play significant roles in the energy and momentum budget of the thermosphere, while geomagnetic storms cause significant dynamical and thermal changes. Understanding this system requires a whole-hearted approach. This chapter discusses the effects of this complicated system on sky waves.

Sub-topics:   9.1 Sporadic E   9.2 Ionospheric "clouds" or "bubbles"   9.3 Ionospheric Disturbances


↑   9.1 Sporadic E

Sporadic E (Es) indicates occasional reflections from highly ionized "plasma clouds" in the lower E region.


Reflection from Sporadic E plasma cloud

Operators may use Es for making mid-range contacts on the VHF amateur bands: 50 MHz (6 m), 70 MHz (4 m), and 144 MHz (2 m).

Sporadic E Propagation in 2 minutes courtesy of Andrew McColm, VK3FS

Equatorial sporadic E (within ±10° of the geomagnetic equator) is a regular midday local time. At polar latitudes, however, sporadic E can accompany auroras and associated disturbed magnetic conditions and is called auroral E. At mid-latitudes, the Es propagation often supports occasional long-distance communication during the approximately 6 weeks centered on the summer solstice at VHF bands, which under normal conditions can only propagate by line-of-sight.


↑   9.2 Ionospheric Clouds

All the ionospheric regions consist of "plasma clouds" as illustrated below:

Ionospheric clouds

The moving plasma clouds or bubbles are traveling disturbances of electron density

How do "ionospheric clouds" affect HF propagation?

The dynamic ionosphere causes signal fading (QSB) over time. Small-scale irregularities in the ionosphere are observed at all levels, with periodic motions attributed to neutral atmospheric waves interacting with ionized components in the upper atmosphere. While understanding is limited, the research promises short-term changes.

Additionally the ionosphereic regions are disrupted by (1) The chaotic solar activity and (2) The tropospheric weather from far below.

What effect does tropospheric weather have on the ionosphere?

Storms, hurricanes, and strong wind patterns can all temporarily alter the TEC caused by EUV solar radiation.

In other words, the ionosphere and troposphere are coupled by a variety of mechanisms.

For instance, a lightning storm can cause electrodynamic interaction, as shown in the following figure.

The following figure illustrates electrodynamical coupling of the Troposphere with the Ionosphere:

TI-coupling

Ionospheric clouds due to Troposphere-Ionosphere coupling

 

Sprites - Transient Luminous Events (TLEs)
Sprites
The different forms of Transient Luminous Events. Credit: NOAA

There are other complex mechanisms that couple the troposphere to the ionosphere. We won't go into detail at this point.

In conclusion, "Ionospheric clouds" that develop as a result of the coupling between the troposphere and ionosphere may affect skywave HF propagation.


How are ionospheric clouds or bubbles detected?

The Digisonde Directogram was developed to identify ionospheric plasma irregularities.


Digisonde Directogram

It consists of multi-beam ionosondes, which measure echoes coming from various locations.
Seven ionosonde beams (one vertically and six diagonally) are used to generate the ionograms.
The end result is an extended ionogram of "plasma clouds" as they drift over a Digisonde station.


Sample directogram for Cachimbo station from 12 UT Oct 10 to 12 UT Oct 11, 2002.
Blue color means ionospheric motion from west to east.


↑   9.3 Ionospheric Disturbances

The ionospheric disturbances, SID, TID, GRB, are explained below.

9.3.1 "Sudden Ionospheric Disturbances" (SID) are any one of several ionospheric perturbations resulting from abnormally high ionization or plasma density in the D region of the ionosphere and caused by solar flares and/or solar particle events (SPE). The SID affects HF sky wave signal strengths, with lower frequencies being more heavily absorbed and resulting in a larger decrease in signal strength (see figure below).

SID effect
Fadeout signal strength vs. time, courtesy of Australian Space Weather Service

During a strong SID, the LUF will increase to a frequency higher than the MUF, thus closing the usable frequency window, an event called a fadeout or blackout.

The current fadeout (SWF: short-wave fadeout) event, if any, is shown below. Real-time chart provided by the Australian Space Weather Alert System.

Recent fadeout


9.3.2 "Traveling Ionospheric Disturbance" (TID) is a wave-like structure passing through the ionosphere that alters the altitude and angle of refraction of sky waves. TIDs travel horizontally at 5–10 km/minute, with varying phases, amplitudes, and angles of arrival. Some originate in auroral zones (high latitudes).

Probing traveling F region ionospheric disturbances

The Super Dual Auroral Radar Network (SuperDARN) is an international network of 35 HF radars (8 MHz–22 MHz) located in the northern and southern hemispheres.


SuperDARN site in Holmwood SDA, Saskatoon

The SuperDARN are designed to study F region Ionospheric dynamics, instability, disturbances and storms. The research covers geospace phenomena, including field-aligned currents, magnetic reconnection, and mesospheric winds. It tests theories of polar cap expansion and contraction under changing IMF conditions, observing large-scale responses to substorms. The collaboration includes various institutions.


9.3.3 "Cosmic Gamma-ray Bursts" (GRB) may also cause communications disturbances. Measurable effects are rarely observed.

On October 9, 2022, there was a cosmic gamma-ray burst that affected all ionospheric and stratospheric regions. These are intense explosions observed in distant galaxies, the brightest and most extreme events in the universe. NASA describes them as the most powerful class of explosions since the Big Bang. Afterglows are longer-lived and typically emitted at longer wavelengths.

Studies are being done on this phenomenon.

 

↑   Chapter 10. Total Electron Content (TEC)

What is TEC?
TEC is the total number of free electrons present along a path between two points.

Why is TEC important for HF propagation conditions?
TEC correlates with the critical frequency, foF2, and is therefore implemented in a variety of ionosphere models. Moreover, the total electron content can provide additional information about the structure and dynamics of the ionosphere. It can detect and monitor ionospheric disturbances, such as those caused by solar flares or geomagnetic storms.

Units: 1 TEC Unit (TECU) is the number of free electrons per square meter (x1016) for a shell height of 400 km directly above a certain point. Values in Earth’s atmosphere can range from a few to several hundred TEC units.

How is TEC measured?
Data is gathered from GPS receivers worldwide, observing carrier phase delays in radio signals from satellites above the ionosphere, often using GPS satellites.

The effect of Tropospheric weather:
The troposphere and ionosphere are separate atmospheric regions with distinct functions. However, they do interact through various processes. Tropospheric lightning may induce changes in total electron content and consequently affect HF propagation conditions. Thunderstorms can also worsen the signal-to-noise ratio, in particular in the lower HF bands; i.e., tropospheric weather may affect these conditions, especially in tropical regions. Thus, monitoring and modeling TEC patterns and variations allows us to better understand and prepare for the constantly changing atmospheric conditions.


The Ionosphere Monitoring and Prediction Center operated by the German Aerospace Center (DLR) provides near real-time TEC map:
*** If you don't see TEC Map it may be due to outage of the DLR website ***
Near real-time TEC map

An animated map courtesy of HB9VQQ demonstrates past TEC variations:

Solar EUV radiation, solar wind, CMEs, and atmospheric disturbances all contribute to TEC fluctuations, which vary with time, location, seasons, geomagnetic conditions, troposphere conditions, and the solar cycle. Data analysis may reveal qualitative patterns for spring, fall, summer, and winter solstices.

 

↑ Chapter 11. Global Propagation Conditions

Sub-topics:   11.1 Banners & Widgets   11.2 Solar Indices SN, SF   11.3 Geomagnetic Indices K, A and HPo   11.4 Propagation indices

Global HF propagation conditions are the overall factors, such as solar activity, the ionosphere's current condition, and in particular the average global ionization level of the F2-region that influence HF radio waves on a global scale.

However, regional conditions can vary significantly from global averages.


↑   11.1 Global conditions » Banners and Widgets

Banners and widgets are visual aids used to display real-time propagation conditions. They help radio operators quickly understand current global conditions and make informed decisions about their operations. The following banners and widgets were created by Paul L Herrman (N0NBH).

Ham bands global conditions
 

The Basic Solar indices
SFI, SN, A and K

SFI correlates with F2-region ionization (see below).
A and K indices indicate geomagnetic instability.

Solar-Terretrial Data, N0NBH
  Glossary of the Terms N0NBH, Paul L Herrman
Please use a landsape screen to wiew.
A-Index; good conditions A < 10K-Index: good conditions K < 3
X-Ray; Scales range from A0.0 to X9.9; affect D-region absorption
30.4 nm: Total Solar Radiation SEM (Solar EUV Monitor) wavelenth
Pf - Proton Flux Density | Ef - Electron Flux Density in the Solar Wind
Aurora indicates the ionization of the F-region in the polar zones
Bz: Magnetic field perpendicular to Earth's ecliptic plane SW: Solar Wind
 
Aur Lat - Aurora Latitude: Calculation from NOAA - estimate the lowest latitude auroa is observed
 
EsEU - Sporadic E over Europe. Updated every ½ hour.
EsNA - Sporadic E over North America. Updated every ½ hour.
EME Deg - Earth-Moon-Earth Degradation/attenuation. Updated every ½ hour.
 
MUF—Maximum Usable Frequency (MHz), updated every 15 minutes.
 
MS—Meteor Scatter Activity colored bar (updated every 1/4 hour).
 
GeoMag—Value calculated by using K-Index. Updated every 3 hours.
Sig Noise lvl—Background noise due to geomagnetic activity, calculated every ½ hour: S-units

Learn about the current solar images at four EUV wavelengths,
each associated with a different color of the sun disc
.


↑   11.2 - Global propagation conditions versus solar indices SSN and SFi Explained

The "Extreme Ultra Violet radiation" - EUV, creates the ionosphere, notably the F2-region. However EUV is completely absorbed by the inonosphere and therefore never reaches the ground. That is why ground-based devices cannot measure that EUV directly. Before the space age, scientists used two indirect markers to determine the ionization levels of the F2-region:

  1. SSN - Sunspot Number is a count of the number of dark spots seen on the sun.
    Higher SSN values correlate with improved conditions on 14 MHz band and above:.
  2. See the recent SSN values.

  3. SFI - Solar flux index refers to the intensity of solar radio emissions at 10.7 cm (2,800 MHz). Higher flux correlates with increased ionization levels of the E and F regions, enhancing HF radio propagation conditions.

Understanding the correlation between 10.7 cm solar flux and sunspots:

  1. Radio telescopes in Ottawa (February 14, 1947-May 31, 1991) and Penticton, British Columbia, have routinely reported solar flux density at 2,800 megahertz since June 1, 1991. Levels are determined every day at local noon (1700 GMT in Ottawa and 2000 GMT in Penticton) and then corrected to within a few percent for factors such as antenna gain, air absorption, bursts in progress, and background sky temperature.
  2. The solar flux is quoted in terms of SFU (Solar Flux Units) = 10-22 Watts per meter2 per Hz.
  3. The amount of solar radiation varies around the world. Even with correction factors added, it is difficult to obtain a consistent series of results. To overcome this, the reading from the Penticton Radio Observatory in British Columbia, Canada, is used as the benchmark. As a result, these numbers are extremely useful for predicting ionospheric radio propagation.
  4. The undisturbed solar surface, developing active regions, and short-lived enhancements above the daily level all contribute to 10.7 cm radio flux. Levels are determined and corrected to within a few percent.
  5. Sunspot Number records have been traced back to the 17th century. However, these records are open to subjective observation and interpretation. The 10.7 cm wavelength (2,800 MHz) also coincides with the daily number of sunspots. Both databases are interchangeable. The 10.7 cm Solar Flux data is more stable and reliable. See a comparison table between SSN and SFI.


↑   11.3 - The geomagnetic indices K, A, Kp, Ap, and HPo

Geomagnetic indices measure disturbances in Earth's magnetic field, which can disrupt HF propagation by increasing atmospheric noise and weakening radio signals. These indices are crucial for understanding the potential impacts on all communication systems, satellite operations, and even power grids.


K and A Local indices

K-index: This index represents short-term (3-hour) geomagnetic activity at a specific geomagnetic station. It quantifies disturbances in Earth’s horizontal magnetic field by comparing geomagnetic fluctuations, measured by a magnetometer, to a quiet day. The K-scale is logarithmic, allowing for a more manageable representation of the wide range of geomagnetic activity magnitudes.

A-index: This index averages K values to provide a linearized view of geomagnetic activity. It is important for predicting and understanding the effects of geomagnetic storms on HF communications.


Global Planetary indices

K and A indices measure local geomagnetic activity at a single observatory. A global average of these indices is calculated from 13 mid-latitude geomagnetic observatories, marked as Kp and Ap:

  • Kp is an average of K-indices from 13 geomagnetic observatories, giving a broad view of geomagnetic activity.
  • Ap represents the daily global geomagnetic activity, derived from the Kp index.

See a comparison table between K and A indices.


The HPo (GFZ) indices are less commonly referenced.
This higher time resolution can be crucial for predicting and mitigating the impacts of geomagnetic storms on various technologies.

The half-hourly Hp30 and hourly Hp60, developed at GFZ (German Research Center for Geosciences), offer improved time resolutions compared to the three-hourly Kp. Together with the linear versions Ap30 and Ap60, they are collectively known as the HPo index, providing near-real-time data from about 13 geomagnetic observatories.


↑   11.4 - Propagation indices

HF propagation indices are essential tools for amateur radio operators to evaluate and predict radio wave propagation conditions. The key indicators include the Maximum Usable Frequency (MUF), Lowest Usable Frequency (LUF), and ionospheric noise levels. These indicators are correlated with solar indices such as the Sunspot Number (SSN), Solar Flux Index (SFI), and X-ray flux, as well as geomagnetic indices like the A and Kp indices. Understanding all these parameters is crucial for accurately estimating HF propagation conditions.

Interpretation of the propagation indices

High solar indices SSN and SFI correlate with good HF propagation conditions.
ConditionsBADLowAverageGoodBetterBest
MUF< 15 MHz> 21 MHz> 24 MHz> 28 MHz> 50 MHz
SSN0255075100125150175200250
SFI6783102124148172196219240273
The source for this comparison between SSN and SFI.
 
High geomagnetic indices K and A indicate disturbed HF propagation conditions.
HF Propagation conditionsBestAveragePoorBAD
Geomagnetic activity index (log-scale)K0123456789
Geomagnetic activity index (linear)A 0  4  7  15 27 48 80132207400
The source for this comparison between K and A values.
The same applies for Kp and Ap planetary values.

Another type of interference


The recent Solar flares


Relayed by New Jersey Institute of Technology.
The observed indices of propagation conditions over the last 30 days, courtesy of QRZCQ
*** QRZCQ server is down ***
Please be aware of the various acronyms in the above chart
SF:=Flux index; SN:=Spot number; AI:=A index; KI:=Kp index; and XR:=X-Ray index.

In the next chapter, we discuss the solar phenomena.

The Sun and Space Weather

↑ Chapter 12 - Solar phenomena

Sub-topics: 12.1 Quiet sun  12.2 Active Sun 12.3 Sunspots and Solar Flux  12.4 Solar storms  12.5 Solar Cycle  12.6 Predict Solar Flux  12.7 Solar Alerts

Solar events are classified into two types: quiet and active. Both affect HF skywave propagation conditions.


↑   12.1 - Quiet sun

The sun emits Electromagnetic Radiation across a wide spectrum from Gama-rays to ELF (long radio waves).

Ionosphere formation is due to Solar EUV
The spectrum of solar electromagnetic radiation

The EUV (Extreme Ultra Violet) is the most significant solar emission affecting terrestrial radio communications.

see below the measured spectral lines of a "quiet Sun" at Extreme Ultra Violet - EUV:

Solar Spectrum SDO (Fig.11)
The EUV spectrum of the Sun, as measured by the SDO flown aboard a rocket in April 2008 (solar minimum between cycles 23 and 24)
 

Solar Spectra in the Extreme UV (10-120 nm) are capable of ionizing molecules (of earth ionosphere) by a single-step energy transfer.
This EUV light is emitted from the solar chromosphere courtesy of NASA, UCAR.

Peak (He II) EUV radiation at a wavelength of 30.4 nm is the most important solar emission contributing to half of the Ionospheric F-region ionization.

Lyman series-alpha Hydrogen-spectral-line at a wavelength of 121.6 nm ionizes Nitric Oxide (NO) at the D-region causing mostly absorption of HF bands below 10 MHz.


↑   12.2 - Active Sun

Solar activity is driven by the eleven-year periodic reversal of the sun's magnetic field. There is a helical dynamo in the sun's core and a chaotic dynamo near the surface.

    The main solar phenomena associated with HF radio propagation on Earth are:
  1. Sunspots (last from a few days to a few months); the number of spots varies in 11-year solar cycle (a deterministic chaos)
  2. 10.7 cm Solar Flux (a measurable indicator of solar activity)
  3. Flares (radiation bursts that last from tens of seconds to several hours)
  4. Solar wind propels energetic particles
  5. CME - Coronal mass ejections

All these affect space weather, as explained below.


↑   12.3 - Sunspots and Solar Flux

  • Sunspots are dark, cooler regions of the Sun's surface created by local magnetic activity.
  • These local magnetic fields inhibit heat transport, resulting in lower surface temperatures.
  • Sunspots can take on a variety of shapes, change size and last from a few hours to several months.
 
Two images of the Sun, that were taken at the same time (February 3, 2002)
by Solar and Heliospheric Observatory (SOHO) satellite
courtesy of European Space Agency and NASA.
Compare Sunspots and Flares
on the left: Sunspots in visible light             on the right Extreme Ultra Violet (EUV 30.4 nm)

Q. What is the reason for analyzing sunspots in both visible and ultraviolet light?

A. "Visible light" is what we see with our bare eyes. Magnetic disturbances are only detectable in EUV light.

The Current Solar Activity

Near real-time views of the Sun shown below were taken by SOHO telescope at various EUV wavelengths.
Brighter areas show higher levels of solar surface activity, i.e. higher Solar Flux Index.

Real-time SOHO images at EUV
EIT (Extreme ultraviolet Imaging Telescope)
images of the solar activity at several wavelengths
 
17.1nm
Fe IX/X
SOHO 17.1nm
19.5nm
Fe XII
SOHO 19.5nm
28.4nm
Fe XIV
SOHO 28.4nm
30.4nm
Helium II
SOHO 30.4nm
Solar Images courtesy of NASA, Solar Data Analysis Center
Click on a thumbnail to view a larger image (opens a new window).
Sometimes you may see the text "CCD Bakeout" instead of the images.
For a technical explanation, read NASA CCD Bakeout explanation.
 

The Extreme ultraviolet Imaging Telescope (EIT) is an instrument on the SOHO spacecraft, used to obtain high-resolution images of the solar corona. The EIT is sensitive to EUV light at different wavelengths: 17.1, 19.5, 28.4 nm produced by ionized Iron, and 30.4 nm produced by Helium. The four images show the intensity distribution at these wavelengths, originating in the solar chromosphere and transition region.

The average and local intensity may vary by orders of magnitude on time scales of minutes to hours (unpredictable solar flares), days to months (predictable solar rotation), and years to decades (predictable Solar Cycle).

The ionospheric free-electron density varies over similar magnitudes and time ranges as the EUV radiation.

 
The following video chronicles solar activity from Aug. 12 to Dec. 22, 2022, as captured by NASA’s Solar Dynamics Observatory (SDO). From its orbit in space around Earth, SDO has steadily imaged the Sun in 4K x 4K resolution for nearly 13 years. This information has enabled countless new discoveries about the workings of our closest star and how it influences the solar system.

133 Days on the Sun - courtesy of NASA Goddard

Historical charts of past events eSFI (Solar-flux-index) and eSSN(Sunspot-number) courtesy of Andrew D Rodland, KC2G.


↑   12.4 - Solar storms

For centuries, people have been observing sunspots without knowing what they are.

We now understand that these are symptoms of solar magnetic storms.

Solar storms consist of solar flares and Coronal Mass Ejections (CME)
 

(A) The "Solar Flares" are bursts of energeric radiation (X-ray and EUV, 1–10 Å) from the Sun.

Solar Flare
A Solar Flare courtesy of NOAA, May 2023
  1. Solar flares enhance the ionization of the ionosphere, specifically the D-region at 50-90 km altitude.
  2. The enhanced D-region absorbs HF radio, causing radio signals to fade out. These events are known as blackouts.
  3. Solar flares can last from tens of seconds to several hours.
  4. Solar flares classification: A, B, C, M, or X on a logarithmic scale.
  5. The D-Region absorption model is used as a guide to understand the possible fadeout events.

The current solar flare

(B) Charged Particle Events are CME, SPE, and SEP, explained as follows:

  1. Coronal mass ejections (CME) are huge flows of matter released from the sun with a larger mass compared to the solar wind.
    Solar storms may generate CME
    Image of coronal mass ejection (CME) captured by NASA and ESA's SOlar and Heliospheric Observatory (SOHO)
    Credit: NASA / GSFC / SOHO / ESA
  2.  
  3. Solar Particle Event (SPE) refer to protons ejected by the Sun during a solar flare or a Coronal Mass Ejection (CME).
  4.  
  5. Solar Energetic Particles (SEP) include electrons, protons, and alpha particles that are ejected from the Sun at high speeds.
    Reaching Earth they interact with the magnetosphere.
    Guided by the Earth's magnetic field, the charged particles are attracted by the north and south magnetic poles causing auroras.

Fadeouts and blackouts of radio communication occur when highly charged particles reach Earth.
Energetic protons penetrate all the way down to the D-region, boosting ionization levels close to the poles.

Polar Cap Absorption (PCA) occurs because enhanced ionization significantly increases the absorption of radio signals traveling through the region. In extreme cases, HF radio signal absorption levels may reach tens of decibels, which is enough to absorb the majority (if not all) of transpolar transmissions. These blackout events often last between 24 and 48 hours.


Sunspots, unlike flares and CMEs, are statistically predicted.
Sub-topic 12.5 discusses the Solar Cycle.
Sub-topic 12.6 presents long term prediction for Radio Flux at 10.7 cm.


↑   12.5 - Solar Cycle

Sunspots change in eleven year cycles. There are many sunspots during solar maximum and few during solar minimum.

Sunspot Number Progression since 1750
Solar Cycle Sunspot Number Progression
Source: The International Space Environment Service (ISES)
 

An animated overview of the Solar Cycle; published by NASA in May 2013

Solar magnetic flips are associated with solar maximum, when the number of sunspots is near its maximum, but it is often a gradual process that can take up to 18 months. The reversal will most likely take three to four months to complete.

The sunspot cycle begins when a sunspot appears on the sun's surface at roughly 30 degrees latitude. The formation zone then travels toward the equator. At its peak intensity, the sun's global magnetic field reverses its polar regions, as if the positive and negative ends of a magnet were flipped at each of the sun's poles.

There have been 24 (11-years) solar cycles since 1749. The magnetic field of the sun totally flipped every 11 years or so. In other words, the sun's north and south poles switched places. After two reversals (22 years), the solar magnetic field returns to its former orientation. This is known as "Hale cycle".

Understanding the complex interactions between solar magnetic fields, sunspots, and the solar cycle is crucial for comprehending the Sun's dynamic behavior and its impact on Earth, specifically HF propgation conditions.

The Current 25th Cycle began in 2020. The number of sunspots observed far exceeds predictions.

July 2024 marked the peak of Solar Cycle 25, with a monthly average sunspot number of 196.5, a new high. The last time this occurred was in December 2001. Despite predictions of a similar cycle size to previous cycles, Solar Cycle 25 exceeded these expectations.

Sunspot Number Progression
Sunspot Number Progression during Solar Cycles 24 and 25
The Recent Sunspot Number Progression
The recent Estimated International Sunspot Number (EISN)

Solar flux like sunspot number can be also used to show the observed and predicted Solar Cycle.
Sunspot Number Progression

  1. Solar Cycle Notable Events

  2. In the 19th century, more than 150 years ago, extreme events had been observed.

    The Carrington Event was the most intense geomagnetic storm, recorded on 1 to 2 September 1859 during solar cycle 10.
    SSN progression 1845-65
  3. Notable Events in the Recent Years

  4. The sun is getting angry; Should you really worry about solar flares? (August 2023)
    Misteries behind explosions on the Sun

    A glob of plasma and radiation that was blasted by an unexplained explosion on the sun's far side is expected to crash with Mars.
    According to researchers, if the solar storm strikes the Red Planet, it may cause weak UV auroras and even shred a portion of the Martian atmosphere.

    It missed us by 9 days (April 2022)
    9Days



  5. Comparison of the recent Solar Cycles by Jan Alvestad:
    The current solar cycle (25) is stronger than the previous cycle (24) but weaker than the three previous cycles (21-23)
    Comparison of Solar Cycles

  6. North-South Sunspot Asymmetries

  7. Previous research has found north-south asymmetries for solar activity. These data point to some decoupling between the two hemispheres during the evolution of the solar cycle, which is consistent with dynamo theories. So yet, only little data are available for the two hemispheres independently for the most important solar activity metric, sunspot numbers. Below see an example:
    Hemispheric Sunsopt Number 1950-2021 provided by SIDC - Solar Influences Data Analysis Center, Royal Observatory of Belgium

  8. Solar Cycle - radio emissions may indicate complex processes

  9. Multi-frequency (VHF-SHF) radio bursts superimposed on a persistent background characterize solar flares:
    Solar Radio Emission
    Picture Source: Patrick McCauley Mccauley.pi, CC BY-SA 4.0
  10. Solar flares are also characterized by radio wave radiation at different frequencies

  11. Different sunspot cycles can have different radio burst distributions at 245 MHz.
    That is to say that the sunspot cycles can vary and that they may not be considered identical.

    See an article covering Burst Comparisons, Probabilities, and Extreme Events:
    Solar Radio Burst Statistics in 8 Bands and Implications for Space Weather Effects
    by O. D. Giersch, J. Kennewell, M. Lynch (2017)
  12. Solar Interference with Terrestrial Services

  13. Solar radio bursts from the Sun can interfere with communication, radar, and navigation systems (e.g., GPS).
    The forecast of future solar events will be an underestimate of the true burst rate due to the deficiencies in the data archives.
    1 Solar radio emission as a disturbance of radio mobile networks (June 2022).
    2 What a Solar Flare *Sounds* Like When It Reaches Earth (2013)
    3 An analysis of solar noise outbursts and their application to space communication (1971)

↑   12.6 - Predict Solar Flux

The NOAA Space Weather Prediction Center predicts monthly sunspot number and 10.7 cm radio flux. The Sunspot Number indicates the number of sunspots visible on the solar surface, whereas the 10.7 cm Radio Flux quantifies the solar radio emission at a 2,800 MHz. A combination of observational data, analytical methods, and AI techniques contributes to predicting solar flux.

There are two recommended sources:
  1. Predicted sunspot number and Radio Flux at 10.7 cm are provided by NOAA / NWS Space Weather Prediction Center

    This is a multi-year (2022-2040) forecast of the monthly Sunspot Number and the monthly F10.7 cm radio flux.

    The Predicted values are based on the consensus of the Solar Cycle 24 Prediction Panel.

  2.  
  3. 27-Day Outlook of 10.7 cm Sun Radio Flux and the Earth Geomagnetic Indices
    prepared by the US Dept. of Commerce, NOAA, Space Weather Prediction Center.
  4. The 27-day Space Weather Outlook Table , issued Mondays by 1500 UTC, is a numerical forecast of three key solar-geophysical indices; the 10.7 cm solar radio flux, the planetary A index, and the largest daily K values. A complete summary of weekly activity and 27-day forecasts since 1997, plus an extensive descriptive, are online as the weekly.

  5. 3 Day Geomagnetic and Aurora Forecast SolarHam. Kevin, VE3EN
    SolarHam website relays data and images from various sources.

↑   12.7 - Solar Alerts

Extreme solar events may affect space weather and HF radio propagation.

Live Solar Alerts:
Solar Wind

Rice univ.
Flare scale

Current
ASWFC
Recent Flares

Greater than C8
Fadeout locations
Protons Alert

Proton flux
Proton energy
 

↑   Chapter 13. Space Weather

Space weather refers to events in space, beginning with solar storms that affect the geospace environment and induce geomagnetic storms.

Sub-topics :13.1 definitions and explanations, 13.2 Solar Wind, 13.3 Magnetosphere, 13.4 Geomagnetic activity, 13.5 Geomagnetic storms, 13.6 Space Weather Reports, 13.7 Space Weather Prediction

Why is Space Weather relevant to HF propagation?
HF communications can be disrupted by Solar Flares and Geomagnetic storms, which alter the ionosphere. Five major events are related to Space Weather:
  1. Solar Flares are sudden, intense bursts of radiation from the sun's surface. They can disrupt communications and navigation systems on Earth and pose risks to astronauts.
  2. Solar Wind is a continuous flow of charged particles, mainly electrons and protons, from the sun. It affects the entire solar system and can influence space weather around Earth.
  3. CMEs - Coronal Mass Ejections are massive bursts of solar wind and magnetic fields rising above the solar corona or being released into space. CMEs can cause significant geomagnetic storms when they collide with Earth's magnetosphere.
  4. The Magnetosphere acts as a shield against the solar wind. It deflects most of the charged particles, protecting our planet from harmful solar radiation.
  5. Geomagnetic storms are disturbances in Earth's magnetosphere caused by enhanced solar wind. They can lead to beautiful auroras but also disrupt power grids, satellites, and communication systems.
Space Weather Illustration
An illustration of the Space Weather environment
The Lagrange Mission was designed to monitor hazardous CMECoronal Mass Ejections headed toward Earth.
Credit: European Space Agency. Baker, CC BY-SA 3.0 IGO AGU - Advanced Earth and Space Science; Titles added by webmaster (4x4xm)
 

On the right side (of the above picture), you may see an illustration of the Magnetosphere, which protects Earth from Solar Wind. The magnetosphere is a part of a dynamic, interconnected system that responds to solar, planetary, and interstellar conditions. It is disturbed when solar wind interacts with the space environment surrounding Earth.

The Lagrange point L1 allows a sattelite to maintain a constant line with Earth as it orbits the Sun.


Animation of a satellite trapped at the L1 point
of the Sun-Earth-Moon gravitational system.
Published by Space Weather Live

↑   13.1 - Space Weather definitions and explanations

Space weather refers to variations in space conditions caused mostly by solar activity that affect the geospace environment and the Earth's magnetic field.

 

Other definitions:
  • Australian Space Weather Service: "Events beyond the Earth's atmosphere impact our technology and the near-Earth space environment."
  •  
  • Wikipedia: "A branch of space physics and aeronomy, or heliophysics, is concerned with the time-varying conditions within the Solar System, emphasizing the space surrounding the Earth."
  •  
  • Definition of Space Weather by INPE, Brazil: "There is no full agreement among all the members of the international communities on the definition of space weather. Therefore, they list the definitions of space weather according to some organizations."
 
  1. What kind of weather events occur in space?
  2. When are they likely to strike?
  3. Why doesn't space weather just torch us?
  4. What are the effects of space weather on Earth?
  5. How do scientists monitor space weather?
  6. Can individuals prepare for space weather events?
Space Weather Scales NOAA | pdf
The NOAA RSG scales describe three event types that have occurred or are expected, with numbered levels (0-5) for severity and possible effects. R0-5  Radio Blackouts
S0-5  Solar storms
G0-5  Geomagnetic storms

Reports of Space Weather Conditions

↑   13.2 - What is Solar Wind?

The solar wind is a stream of charged particles emitted by the sun's corona into outer space. These particles interact with Earth’s magnetosphere and magnetic field, significantly affecting skywave propagation and triggering auroras around the Earth’s poles.

Solar Wind
The illustration above depicts the solar wind reaching Earth’s magnetosphere. It shows how the solar wind rearranges the magnetosphere, compressing the magnetic field on the side facing the sun while elongating it on the opposite side.

The illustration above shows the solar wind reaching Earth’s magnetosphere. It demonstrates how the solar wind compresses the magnetic field on the side facing the sun while elongating it on the opposite side.

The solar wind can vary greatly in speed, density, temperature, composition, and interplanetary magnetic field (IMF). These variations are influenced by solar activity, such as coronal mass ejections (CMEs) or coronal holes. Although predicting exact changes in the solar wind is challenging, there is some correlation with sunspots and solar flares.

The “Interplanetary Magnetic Field (IMF)” is the magnetic field carried by the solar wind. It interacts with Earth’s magnetosphere, and when aligned with Earth’s magnetic field, it can cause magnetic reconnection events, leading to geomagnetic storms.

The solar wind can reach Earth between 20 to 30 minutes after a solar storm begins and up to four days later.


↑   13.3 - The Magnetosphere and Earth's Magnetic field

Earth’s magnetosphere is the region around the planet dominated by its magnetic field. It acts as a shield, protecting us from the harmful effects of solar wind and cosmic radiation.

Earth's Magnetosphere
The magnetosphere is a "magnetic bubble" that surrounds Earth.
Its shape depends on the solar wind and the orientation of the Earth’s magnetic field.
Earth's Magnetic field

Earth's Magnetic field—the geomagnetic field.

The orientation of the Earth’s magnetic field is composed of two variables: (1) the Earth's axis is tilted 23.5 degrees to the ecliptic plane, and (2) the Earth's magnetic field is tilted 11 degrees relative to the Earth's axis.

The geomagnetic conditions, influenced by solar activity, significantly impact the HF propagation conditions due to the Earth's magnetic field and the state of the surrounding magnetosphere.


↑   13.4 - Geomagnetic activity

Geomagnetic activity refers to the disturbances in Earth’s magnetic field caused by solar wind and other solar phenomena. These disturbances can range from minor fluctuations to major geomagnetic storms.


↑   13.5 - Geomagnetic storms affect HF propagation

Geomagnetic storms are significant disturbances in Earth’s magnetosphere caused by solar wind shock waves or coronal mass ejection (CME) from the Sun that disrupt HF communication and trigger auroras:

  1. Geomagnetic storms are more frequent during periods of high solar activity.
  2. Geomagnetic storms occur one to four days after a CME.
  3. These storms alter the normal conditions of the magnetosphere and ionosphere.
  4. Radio waves of certain frequencies may experience high absorption levels, leading to rapid fading events and unusual radio propagation paths.
  5. There are two main effects on radio communications: storms can reduce the MUF in equatorial regions, worsening conditions for HF bands, while increasing the MUF in polar regions, improving low VHF contacts.
  6. HF absorption levels are higher, especially in the lower bands near the equator, which can cause a complete fadeout of HF signals.

Illustration of geomagnetic storms—"auroras" as seen from earth close to the polar regions:


Public-domain photographs show electrical discharge in ionospheric regions near Earth's polar regions.

The correlation between geomagnetic storm G-scale, Kp and Ap indices, and HF propagation conditions is quite intricate.

The correlation between G-scale, Ap, Kp indices, and propagation conditions
Geomagnetic stormsG0-5G012345
 
Disturbance (3-h log. scale)Kp0123456789
Disturbance (24-h linear sacle)Ap 0  4  7  15 27 48 80132207400
 
HF Propagation conditions BestAveragePoor BAD

A geomagnetic storm has three phases: initial, main, and recovery. The initial phase involves an increase in the "Disturbance Storm Time" (Dst) index by 20 to 50 nano-Tesla (nT) in tens of minutes. The Dst index estimates the globally averaged change of the horizontal component of the Earth's magnetic field at the magnetic equator based on measurements from a few magnetometer stations. Dst is computed once per hour and reported in near-real-time.

What causes geomagnetic storms?

Solar magnetic storms trigger geomagnetic storms, which become more intense when the sun’s magnetic field reverses polarity approximately every 11 years. This process is associated with various solar phenomena, including sunspots, solar flares, and coronal mass ejections (CMEs).

A CME is a shock-wave of highly charged particles emitted by the sun.

When a CME enters the magnetosphere, it causes a Geomagnetic Storm

Major magnetic storms may block HF propagation (3–30 MHz) by modifying the distribution of free-electrons in the ionosphere.


↑   13.6 - Online Reports of Space Weather Conditions

Space weather reports may help to understand variations in HF propagation conditions.
  1. The current Solar Wind and Interplanetary Magnetic Field Rice Space Institute
  2. The recent 3 days of R-S-G graphs NOAA SWPC services
  3. The recent 7 days Kp index Europen Space Weather Service
  4. The recent 8 days K indices in the UK and the global Kp British Geogolocal Survey
 

↑ Current The solar wind affects ionospheric conditions and HF propagation.
The Rice Space Institute’s provides "real-time dials" showing the current solar wind (SW) and the interplanetary magnetic field as measured by ACE.


sw speed sw density sw pressure SW temperature
Speed x100 km per second Density of charged energetic particles per unit volume Pressure
The force per unit area required to stop the solar wind flow; nP = nano pascals
Proton's Temperature

Background color indications: no disruptions potential disruptions disruptions.

Real-time Interplanetary Magnetic Field (IMF) as measured by the ACE Magnetometer.
IMF magnitude IMF Clock IMF Azimuth IMF Convection
Nano TeslaPotential danger to high altitude aircraft in the polar regionsImpact on Magnetosphere InteractionsVoltage Across the Polar Cap x10 Kv

 
↑ Recent 3 days of Space Weather courtesy of NOAA SWPC
    RSG reports of three event types:
  1. R0-5  Radio blackouts caused by solar X-Ray flares
  2. S0-5  Solar storms characterized by charged particles flux
  3. G0-5  Geomagnetic storms that affect HF propagation
  3 days RSG
 

↑ Recent 7 days Kp index
provided by Europen Space Weather Service Network

 

↑ Recent 8 days of UK K indices and the global Kp
provided by British Geogolocal Survey

 


↑   13.7 - Space Weather Prediction and HF Propagation Forecasting

Space weather prediction is crucial for HF radio forecasting. By understanding solar-terrestrial interactions, radio operators can adjust frequencies for optimal communication.

Space observatories

Satellites play a crucial role in predicting space weather and its impact on HF radio propagation:
  1. ACE (Advanced Composition Explorer): Provides real-time data on solar wind and geomagnetic storms, giving up to an hour's advance warning of space weather events that can impact Earth. Located at the L1 Lagrange point, where Earth’s and Sun’s gravitational forces balance.
  2.  
  3. GOES (Geostationary Operational Environmental Satellites): Tracks solar flares and other space weather phenomena, aiding in timely alerts and mitigating potential impacts on HF propagation and space technology.
  4.  
  5. DSCOVR (Deep Space Climate Observatory): Monitors real-time solar wind, providing early warnings for geomagnetic storms.
  6.  
  7. SDO (Solar Dynamics Observatory): Delivers detailed images of the sun divided into four spectral bands.
  8.  
  9. SOHO (Solar and Heliospheric Observatory): Monitors solar activity and space weather.
  10.  
  11. STEREO (Solar and Terrestrial Relations Observatory): Consists of STEREO-A (Ahead) and STEREO-B (Behind), which orbit the Sun near the stable Lagrange Points L4 and L5 to provide a 3D view of solar phenomena from multiple perspectives.
  12.  
  13. The Parker Solar Probe significantly contributes to the prediction of space weather. By flying closer to the Sun than any previous spacecraft, it collects unprecedented data on the solar wind and the Sun’s corona.

Ground-based observatories

  1. Ionosondes: Measure the ionosphere’s electron density profile by transmitting radio waves and analyzing the returned signals. They help determine the ionospheric layers’ height and density, crucial for predicting HF radio wave propagation.
  2.  
  3. Magnetometers: Measure geomagnetic fluctuations, providing data on the Earth’s magnetic field. Near the equator, they help monitor geomagnetic storms and disturbances that can affect HF propagation by altering the ionosphere’s structure.
  4.  
  5. Radio telescopes: Detect solar radio emissions, which can indicate solar flares and other disturbances. By monitoring these emissions, scientists can predict space weather events that might impact HF radio communication.

Ground-based observatories, combined with satellite data, provide a comprehensive picture of space weather conditions affecting HF propagation.

 

↑ Chapter 14. Radio blackouts / fadeouts

Solar X-Ray flares cause radio blackouts.

Current and predicted fadeouts as reported by ASWFC
Flare alarm
HF fadeout

current
Fadeouts

Possible
fadeout
During a blackout event, the drop in signal heavily affects the lower HF bands:
SID effect
Fadeout signal strength vs. time, courtesy of Australian Space Weather Service


The correlation between band conditions, radio-blackout scale and solar-flare classification
Band conditionsBestAveragePoorBAD
Radio-blackout scaleR0R1R2R3R4R5
Solar  Flare  Class A  B  C MX


→ The recent solar flares.

→ The last remarkable radio blackout occurred on May 11, 2024.


Prediction Model

The D-Region Absorption Prediction (D-RAP) Model (by SWPC-NOAA) analyzes how solar phenomena affect HF radio communication, as illustrated below:


* Search the term "Blackout" at NOAA website.
 

↑ Chapter 15. Summary

Review of the practical techniques for forecasting radio amateur band propagation conditions:

  1. Utilize weak signal digital modes like FT8, JT65, or WSPR. These modes are designed to work well even when signal strengths are low, making them ideal for probing the ionosphere under less-than-ideal conditions.
  2.  
  3. PSKReporter can help you track where your signals are being received and how well they’re propagating. It’s a great way to get real-time feedback on your transmissions and adjust your strategy accordingly.
  4.  
  5. Smart F2 Layer Usage: Since F2 ionization can be unstable or limited, keep an eye on real-time MUF (Maximum Usable Frequency) maps. These maps can help you identify when and where the F2 layer is supporting higher frequency communications, allowing you to take advantage of brief openings.
  6.  
  7. Be Flexible: Conditions can change rapidly, so be prepared to switch bands or modes as needed. Monitoring tools like the Reverse Beacon Network or DX Cluster can provide valuable insights into current propagation conditions.
  8.  

Review of the tutorial aspects explained in the previous 14 chapters:

  1. HF radio is a form of electromagnetic radiation that travels as waves at the speed of light. HF radio waves can travel very long distances without the need for infrastructure like satellites or cables.
  2.  
  3. There are three main modes of HF radio propagation: line of sight (LOS), ground wave, and skywaves that involve wave reflections from the ionosphere.
  4.  
  5. The ionosphere enables propagation of HF radio over large distances. Solar radiation (EUV) forms the D, E, and F regions at heights from 48 to 600 kilometers above the Earth. The outermost F-region supports long-distance HF transmission (skywave). The inner D-region mostly absorbs the lower HF bands (1.8–10 MHz). Ionization during the day and dissipation at night affect all the HF bands, as well as the seasons and solar conditions, such as the 11-year sunspot cycle.
  6.  
  7. NVIS is a unique communication mode used for local coverage in hilly and/or jungle areas, over short distances (a few hundred kilometers).
  8.  
  9. The greyline refers to the Earth's twilight zone between day and night, that is considered a "sweet spot" for HF radio communications.
  10.  
  11. Forecasting HF propagation conditions is the process of predicting how radio waves will travel through the upper atmosphere. It may help in selecting communication frequencies, planning antenna systems, and optimizing coverage.
  12.  
  13. Real-time Band Conditions can be assessed using various methods, such as: monitoring band activity through DX clusters, using personal receivers, accessing remote receivers via internet (WebSDR or KiwiSDR), monitoring CW beacons, and watching real-time charts or maps. It's recommended to use a combination of tools to get a complete picture of propagation conditions.
  14.  
  15. The Solar EUV radiation ionizes the upper atmosphere, forming the ionosphere. The free electrons in the ionosphere bend and reflect radio waves back to Earth.
  16.  
  17. The amount of Solar emissions and the sun's position affect HF propagation conditions. Sunspot numbers and solar flux serve as indicators for assessing global propagation conditions. Higher solar activity improves propagation conditions, while solar storms can disrupt communications.
  18.  
  19. During the day four ionospheric regions are active. The D-region vanishes at sunset and the higher regions E and F dissipate at night.
    Ionospheric D-E-F Layers
  20.  
  21. Diurnal changes in the day-night cycle are due to the Earth's rotation around its axis, which causes periodical changes in the free-electron density of all regions.
  22.  
  23. The F-region is the dominant "reflector" of Skywaves. Higher electron density of the F2-region enables bauncing of higher frequencies.
    The effective range for communication is a function of the incident angle:
    incident angle
    and the MUF is affected by the free-electron density in the ionosphere:
  24.  
    Ionospheric electron density - typical profiles

    Day-night, and Solar Cycle Min/Max variations
    are based on 1987 research of Arthur D. Richmond

     
  25. Seasonal and diurnal phenomena: HF propagation conditions are better in the summer and closer to the equator. This is because direct solar radiation generates more free-electron in the summer and near the equator.
  26.  
  27. Local anomalies: The ionospheric regions are not homogeneous but rather composed of moving "plasma clouds." Nowadays, we can predict ham band conditions by probing these "clouds."
    PredictIonospheric clouds
  28.  
  29. Regional anomalies:
  30.  
  31. The critical frequency is an important characteristic that defines short wave propagation conditions. It correlates with Sunspot Number.
    The graph below illustrates variations in the critical frequency as a function of years and seasons.
    Correlation of SSN and Critical Frequencies and Time
    The critical frequency and Sunspot Number and Time, published by ASWFC
  32. The right vertical axis shows sunspot sumber represented in the graph by the redish line.

    The left vertical axis denotes critical frequency - the highest frequency reflected at noon at near vertical angles from the F2, F1, and E leyers.
    The F2 region has greater fluctuations in electron density compared to the F1 and E regions because it is more influenced by solar activity.
    The data comes from ionograms taken at noon in Canberra, Australia..

     
  33. Propagation conditions can be unexpectedly disrupted due to solar storms, which affect the D-Region. This region may block signals in all the HF bands and in particular below 10 MHz.
     
  34. Blackouts:
    1. The radio blockouts associated with solar flares occur during daytime and are most intense when the sun is directly overhead.
    2. In a typical solar flare, X-Ray penetrate to the bottom of the ionosphere (to around 80 Km) and enhance the ionization of the D-region, which absorbs the lower HF bands.
    3. Solar protons can also disrupt HF radio communication. These energetic protons are guided by Earth's magnetic field, such that they collide with the upper atmosphere near the north and south poles. The fast-moving protons have an effect similar to the X-ray flares and create an enhanced D-region thus blocking HF radio communication near polar caps.
    4. During auroral displays, the precipitating electrons can enhance other layers of the ionosphere and have similar disrupting and blocking effects on radio communication. This occurs mainly on the night side of the polar regions of Earth where the aurora is most intense and most frequent.
  35.  
  36. Forecasting HF propagation conditions requires mathematical models using solar solar indices (SSN, SF), geomagnetic indices (K and A), frequency of operation, time of day, and season.
  37.  
  38. Alternatively, you can view the current skywave propagation conditions at a glance.

 

↑ References   Links to external references open in a new tab.

The references below are organized by topic, as follows:
  1. A list of websites with online data and images relayed on this page
  2. Monitor Band Activity of Radio Amateurs Real-time watching of worldwide hams' activity
  3. Waves, EM Radiation, PropagationRadio propagation modes
  4. Skywave Propagation via Ionosphere PropagationIonospheric Intro & ModelLayers/RegionsMUF-OWF-LUFSeasonal & AnomaliesProbing Ionosphere
  5. NVIS unique mode of a skywave
  6. Greyline
  7. Propagation Indices
  8. Observations of The Sun, Space weather, Terrestrial, TEC Total Electron Content, MUF from ionosondes, Propagation Charts
  9. Solar Phenomena
  10. Space Weather Geomagnetic storms & Aurora–Impact on HF radio Propagation | Space Weather Agencies & Services
  11. Forecast Solar Activity, Space Weather Events, and Radio Communication's Disturbances
  12. Tools and Applications for analyzing and forecasting HF propagation
  13. Misc. references; basic concepts; definitions, cross-disciplinary research etc.

  1. Online data and images are relayed on this page from these websites:
    1. ASWFC – Space Weather Service (SWS)↑ | Australian Space Weather Alert System↑
    2. British Geological Survey↑
    3. DLR – German Aerospace Center↑
    4. ESA – The European Space Agency Network↑
    5. NASA Solar Data Analysis Center↑
    6. NOAA Space Weather Prediction Center (SWPC)index↑
    7. Rice Univ. Space Institute↑
    8. The Royal Observatory of Belgium↑
    9. hamqsl.com, Paul L Herrman, N0NBH↑
    10. prop.kc2g.com, Andrew D Rodland, KC2G↑
    11. hb9vqq.ch, Roland Gafner, HB9VQQ↑
    12. hf.dxview.org, Jon Harder, NG0E↑
    13. qrzcq.com, QRZCQ↑
    14. solen.info, Jan Alvestad, retired from FMC Kongsberg Subsea AS, Norway↑
    15. spacew.com, Solar Terrestrial Dispatch↑

  2.  
  3. Monitor HF Band Activity of Radio Amateurs ↑ Real-time watching of worldwide hams' activity

      Software-Defined Radio (SDR) is a technology where analog hardware components are replaced by software.

    1. SDR - Software Designed Radio Wikipedia ↑
    2. Unique SDR receivers

    3. Malakhite DSP portable SDR radio receiver (Russian) Russian hamforum
    4. Malahit DSP1 and DSP2 clone receivers A youtube playlist of demos and explanarions Doron, 4X4XM
    5. BELKA SDR Pocket RX 10 KHz - 31 MHz A youtube playlist of demos and explanarions Doron, 4X4XM
    6. There are two worldwide networks of remote public SDR receivers↑

    7. WebSDR list of public stations
    8.  
    9. KiwiSDR map of public stations

    Activity Charts and DX Clusters

    1. Real-time Ham Band Activity Map Jon Harder, NG0E
    2. Sites for Checking Signal Propagation and Band Activity South Pasadena Amateur Radio Club (W6SPR)
    3. DXMAPS Gabriel Sampol, EA6VQ
      A video demo of DXMaps OfficialSWLchannel,
      This website displays maps and lists of recent QSOs on various ham bands (from LF to UHF) that may indicate real-time propagation conditions.
    4. Real-time propagation and band conditions QRZ online
    5. HamDXMap : MUF, foF2, live radio frequencies weather Christian Furst, F5UII
      Map for amateur radio uses (HamRadio) : In the shape of a terrestrial world globe, the MUF and Aurora Borealis layer. This gives the distances and directions of antennas between amateur radio stations, the position on the Maidenhead Locator grid.
    6. DXWatch custom DX filter Spot Search and Create Your Filter DXWatch—Felipe, PY1NB
    7. DXZone: Amateur Radio Internet Guide; incl. curation of 51 DX clusters nodes. DXZone
    8. Reporters of digital modes

    9. Display Reception Reports PSKReporter
    10. Using PSK Reporter Website as a Propagation Tool eHam.net
    11. HF Signal Propagation Reporter, PSK/JT65/FT-8/CW/JT9 HamRadioConcepts KJ4YZI
    12.  
      APRS-IS - Automatic Packet Reporting System-Internet Service
       
    13. Find Real-time Contacts, DX Cluster, Spotter Network, APRS  HamRadioConcepts KJ4YZI
    14. VHF Propagation Map APRS-IS real-time radio propagation from stations operated near 144 MHz
    15. WSPR - Weak Signal Propagation Reporter ↑

    16. WSPRnet Weak Signal Propagation Reporter website
    17. WSPR Rocks — An alternative map VK7JJ
    18. WSPR Live: Tools for the analysis of WSPR spot data.
    19. Weak Signal Propagation Reporter Wikipedia
    20. WSPR - An Introduction for Beginners | WSJT-X Ham Radio Ham Radio DX, 7-Jan-2022
    21. WSPR Explained: How to Get Started With One-Way Ham Radio ExtremeTech
    22. Average propagation conditions: The recent WSPR reports on 80–10m Ham Bands up to 60 days WSPR Rocks
    23. Beacons

    24. NCDXF Beacon Network see above ↑
    25. International Beacon Project NCDXF
    26. Beacons IARU
    27. International Beacon Project (IBP) Wikipedia
    28. Worldwide List of Beacons (1.8–28 MHz) RSGB
    29. High Frequency Beacons and Propagation VU2AWC
    30. Amateur Radio Propagation Beacon Wikipedia
    31. Ham Radio Beacon List Google
    32. Types of Radio beacon HF Underground
    33. Investigating Radio propagation using beacons HF Underground
    34. Reverse Beacon Network (RBN) | History | Online Activity
    35. Beacon monitoring programs DXZone
    36. Detect Changes in Propagation Conditions by RBN, WSPR, PSKR etc.

    37. Ham Radio Reporting Networks are useful to assess radio propagation conditions. HamSCI
    38. Using the WSPR Mode for Antenna Performance Evaluation and Propagation Assessment on the 160-m Band 2022 Jurgen Vanhamel et al.
    39. Ionospheric Sounding Using Real-time Amateur Radio Reporting Networks (2014) Nathaniel A. Frissell, W2NAF et al.
    40. Reverse Beacon Networks – PSK Reporter And WSPR 2013 Fred Kemmerer, AB1OC
    41. Interpreting WSPR Data for Other Communication Modes 2013 Dr. Carol F. Milazzo, KP4MD
     

  4. Waves, EM Radiation, Propagation

    Electromagnetic (EM)

    1. Electromagnetic radiation Wikipedia
    2. The Electromagnetic spectrum spans from 3 Hz to 3x1018 Hz (wavelength: 108 m–1-10 m) Wikipedia
    3. The radio spectrum spans from 3 Hz to 3x1012 Hz (wavelength: 108 m–1-4 m) Wikipedia
    4. Shortwave radio from 3 to 30 MHz (100 to 10 meters) Wikipedia
    5. Radio Waves Propagation

    6. Introduction to RF Propagation John S. Seybold
    7. Wave Behaviors NASA Science
    8. Critical frequency Wikipedia
    9. Diffraction Wikipedia
    10. High Frequency 3 and 30 megahertz (MHz) Wikipedia
    11. Radio EM Wave Reflection Electronics-Notes
    12. Radio Propagation from Extremely Low Frequency (ELF) to Far infrared (FIR) Wikipedia
    13. Radio Wave Propagation Fundamentals Chapter 2 KIT.edu
    14. Radio Propagation Tutorial Basics Electronics-Notes
    15. Reflection of EM waves Wikipedia
    16. Refraction Wikipedia
    17. Scattering Wikipedia
    18. Ionospheric Radio Propagation A youtube playlist Doron, 4X4XM
    19. Propagation Overviews

    20. The Rebirth of HF Rohde & Schwarz
    21. Course Overview: Atmospheric Effects on Electromagnetic Systems Naval Postgraduate School
    22. All-In-One Overview: There is nothing magic about propagation José Nunes – CT1BOH (2021)
    23. Overview: Understanding HF / VHF / UHF / SHF Propagation (PDF) Paul L Herrman N0NBH
    24. High Frequency Communications – An Introductory Overview - Who, What, and Why? Bill Foose @ HIARC meeting
    25. Propagation of Radio Waves Basu, VU2NSB principles and methods
    26. Propagation Modes↑

    27. Line-of-sight propagation (LOS) Wikipedia
    28. Non line-of-sight propagation Wikipedia
    29. Ground Wave

    30. Ground Wave Propagation Wikipedia
    31. Ground Wave Propagation Tutorial Electronics-Notes
    32. Ground wave MF and HF propagation ASWFC Part of key topics within ionospheric HF propagation
    33. Ground Wave Propagation (Tutorial) BYJU’S Tuition Center
    34. Skip zone Wikipedia
    35. Skywave / Skip

    36. Skywave or Skip Propagation Wikipedia
    37. Skywaves & Skip Zone Electronics-Notes Key topics within ionospheric HF propagation
    38. Path length and hop length for HF sky wave and transmitting angle ASWFC
    39. Complex Propagation modes↑

    40. Complex propagation modes of HF sky wave
    41. Atmospheric Ducting Wikipedia
    42. Tropospheric Ducting Wikipedia
     

  5.  
  6. Skywave Propagation via the ionosphere ↑
            PropagationRefractive IndexIonospheric IntroModelLayers/RegionsMUF-OWF-LUFSeasonal & AnomaliesIonosphere Probing

      Ionospheric / Skywave Propagation

    1. HF Progagation: The Basics - QST, December 1983 Denis J. Lusis, W1JL/DL
    2. The HF Bands for Newcomers (An Overview), ARRL (2007) Gary Wescom, N0GW
    3. An Introduction to HF propagation and the Ionosphere (1999 - 2009) Murray Greenman, ZL1BPU
    4. Introduction to HF Propagation (33 pages presentation, Nov 2018) Rick Fletcher, W7YP
    5. An introduction to HF Propagation (2022) Sean D. Gilbert Mipre, G4UCJ
    6. The Ionosphere June 2024 Andrew McColm, VK3FS
      The ionosphere, generated by solar radiation, plays a crucial role in radio communication with the D, E, and F2 regions outlined in this video.
    7. The Ionosphere Part 2 Aug 2024 Andrew McColm, VK3FS
      Ionized oxygen atoms in the E region are critical to good DX in the 50–144 MHz bands. EUV and activity from our sun affect the MUF and LUF in the 3–30 MHz bands.
    8. Propagation of radio waves explained Jean-Paul Suijs, PA9X
      Radio waves; Earth’s atmosphere (from Troposphere to Ionosphere); Main Propagation modes; Ionospheric layers; Solar Activity; Sunspots and Solar Flux; Solar Wind; Earth’s Geomagnetic Field; Solar Flares; Coronal Holes; CME; The 27-day cycle; The sunspot cycle; The Earth’s seasons; How HF propagation is affected by solar activity: Flares, Coronal holes, CME; Unique propagation effects: Sporadic-E, Backscatter, Aurora, Meteor scatter, Trans-Equatorial, Field Aligned Irregularities.
    9. When is the best time to make an HF contact? Propagation Prediction tools Ria's Ham Shack Ria Jairam, N2RJ, 7 April 2022
      When is the ideal time to make HF contact with a specific region of the world?
      A general talk of about 18 minutes, without demonstrations or definitions of basic concepts.
    10. Ionospheric propagation Basics Electronics-Notes
    11. Introduction to Ionospheric HF Radio Propagation ASWFC
    12. Understanding HF Propagation Rohde Schwarz
    13. Understanding HF Propagation Steve Nicols, G0KYA, RSGB
    14. Radio Propagation 101 - Why should you be interested in propagation? Dan Vanevenhoven
    15. Ward Silver On Radio Wave Propagation Ham Radio Crash Course
    16. The Ionosphere, Shortwave Radio, and Propagation MIT Film & Video Production club
    17. The Effects Of The Ionosphere On Radio Wave Propagation An Excellent Presentation made more than 86 years ago!!! Art Bodger
    18. Ionospheric Propagation University of Toronto
    19. Regional and Long Distance Skywave Communications Ken Larson, KJ6RZ
    20. Transequatorial Radio Propagation CO8TW
    21. Ionospheric Research

    22. Welcome to the Ionosphere NASA Goddard
    23. Ionization (basics) Wikipedia
    24. Plasma (basics) Wikipedia ↑
    25. Plasma recombination Wikipedia ↑
    26. The Ionosphere UCAR
    27. Ten Things to Know About the Ionosphere NASA
    28. Ionosphere Electronics-Notes
    29. Refractive index (Optics) Wikipedia ↑ The refractive index of the ionosphere
    30. Refractive Index of Ionosphere Calculator Calculator A to Z
    31. The refractive index and the absorption index of the ionosphere Research notes
    32. Ionosphere and Radio Communication Saradi Bora, Kamalabaria College, North Lakhimpur, Assam, India
      The ionospheric refractive index P.126
    33. Refractive index of ionosphere Plasma Physics
    34. Ionospheric Radio Wave Propagation Richard Fitzpatrick, University of Texas at Austin
    35. The Complex Refractive Index of the Earth's Atmosphere and Ionosphere Ernest K. Smith, University of Colorado
    36. The Earth's Ionosphere (book 1989) Plasma Physics and Electrodynamics Michael C. Kelley
    37. Ionospheric model

    38. Ionosphere (basics) Wikipedia
    39. Introduction to the ionosphere Anita Aikio. Dept. Physics, University of Oulu, Finland
    40. Ionospheric model Wikipedia
    41. Ionospheric Radio (book 1990) Kenneth Davies
    42. Layers / Regions

    43. Mesopause Wikipedia ↑
    44. Distribution of ionospheric free-electrons Bob Brown, NM7M (SK), Ph.D.
    45. The Ionosphere and the Sun Naval Postgraduate School
    46. Layers of Ionization Wikipedia
    47. Ionospheric D, E, F, F1, F2 Regions Electronics-Notes
    48. D Layer Wikipedia
    49. Ionospheric D Region Britannica
    50. D-region absorption of radio signals Ham Radio School
    51. Day vs Night Ionospheric Layers Northern Vermont University Lyndon Atmospheric Sciences
    52. E-region Wikipedia
    53. Sporadic E propagation Wikipedia
    54. Sporadic E-region ScienceDirect
    55. Sporadic E Propagation in 2 minutes Andrew McColm, VK3FS
    56. Sporadic E Propagation Andrew McColm, VK3FS
    57. Sporadic E propagation (Es) Andrew McColm, VK3FS
    58. Understanding Sporadic E Propagation for VHF DX Ham Radio DX
    59. Understanding Sporadic E Rohde Schwarz
    60. F-region Wikipedia
    61. MUF, OWF, and LUF - Explanation of the concepts; see below How is MUF determined?

    62. HF Radiation - Choosing the Right Frequency Naval Postgraduate School
    63. MUF Maximum usable frequency Wikipedia
    64. Critical frequency, MUF, OWF, and LUF Electronics-Notes
    65. How to use Ionospheric Propagation? Electronics-Notes ↑
    66. Ionospheric variations

    67. Sunspot Number and critical frequencies and Time (Years and Seasons) ASWFC
    68. Season Rollover – Why do shortwave frequencies have to change? Neale Bateman, BBC
    69. The Seasonal Behavior of the Refractive Index of the Ionosphere over the Equatorial Region Turkish Journal of Science & Technology
    70. Ionospheric anomalies

    71. Persistent anomalies to the idealized ionospheric model Wikipedia
    72. Effect of Seasonal Anomaly or Winter on The Refractive Index of in Height of The Ionospheric F2-Peak International Journal of Basic & Applied Sciences
    73. Ionosphere Probing Principles | Ionosondes | Ionograms | Stations | Charts | R & D

    74. Radio Techniues for Probing the Terrestrial Ionosphere (book 1989) R.D. Hunsucker
    75. Introduction To Ionospheric Sounding (2006) Bruce Keevers, National Geophysical Data Center, NOAA
    76. Principles - Theoretical and Methodolical Aspects

    77. Chirping Explained - Passive Ionospheric Sounding and Ranging Peter Martinez, G3PLX
    78. Chirp reception and interpretation (2013) Pieter-Tjerk de Boer, PA3FWM
    79. Software-Defined Radio Ionospheric Chirpsounder For Hf Propagation Analysis (2010) Nagaraju, Melodia (NYSU); Koski (Harris Corporation)
    80. International Reference Ionosphere model IRI
      IRI, an international project, established a Working Group in the late 1960s to create an empirical standard model of the ionosphere. It is sponsored by the Committee on Space Research COSPAR and the International Union of Radio Science URSI
    81. Ionosondes ↑

    82. Introduction to Ionospheric Sounding for Hams Dr. Terry Bullett. W0ASP - University of Colorado
    83. Ionosonde Wikipedia
    84. Ionosonde HF Underground
    85. DIGISONDE®: Simultaneous Ionospheric Observations Around The Globe Lowell Digisonde International (LDI)
    86. Ionograms ↑

    87. Ionogram Wikipedia
    88. Understanding HF Propagation and Reading Ionograms  Bootstrap Workbench
    89. Ionogram Information Hamwaves - Serge Stroobandt, ON4AA
    90. Digisonde Directogram UMass Lowell Space Science Lab website, MA, US
    91. Digital Ionogram DataBase Global Ionosphere Radio Observatory (GIRO)
    92. Mirrion 2 - Real Time Ionosonde Data Mirror Space Weather Service at NOAA
    93. Ionogram Data Info GIRO, UML
    94. The Defence Science and Technology Group High-Fidelity, Multichannel Oblique Incidence Ionosonde (2018) DOI AGU
    95. Remote sensing of the ionosphere Google Search
    96. Probing ionospheric disturbances by Auroral Radar Network ↑

    97. Super Dual Auroral Radar Network (SuperDARN) Wikipedia
    98. First Observations of Large Scale Traveling Ionospheric Disturbances Using Automated Amateur Radio Receiving Networks (2022) Nathaniel A. Frissell, W2NAF et al.
     

  7.  
  8. NVIS a unique mode of a skywave: real-time map↑, explanation↑
     
    1. Understanding NVIS  Rohde Schwarz
    2. HF NVIS  Military HF Radio
    3. NVIS Wikipedia
    4. NVIS Propagation: Near Vertical Incidence Skywave Electronics-Notes
    5. Near-Vertical Incidence Sky-Wave Propagation 36 pages Presentation for radio hams Gerald Schuler, DU1GS / DL3KGS
    6. Near Vertical Incidence Skywave (NVIS) W8BYH, Fayette ARES
    7. Near Vertical incidence Skywave Propagation NVIS Antennas  80, 60, 40m bands KB9VBR Antennas
    8. NVIS Overview  David Casler, KE0OG
    9. Ham Radio NVIS for Regional Communications  Radio Prepper
    10. NVIS - Near Vertical Incidence Skywave What is it? advantages; antennas; links Jim Glover, KX0U (ex WB5UDE)
    11. Near Vertical Incidence Skywave (NVIS) Ham Radio School, W0STU
    12. NVIS propagation Dave Lawrence, VA3ORP (2007)
    13. NVIS explained - part 1, part 2, part 3 NCSCOUT NVIS explained citing the above 3-parts publication AmRRON
    14. NVIS Antennas Dale Hunt, WB6BYU
    15. Extended Research papers

    16. Mastering HF Communication: Decoding Space Weather Data Final practical notes about NVIS. Chris, N6CTA
    17. Radio communication via NVIS propagation: an overview Telecom Sys (2017) DOI, Ben A. Witvliet, Rosa Ma Alsina-Pagès
    18. Analysis of the Ordinary and Extraordinary Ionospheric Modes for NVIS Digital Communications Channels Sensors (Basel)
    19. NVIS HF signal propagation in ionosphere using calculus of variations Geodesy and Geodynamics, Umut Sezen, Feza Arikan, Orhan Arikan

  9.  
  10. Greyline Propagation ↑
     
    1. Grey Line HF Radio Propagation Electronic Notes
    2. Identifying Gray-Line Propagation Openings DXLab
    3. Greyline Propagation G0KYA
    4. Gray-line Propagation Explained Radio Hobbyist
    5. Round the world echoes G3CWI
    6. An introduction to gray-line DXing Rob Kalmeije
    7. Greyline Map DX QSL Net
    8. Greyline Map DXFUN
       

  11.  
  12. Propagation Indices (Indexes) include Solar Indices and Geomagnetic Indices
            They are used as a measure of Global Propagation Conditions↑
     
    1. Propagation "indexes" or "indices"? Microsoft copilot
    2. Circular of Basic Indices for Ionospheric Propagation ITU
    3. Beginner's Guide for Radio Propagation Indexes May 2024 Greg Lane, N4KGL
    4. Beginners Guide to Propagation Forecasting Ed Poccia, KC2LM
    5. Understanding HF propagation reports Amateur Radio views and reviews for Beginners Rich, VE2XIP
    6. Current Ham Radio Propagation Conditions—Ham Radio for Non-Techies (HR4NT)Scott, KI5NPL
    7. Solar Index and Propagation Made Easy - HF Ham Radio The Smokin Ape
    8. Solar-induced Indices: SFI, SN, A, K, Kp Electronics-Notes
    9. Global Indices - Glossary of Terms HamQSL , Paul L Herrman, N0NBH
    10. What exactly are the key Indicies? Andrew McColm, VK3FS
    11. Making sense of Solar Indices Andrew McColm, VK3FS
    12. What are Solar Flux, Ap, and Kp Indices? Andrew McColm, VK3FS
    13. Focus on Solar Indices↑

    14. The history of the 10.7 cm solar flux Government of Canada
    15. The 10.7 cm solar radio flux K. F. Tapping, AGU
    16. Penticton/Ottawa 2,800 MHz Solar Flux NOAA
    17. Focus on Geomagnetic Indices↑

    18. Planetary K-index NOAA / NWS Space Weather Prediction Center
    19. K-index – Definition & Detailed Explanation Sentinel Mission
    20. K-index Wikipedia
    21. Hp30 and Hp60 vs. Kp index GFZ (German Research Center for Geosciences)

  13.  
  14. Observations
                SolarSpace weatherTerrestrial Geomagnetic Indices, TEC Total Electron ContentPropagation Conditions

      Recent radio-ham records related to HF propagation

    1. Recent records of eSSN / eSFI ( 1y / 3m / 1m / 1w / 1d ) Andrew D Rodland, KC2G courtesy of GIRO, NOAA NCEI, WWROF
    2. Live Ionospheric Data Paul L. Herrman, N0NBH presented by Meteorscan.com
    3. Solar Weather Info HFQso.com - Palmetto Tech Network LLC
    4. Sun data and propagation—The last 36 hours—The last 30 days—WSPEnet—DxCluster QRZCQ
    5. Solar Conditions & Ham Radio Propagation (indices) W5MMW
    6. SolarHam—Real-time Space Weather—Latest Solar Imagery and Alerts Kevin, VE3EN
    7. Live Solar Events—Radio Reflection Detection Andy Smith, G7IZU
    8. Solar Observations↑

    9. CME - Corona Mass Ejection, monitored by LASCO
    10. Current Sunspot Regions Space Weather Live Belgium
    11. Solar Data Analysis Center - serves Solar Images, Solar News, Solar Data, and Solar Research NASA
    12. Solar Resource Page Mark A. Downing, WM7D
    13. Extreme ultraviolet Imaging Telescope (EIT) Wikipedia
    14. Yohkoh Soft X-Ray Telescope Wikipedia
    15. Solar Demon Flare Detection running in real time on SDO/AIA Royal Observatory of Belgium
    16. Current Solar Images SDAC NASA/GSFC–Solar Data Analysis Center, NASA
    17. Sun In Time AIA (Atmospheric Imaging Assembly), relays SDO images courtesy of NASA
    18. SDO Mission NASA - The Solar Dynamics Observatory
    19. SDO guide NASA
    20. The Active Sun from SDO: 30.4 nm NASA - The Solar Dynamics Observatory
    21. EVE Overview Solar Phys. - The Solar Dynamics Observatory
      The EVE project (real-time high-resolution EUV measurements) was designed to improve understanding of the evolution of solar flares
      and extend the related mathematical models used to analyze solar flare events.
    22. Solar storms and space weather

    23. Dr. Tamitha Skov - Space Weather Woman; Wikipedia, Youtube channel, facebook, Homesite
      Dr. Tamitha Skov is a space weather physicist that reviews solar storms and anlyzes how they affect spacewetaher. She specializes in forecasting and analyzing space weather processes in the heliosphere and exosphere. Her work extends to both traditional media and social platforms. As a credentialed space weather forecaster, she helps the public understand the effects of space weather.
    24. Monitor Solar Active Regions - search by date Peter Thomas Gallagher, Irland
    25. Recent Space Weather (24 hours)

    26. Current Space Weather Parameters Solar Wind, X-ray flares, Auroral Storm Potential, Current Magnetic Indices Solar Terrestrial Dispatch
    27. R6 Army MARS: Consolidated Solar Weather Real-time Terrestrial indices due to Solar Weather Region 6 Army MARS
    28. ACE Solar Wind in the last 24 hours NOAA

    29. Solar wind Particles near Earth
    30. Proton Flux from 6 hours to 7 days NOAA - GOES, SWPC
    31. Near-Earth solar wind forecasts (EUHFORIA) provided by ESA

    32. Solar wind Magnetospheric Multiscale (MMS): Four Magnetospheric Multiscale (MMS) spacecraft, flying in a tetrahedral formation, detect charged particles and magnetic fields in space, helping scientists understand how solar wind interacts with Earth’s magnetosphere. This mission, involving Rice University, studies magnetic reconnection, acceleration, and turbulence in space.
    33. Magnetospheric Multi Scale (MMS) See real-time dials, see index Rice University
    34. Magnetic reconnection Wikipedia
    35. Magnetospheric Multiscale Mission Wikipedia
    36. Magnetospheric Multiscale (MMS) Mission NASA
    37. Magnetospheric Multiscale (MMS) NASA, Goddard Engineering and Technology Directorate
    38. Recent days RSG; K and A indices

    39. Recent 3 days: X-ray, proton flux, and geomagnetic activity NOAA
    40. Recent 7 days: K and A indices by station NOAA
    41. Space weather prediction center: index of images NOAA
    42. Terrestrial observations

    43. GOES: Geostationary Operational Environmental Satellite Network NASA
    44. GOES: Geostationary Operational Environmental Satellite" Wikipedia
    45. Latest events (recent Solar Watch) GOES Lockheed Martin Solar & Astrophysics Laboratory (LMSAL)

    46. X-Ray flares—Radiation
    47. Solar Flare ALARM ASWFC
    48. Recent GOES X-ray Flux up to 3 days GOES, NOAA SWPC
    49. Recent flare @ 13.1 nm wavelength NOAA SWPC
    50. X-ray flares recent 6 Hours GOES Relayed by New Jersey Institute of Technology
    51. Solar and Heliospheric Observatory - SOHO ESA & NASA
    52. Views of the Sun taken by SOHO and the Yohkoh soft-Xray telescope at various EUV wavelengths
    53. X-Ray Flares last 3 days from SDO, SOHO, GOES. STEREO Relayed by Spaceweather-live, Belgium
    54. Recent month solar observations

    55. Recent Month Sunspot Number SILSO, Royal Observatory of Belgium
    56. Recent Month Daily Sunspot Number MET Malaysia
    57. Recent Month Solar Activity Plot Australian Space Weather Service
    58. Recent month Solar and geomagnetic data Table copied from Institute of Ionosphere, Kazakhstan Solen-Jan Alvestad
    59. Reviews and comparisons of past Solar observations

    60. May 2024 Solar storms Wikipedia
    61. Geomagnetic storms May 2024 Duckduckgo
    62. Solar Terrestrial Activity Reports Solen-Jan Alvestad
    63. What does the sun’s X-ray flux tell us? Earthsky
    64. Archive of remarkable solar activity and space weather events (select month and year) Space Weather Live
    65. RHESSI: The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is a retired project that watched solar flares daily from 2002 to 2023. NASA
    66. Notable "List of solar storms" Wikipedia

    67. Real-time TEC - Total Electron Content (calculated) ↑

    68. Total Electron Content (TEC) Wikipedia
    69. TEC - Recent theories, methods and models
    70. Near-real-time TEC maps ESA - Europen Space Weather Service
    71. TEC at Ionosphere Monitoring and Prediction Center ESA
    72. One-hour Forecast Global TEC Map DLR (ESA)
    73. Station list DLR (ESA)
    74. Archive of TEC DLR (ESA)
    75. North American TEC NOAA
    76. Near real-time global TEC Map ASWFC
    77. Global Ionosphere Map (GIM) SpringerLink
    78. Real-time MUF estimations using ionograms at different locations

    79. Ionosonde station list UML - University of Massachusetts Lowell
    80. GIRO - Instrumentaion GIRO, UML
    81. About GIRO UML, Center for Atmospheric Research
    82. Real-time foF2 - Plots for Today, Yesterday and the past 5 days (more than 100 links to Inonosonde stations)NOAA
    83. Real-time Ionograms

    84. Recent ionograms (Cyprus) University of Twente, Enschede, Netherlands
    85. Animated ionograms Latest 24-Hour GIRO
    86. Ionosonde stations connected to NOAA NGDC, NOAA
    87. Real-time ionogram near your location Hamwaves - Serge Stroobandt, ON4AA
    88. Ionograms Research Development

    89. Small Form Factor Ionosonde Antenna Development Tyler Erjavec, The Ohio State University
    90. Observations of pole-to-pole, stratosphere-to-ionosphere connection MIT Haystack Observatory
    91. Ionospheric Density Irregularities, Turbulence, and Wave Disturbances during the Solar Eclipse over North America 21 August 2017 MIT Haystack Observatory
    92. Modeling Amateur Radio Soundings of the Ionospheric Response to the 2017 Great American Eclipse Nathaniel A. Frissell, W2NAF et al.
    93. Charts of HF propagation conditions

    94. Current foF2 (NVIS) Propagation Map updated every 15 minutes Andrew D Rodland, KC2G
    95. Current MUF 3000 Km Propagation Map updated every 15 minutes Andrew D Rodland, KC2G
    96. Ionospheric Maps - Current foF2 Plots (Global) ASWFC
    97. Hourly Area Predictions (HAP) Charts of selected regions ASWFC
    98. Current foF2 Plots (Asia & Australia) ASWFC
    99. Amateur Radio Usable HF Frequencies & Forecast Remarkable Technologies, Inc.
      Charts of HF propagation conditions refreshed every 20 minutes.
    100. Global HF Propagation Andy Smith, G7IZU

  15.  
  16. Solar Phenomena— tutorial↑

      Solar Physics

    1. Solar Physics (Heliophysics) Youtube playlist
    2. Heliophysics Wikipedia
    3. Heliophysics NASA
    4. Heliophysics and amateur radio: citizen science collaborations . . . Nathaniel A. Frissell, W2NAF et al.
    5. Quiet Sun Radiation

    6. Solar Radiation / Sunlight Wikipedia
    7. Extreme Ultraviolet (EUV) Wikipedia
    8. Active Sun is it chaotic?

    9. Overview of Solar phenomena Wikipedia - Sunspots (Solar Cycle), flux (SF), solar wind, particle events, flares, CME
    10. Links to types of Solar storms Wikipedia
    11. Sunspots↑

    12. Sunspots Wikipedia
    13. Sunspot Number ASWFC
    14. The Lifetime of a Sunspot Group ASWFC
    15. Effective sunspot number: A tool for ionospheric mapping and modelling URSI General Assembly 2008
    16. Solar Cycle↑

    17. Solar Cycle Wikipedia
    18. Solar minimum Wikipedia
    19. Solar maximum Wikipedia
    20. Understanding the Magnetic Sun NASA
    21. Solar Cycle Progression NOAA
    22. Sunspot number series: latest update SILSO, Royal Observatory of Belgium
    23. North-South Asymetry of Monthly Hemispheric Sunspot Numbers SILSO, Royal Observatory of Belgium
    24. Solar Cycle ASWFC
    25. The Solar Dynamo

    26. The Sun as a Dynamo High Altitude Observatory @ NCAR (2001-2008)
    27. The Solar Dynamo: Plasma Flows Tom Bridgman @ NASA, August 19, 2008
    28. The solar dynamo begins near the surface 2024 Geoffrey M. Vasil et al, Nature
    29. Evolution of Solar and Stellar Dynamo Theory Paul Charbonneau & Dmitry Sokoloff @ Space Science Reviews, Springer 2023
    30. An overlooked piece of the solar dynamo puzzle 2019 HZDR
    31. The Solar Dynamo: The Physical Basis of the Solar Cycle and the Sun’s Magnetic Field 2017 Credible Hulk
    32. The Solar Dynamo: Toroidal and Radial Magnetic Fields 2008 NASA
    33. Understanding the solar dynamo Paul Bushby, Joanne Mason @ Astronomy & Geophysics 2004
    34. Solar Storms ↑

        Solar Flares ↑
    35. Solar Raditaion storms NOAA
    36. Solar Strom scale NOAA
    37. Solar Radiation Storm Space Weather Live
    38. Solar Flare Wikipedia
    39. Classification of X-ray Solar Flares or Solar Flare Alphabet Soup Spaceweather.Com
    40. Understanding how solar flares affect radio communications Barrett Communications, Australia
    41.   Solar Particle Events ↑
    42. Solar Particle Event (SPE) Wikipedia
    43. Solar energetic particles (SEP) Wikipedia
    44. Solar Proton Events Affecting the Earth Environment 1976 - present NASA
    45. Next-Generation Solar Proton Monitors for Space Weather Eos
    46. The Difference Between CMEs and Solar Flares NASA
    47. CME ↑

    48. What is Coronal Mass Ejection Wikipedia
    49. Coronal Mass Ejections - CME NOAA
    50. Particle Precipitation

    51. Particle Precipitation ScienceDirect
    52. Particle Precipitation in the Earth and Other Planetary Systems: Sources and Impacts Frontiers
    53. Energetic particle precipitation Laboratory for Atmospheric and Space Physics, Univ. of Colorado
    54. Cosmic rays vs. sunspot numbersCosmic ray intensity is lower when solar activity is high.

    55. Periodic Variations of Cosmic Ray Intensity and Solar Wind Speed to Sunspot Numbers (2020) Hindawi - Collaborative work
    56. Cosmic Rays 2016 NOAA
    57. Cosmic Rays and the Solar Cycle 2005 University of Delaware

  17.  
  18. Space Weather ↑ What is it?
          Geomagnetic storms & Aurora–Impact on HF radio Propagation | Space Weather Agencies & Services
     
      Space Weather Definition and concepts
       
    1. Space Weather Wikipedia
    2. What Is Space Weather? NOAA
    3. What is Space Weather? Definition ASWFC
    4. Definition of Space Weather Instituto Nacional de Pesquisas Espaciais (INPE), Brazil
    5. A Media Primer for the Solar Cycle and Space Weather NESDIS
    6. Mathematical Models of Space Weather NASA
    7. Space Weather Highlights AGU
    8. Space Weather Naval Postgraduate School
    9. Solar-terrestrial science CSA
    10. Solar Wind Wikipedia
    11. The Magnetosphere Wikipedia
    12. Magnetosphere (MS) NASA
    13. Interplanetary magnetic field IMF Wikipedia
    14. The Interplanetary Magnetic Field (IMF) - Sun’s magnetic field, B(t)x,y,z, Earth’s magnetosphere Space Weather Live
    15. Relating 27-Day Averages of Solar, Interplanetary Medium Parameters, and Geomagnetic Activity Proxies in Solar Cycle 24
    16. Do Intrinsic Magnetic Fields Protect Planetary Atmospheres from Stellar Winds?
    17. Investigation of the relationship between geomagnetic activity and solar wind parameters based on a novel neural network (potential learning)
    18. Space Weather Prediction and forcasting

    19. Space weather: What is it and how is it predicted? SpaceCom
    20. How to Improve Space Weather Forecasting (2020) Eos, AGU
    21. How to Assess the Quality of Space Weather Forecasts? (2021) Eos, AGU
    22. Space Weather Impact on radio communication

    23. Space Weather Indices * Comparison tables * ASWFC
    24. How does Space Weather impact HF radio communication? NOAA
    25. Space Weather and Radio Communications ASWFC
    26. Mastering HF Communication: Decoding Space Weather Data August 2023 Chris, N6CTA
      The article explains how radio amateurs can use real-time space weather data to optimize HF communication. In particular it mentions the Hp30 index, MUF , f0F2, and eSFI. These metrics are crucial for selecting the right frequency bands and forecasting propagation conditions. It provides practical insights and essential links to help enthusiasts determine the best conditions for different types of HF operations, including high-band DX, low-band DX, and NVIS operations. Additionally, it includes tips on antenna optimization to enhance HF communication effectiveness.
    27. The Sun and HF radio propagation Electronic Notes
    28. Space Weather and Propagation (A presentation 2019) Martin Buehring, KB4MG
    29. Solar Activity and HF Propagation (A presentation) Paul Harden, NA5N © QRP-ARCI – 2005
    30. Ionospheric Disturbances ↑

    31. Sudden Ionospheric Disturbance (SID) Wikipedia
    32. Sudden Ionospheric Disturbance (SID) Draft: WFD (23 March 2014) William Denig, National Centers for Environmental Information-NOAA
    33. Sudden Ionospheric Disturbances An overview National Centers for Environmental Information-NOAA
    34. Sudden Ionospheric Disturbances (SIDs) -- Polar Cap Absorption (PCA) events ASWFC
    35. Travelling Ionospheric Disturbances (TIDs), ASWFC
    36. Gamma-ray burst Wikipedia
      Gamma-ray bursts are the most intense explosions in the universe, observed in distant galaxies, with longer-lived afterglows and longer wavelengths emitted.
    37. Evidence of an upper ionospheric electric field perturbation correlated with a gamma ray burst (GRB), Mirko Piersanti et al, November 2023
      Analyzing the October 9, 2022, gamma-ray burst (GRB221009A).
    38. See also Cosmic rays

      Geomagnetic storms ↑

    39. Geomagnetic storms Wikipedia
    40. 5 Geomagnetic Storms That Reshaped Society USGS.gov
    41. Strong geomagnetic storm reaches Earth, continues through weekend May 2024 NOAA
    42. Geomagnetic storms NOAA
    43. The Disturbance Storm Time (Dst) Index NOAA
    44. Geomagnetic storm scale NOAA
    45. Geomagnetic storms Maine Emergency Management Agency
    46. A presentation: Solar Activity and HF Propagation Paul Harden, NA5N © QRP-ARCI – 2005 Pages 85-88 focus on the impact of geomagnetic storms on HF propagation
    47. The impact of geomagnetic storms on HF propagation Bing Search
    48. Space weather impact on radio wave propagation Feb 2023 Norbert Jakowski, German Aerospace Center (DLR), Institute for Solar-Terrestrial Physics
    49. Monitoring and forecasting of ionospheric space weather - effects of geomagnetic storms 2002 J. Lastovicka, Institute of Atmospheric Physics, Czech Republic
    50. Effect of magnetic storms (substorms) on HF propagation: A review D. V. Blagoveshchenskii, Geomagnetism and Aeronomy volume 53, pages 409–423 (July 2013)
    51. High-Frequency Communications Response to Solar Activity in September 2017 as Observed by Amateur Radio Networks AGU
    52. Effect of Weak Magnetic Storms on the Propagation of HF Radio Waves Kurkin, V. I. ; Polekh, N. M. ; Zolotukhina, N. A. (Feb 2022)
    53. HF Propagation during geomagnetic storms at a low latitude station Physics & Astronomy International Journal 2020
    54. Enhanced Trans-Equatorial Propagation following Geomagnetic storms Oliver P. Ferrell, Nature volume 167, pages 811–812 (1951)
    55. Aurora

    56. Aurora Wikipedia
    57. Aurora NOAA SWPC
    58. The Science, Beauty, and Mystery of Auroras NOAA SWPC
    59. The Auroral E-region is a Source for Ionospheric Scintillation EOS
    60. The auroral E-region ionization and the auroral luminosity Omholt, A. (1955)
    61. Auroral Effects on the Ionospheric E-Layer Omholt, A. (1965)
    62. Diffuse Auroral Electron and Ion Precipitation Effects on RCM-E Comparisons With Satellite Data During the 17 March 2013 Storm JGR Space Physics 2019 - Chen, Lemon, Hecht, Sazykin, Wolf, Boyd, Valek
    63. Impacts of Auroral Precipitation on HF Propagation: A Hypothetical Over-the-Horizon Radar Case Study Joshua J. Ruck, David R. Themens
    64. Auroral Propagation RSGB
    65. Radio Auroras Ham Radio Engineering: GM8JBJ
    66. Aurora Event Propagation Gregory A Sarratt, W4DGH
    67. Using Auroral Propagation for Ham Radio Electronics notes
    68. Auroras & Radio Propagation including Auroral Backscatter Electronics notes
    69. Aurora Prediction North Pole NOAA
    70. Aurora Prediction South Pole NOAA
    71. Tonights Static Viewline Forecast Aurora Prediction North Pole NOAA
    72. Tomorrow Static Viewline Forecast Aurora Prediction North Pole NOAA
    73. 3 Day Geomagnetic and Aurora Forecast Kevin, VE3EN
    74. At what Kp index can I see aurora? Doron, 4X4XM
    75. Space Weather agencies and their services

    76. The International Space Environment Service ISES
    77. National Oceanic and Atmospheric Administration NOAA
    78. NOAA Space Weather Prediction Center (SWPC) services:
    79. About NOAA Space Weather Prediction Center Wikipedia
    80. A list of international space weather providers NOAA
    81. Canadian Space Agency CSA
    82. Space Weather Canada SWC
    83. The Embrace Program Instituto Nacional de Pesquisas Espaciais (INPE), Brazil
    84. European Space Agency - Space Weather Service ESA
    85. Space Weather - Met Office UK
    86. Solar Influence Data Analysis Center Royal Observatory of Belgium
    87. Australian Space Weather Forecasting Centre (ASWFC) - Space Weather Services
    88. Overview of the Australian Space Weather Alert System 2022 ASWFC
    89. Australian Bureau of Meteorology, Space Weather Services ASWFC
    90. Korean Space Weather Center RRA/KSWC
    91. Taiwan Space Weather Operational Office Central Weather Administration (CWA)
    92. South African National Space Agency (SANSA) SANSA
    93. Mission Space LEO
    94. Space Weather Canada
    95. World Meteorological Organiztion WMO
    96. American Commercial Space Weather Association ACSWA
    97. Space Weather Forecast National Institute of Information and Communications Technology, Japan NICT, ISES, RWC
    98. China-Russia Consortium Global Space Weather Center

  19.  
  20. Forecast Solar Activity, Space Weather Events, and Radio Communication's Disturbances

      Forecast Solar Activity

    1. Predicted long term sunspot number and Radio Flux at 10.7 cm NOAA / NWS Space Weather Prediction Center ↑
    2. 27-Day Outlook of 10.7 cm Sun Radio Flux and the Earth Geomagnetic Indices NOAA ↑
    3. Solar flares (radio blackouts) NOAA SWPC
    4. Solar Flare Probabilities Kevin, VE3EN
    5. Solar Synoptic Map
    6. Sun news activity, Solar flare, CME, Aurora EarthSky
    7. Space Weather Forecast

    8. Space weather forecast NOAA
    9. RSG forecast ASWFC
    10. Space Weather Forecast Discussion SWPC NOAA
    11. Radio Communications Dashboard SWPC NOAA ↑
    12. * See: Forcasting Aurora events

      Blackout↑ and SID↑

    13. Communications blackout Wikipedia
    14. Radio blackout scale NOAA
    15. D-Region Absorption Prediction (D-RAP) SWPC NOAA
    16. A dynamic collection of propagation information gathered from many different sources Doug Brandon, N6RT
    17. Propagation Links eHam.net Team

  21.  
  22. Tools and Applications for analysing and forecasting HF propagation

    Apps Categories: Real-time Activity / Band Monitoring, real-time maps & Charts, Prediction Software, Mathematical models, etc.

      Mitigation Techniques

    1. Space weather effects on communications systems June 2020 Mark MacAleste, CISA–Cybersecurity and Infrastructure Security Agency
      Effects, Operational Impacts, Mitigations, and Research Gaps for Communications Systems
    2. Online Activity and Band Monitoring

      Gathering information of real-time activity on the ham bands
    3. Real-time Ham Band Activity Map Jon Harder, NG0E
    4. Analyzing Propagation From Active DX Stations Band Activity by (1) Time of Day, (2) Continent DXLab
    5. Radio Propagation Maps Based on established contacts; Choose a propagation map from the menu Andy Smith, G7IZU
    6. Online tools, charts and raw data

      Real-time HF Propagation Tools

    7. HF-START - HF Simulator Targeting of All-users, Regional Telecommunications NICT, Japan
      HF-START - High Frequency Simulator Targeting for All-users’ Regional Telecommunications - is HF propagation simulator that is developed to meet the needs of space weather users for, but not limit to telecommunications: real-time info, web tools, about
    8. HF Propagation Tools Hamwaves - Serge Stroobandt, ON4AA
      Real-time online dashboard of solar activity influencing HF propagation on Earth.
    9. Real‑time HF propagation space weather Hamwaves - Serge Stroobandt, ON4AA
      Real-time online dashboard of solar activity influencing HF propagation on Earth.
    10. Propagation Banners

    11. Add Solar-Terrestrial Data to your Website HamQSL , Paul L Herrman, N0NBH
    12. Real-time Maps & Charts

    13. MUF 3000 Km Map based on Real-time measurements Andrew D Rodland, KC2G ↑
      * Read more about the MUF (3000 km) project
      * Read a review titled: "Developing an Open-Source HF Propagation Prediction Tool".
      Roland Gafner, HB9VQQ, provides an animated map view of the last 24 hours in 15-minute steps.
    14. HamDXMap for the DXer, radio propagation concepts Christian Furst, F5UII
    15. Prediction Software

    16. An Open-Source IRI-based Nowcasting Tool for Ionospheric Electron Density and HF Propagation Andrew D Rodland (2022 Harvard Abstracts)
      An overview of the software and the models behind prop.kc2g.com, a website using the IRI-2016 model, conditioned on near-real-time ionosonde data, to provide global maps of MUF(3000) and foF2. While primarily designed for radio amateur use, this system is useful for nowcasting of F region ionospheric density and mesoscale low elevation HF propagation characteristics.
    17. The Advanced Stand Alone Prediction System (ASAPS) ASWFC
      Australian Space Weather Forecasting Centre offer three software products to predict HF propagation:
      1. GWPS - designed for HF operators working in defence and emergency services
      2. ASAPS Kernel - The Advanced Stand Alone Prediction System designed for government, defence and emergency services
      3. Consultancies - designed for industry, defence and emergency services
    18. S/N HF Propagation Forecast Calculator for the current month DL0NOT
    19. DR2W - Predict Propagation Conditions DK9IP (Winfried), DH3WO (Wolfgang), DJ2BQ (Ewald), ZS1AO/DJ2HD (Mathew)
      A Long-term forecasting cannot take into account unpredicted ionospheric and magnetic disturbances or anomalies
    20. VOACAP Online Application for Ham Radio Jari Perkiömäki, OH6BG / OG6G
      VOACAP forecats monthly average of the expected reliability with diurnal and seasonal variations.
      A Long-term forecasting cannot take into account unpredicted ionospheric and magnetic disturbances or anomalies.
    21. VOACAP Quick Guide Jari Perkiömäki, OH6BG / OG6G
    22. VOACAP Shortwave Prediction Software Rob Wagner VK3BVW
    23. How to use VOACAP - Part 1: Overview, Part 2, Part 3 Jari OH6BG & OH7BG Raisa
    24. VOACAP Charts for RadCom VOACAP
    25. Proppy Online - HF Propagation Prediction James Watson, M0DNS
    26. RadCom online Propagation Prediction Tools RSGB
    27. Ionospheric Characterisation Analysis and Prediction tool (IOCAP) SANSA
    28. IOCAP Application Introduction Video SANSA
      The South African National Space Agency (SANSA) created i/o cap Primary Work Surface, an operational HF communication solution.
      It's a modern, user-friendly HF frequency prediction tool that's simple to use and accurate. In a software program, it blends space weather research and practical HF experience.
    29. DX Toolbox - Shortwave / Ham Radio / HF Radio Propagation Black Cat Systems
      This is a software application that provides a range of tools for HF radio operators, including propagation forecast based on the Solar Terrestrial Dispatch (STL) model.
      It also includes a real-time solar data display and a grayline map.
    30. HF Propagation (Google Play) Android Package Kit
    31. HF Propagation (Microsoft Apps) Stefan Heesch, HB9TWS
    32. Proplab-Pro v3: Review eHam Manual spacew.com
      Proplab-Pro 3.2 (Build 45, March 2023) Three-dimensional ray-tracing ionosphere; can run as standalone; not free.
    33. PROPHF v1.8, HF Propagation predictions Christian, F6GQK
    34. W6ELProp (2002) Sheldon C. Shallon, W6EL
      Predicts skywave propagation between any two locations on the earth on frequencies between 3 and 30 MHz
    35. HamCAP (VOACAP interface) by Alex Shovkoplyas, VE3NEA. Rated 8.93 by DxZone
    36. The Propagation Software Pages A collection of links AC6V
    37. Overviews and reviews of propagation prediction software

    38. What can we expect from a HF propagation model? Luxorion
      Mathematical models and numerical procedures simulate dynamic processes in HF radio propagation, considering interactions between the Sun's and Earth's surfaces, sun, space weather, ionosphere, and atmosphere.
    39. Evaluation of various models for HF propagation prediction SANSA Space Science
    40. Review of HF Propagation analysis & prediction programs Research Oriented Luxorion
      Amateur propagation programs, accessible via the internet, provide graphical solutions and simulate ionospheric effects using near-real-time data or well-known functions, achieving high accuracy.
    41. Review of Propagation prediction programs - VOACAP-based Luxorion
      VOACAP, a US government-funded HF propagation prediction engine, has been continuously improved over the years, with its software technology firmly rooted in the 1980s.
    42. Predicting and Monitoring Propagation DXLab
      * Solar terminator display and prediction - shows greyline at any specified date and time
      * Propagation prediction - provides a graphical view of openings by frequency and time using your choice of the included
      VOACAP, ICEPAC, and IONCAP forecasting engines.
    43.  
    44. PropView DXLab
      PropView forecasts LUF and MUF between two locations over a 24-hour period using VOACAP, ICEPAC, and IONCAP engines. It can specify locations via latitude/longitude entry or DXCC prefix entry. PropView can build schedules for the IARU/HF beacon network and monitor the NCDXF/IARU International Beacon Network. It interoperates with Commander and DXView for automatic monitoring and location display.
    45. RF prop, Radio Propagation & Diffraction Calculator, W6ELProp, PropView, HamCAP DxZone
    46. Radio Propagation Forecasting (2019) Basu, VU2NSB Beacons, VOACAP, CCIR and URSI Models
    47.  

      Ionospheric mathematical models / numerical procedures

    48. ITU-R Directory ITU
      Software, Data and Validation examples for ionospheric and tropospheric radio wave propagation and radio noise
    49. ITU-R P.533 model
      This is an ITU table links to Software, Data and Validation examples for ionospheric and tropospheric radio wave propagation and radio noise in a wide range of propagation conditions. The ITUR HF Prop experimental software, was written by G4FKH and HZ1JB, and is based on the ITU-R P.533 method.
      It uses a probabilistic approach to estimate radio coverage with algorithms that are supposed to be more accurate than other similar programs.
    50. Mathematical Models of Space Weather NASA
    51. Space Weather Modeling Framework (SWMF)
    52. Global Assimilation of Ionospheric Measurements (GAIM) model
    53. Advanced D-region Ionosphere Prediction System (ADIPS)
    54. Ray-tracing models

    55. VOACAP–Voice of America Coverage Analysis Program is a professional hf system performance prediction tool
      VOACAP predicts monthly average expected reliability, considering diurnal and seasonal variations, but does not account for unpredicted ionospheric and magnetic disturbances or anomalies.
    56. General information on the ICEPAC propagation prediction model Jari Perkiömäki, OH6BG
    57. ITUR HF Prop
      Prediction of HF circuits based on Recommendation ITU-R P.533 model - an improved (2017) point-to-point propagation prediction tool, based on an ITU engine, developed by Gwyn Williams, G4FKH.
    58. HFTA - High Frequency Terrain Assessment

    59. Introduction to HFTA - High Frequency Terrain Assessment Nashua Area Radio Society, N1FD
    60. Operating Instructions for HFTA, Version 1.04 (2013) ARRL
    61. HF Terrain Analysis Using HFTA (2015) Stan Gibbs, K0RV
    62. HFTA and Take Off Angles ~ 01/20/2021 RATPAC Amateur Radio
    63. Maximizing Performance of HF Antennas with Irregular Terrain Jim Breakall, WA3FET
    64. Introduction to HFTA – high frequency terrain assessment and more | Request an Azimuthal Map Tom, NS6T
    65. Ionospheric models that simulate a neural network

    66. Neural Network Ionospheric Model (NNIM)
    67. Hybrid ionospheric methods

    68. Application of Machine Learning Techniques to HF Propagation Prediction Richard Buckley, William N. Furman - Rochester, NY

  23.  
  24. Misc. References

      The AI applications used to improve the wording on this website:

    1. Initial chats with ChatGPT 3.5, April 2023
    2. ChatGTP 4o
    3. Copilot Microsoft
    4. Quillbot
    5. Our hobby

    6. Amateur Radio Wikipedia
      The name of the hobby "Amateur Radio" or "Ham Radio" refers to a non-commercial communication, wireless experimentation, self-training, private recreation,
      radiosport, contesting, and emergency communications activity that may use radio transmitters and receivers.
    7. Amateur radio station Wikipedia
      Read about different types of stations used by amateur radio operators.
    8. Radio Amateur Wikipedia
      "Radio Amateur" or "Radio Ham" is the person usualy a licensed operator who communicates with other radio amateurs on amateur radio frequencies.
    9. Number of radio amateurs by country from 2000 to 2022 Ham Radio DX, VK7HH, Hayden P Honeywood
      The IARU officially reported worldwide figures for hams in 2000. The statistics for 2022 are an estimate based on a prior pattern of growth.
    10. Shortwave listening (SWL) Wikipedia
    11. The HF Bands assigned for Radio Amateurs

    12. Amateur Radio Band Characteristics Ham Universe
    13. Ham Radio Bands DXZone
    14. WARC bands Wikipedia
    15. Special articles by Bob Brown, NM7M (SK), Ph.D. U.C.Berkeley

    16. The Little Pistol's Guide to HF Propagation (1996) Bob Brown
    17. HF Propagation Tutorial Bob Brown (SK), NM7M
    18. Communication Modes and Techniques

      FT8

    19. FT8 Wikipedia
    20. FT8 Frequency Chart: Navigating the Digital Mode Landscape Thehamshack, Jerry L Withers, KD7OKK
    21. Digital Voice (DV)

    22. Digital Voice the Easy Way 2023 QST
    23. FreeDV: Open Source Amateur Digital Voice 2023FreeDV
    24. A Guide to Digital Voice on Amateur Radio April 2021 Andrew McColm, VK3FS
    25. How to Use FreeDV Digital Voice Over HF Ham Radio Dec 2020Ham Radio Crash Course
    26. Using FreeDV To Talk On Digital HF 80M Oct 2019 Tech Minds
    27. RSGB 2018 Convention lecture: FreeDV - Digital Voice for HF and other low SNR channels Sept 2019 RSGB
    28. Digital Voice on HF 2013 G4ILO
    29. Will digital voice (on HF) ever be a thing? 2018Dan, KB6NU
    30. International Digital Audio Broadcasting Standards: Voice Coding and Amateur Radio Applications 2003 QEX
    31. Practical HF Digital Voice June 2000 G4GUO, G4JNT , QEX
    32. Automatic link establishment (ALE)

      Automatic Link Establishment (ALE) is a feature that enables a radio station to select the best frequency to establish a connection with another HF radio station or network of stations. It replaces traditional prediction techniques and reliance on trained operators.

    33. Automatic link establishment (ALE) Wikipedia
    34. Youtube clips about ALE:
    35. Free and paid software for ALE:
    36. Automatic Link Establishment Overview 2018 COMMS Working Group
    37. HF Automatic Link Establishment (ALE) 2009 Kingston Amateur Radio Club
    38. ALE HF Network Ham Radio Amateur Radio 2007 Bonnie Crystal, KQ6XA, HFLINK
    39. ALE - The coming of Automatic Link Establishment, QST 1995 Ronald E. Menold, AD4TB
    40. Spread Spectrum

    41. Spread Spectrum Wikipedia
    42. Frequency-hopping spread spectrum Wikipedia

    43. Technological concepts

    44. Satellite Wikipedia
    45. Lagrange points (Google Search) ↑
    46. The Lagrange Mission Wikipedia ↑
    47. Physical concepts

    48. Definition of Physics Wikipedia
    49. Physical Coupling Wikipedia
    50. Collision frequency Wikipedia
    51. Collision frequency Physical Chemistry
    52. Astromonomical concepts

    53. The Solar System Wikipedia
    54. Geometrical concepts

    55. Ecplictic Plane | Plane of the Solar System Wikipedia
    56. Geometrical Optics Wikipedia ↑
    57. Secant Trigonometry term Wikipedia ↑
    58. Geophysical concepts

    59. The atmosphere of Earth Wikipedia
    60. Definition of Aeronomy UMich
    61. Earth's magnetic field Wikipedia ↑
    62. Geonagnetism what is it? Measuring instruments

    63. Origin of Earth’s Magnetic Field Earth.com
    64. Sustaining Earth’s magnetic dynamo Nature
    65. Understand Earth's geomagnetic field through the dynamo effect principle (video) Britanica
    66. Magnetometer Wikipedia
    67. Magnetometers A Comprehensive Guide
    68. Magnetometry D. Waller & B. E. Strauss
    69. Deterministic Chaos ↑

    70. Deterministic Chaos The Exploratorium, 1996
    71. Deterministic Chaos Principia Cybernetica 2000
    72. Concepts: Chaos New England Complex Systems Institute

    73. HF Propagation Research 1958-1990

    74. Basic Radio Propagation Predictions for September 1958, Three Months in Advance National Bureau Of Standards
    75. Ionospheric Radio Propagation 1965 (replaced an obsolete pubication of 1948) Kenneth Davies, National Bureau Of Standards
    76. Solar-Terrestrial Prediction Proceedings | Solar-Terrestrial Prediction Proceedings 1979 Richard F. Donnelly, Space Environment Lab, NOAA
    77. Ionospheric Radio (book 1990) Kenneth Davies
    78. HF Propagation - Novel Research and Analysis

    79. Short and long term prediction of ionospheric HF radio propagation J. Mielich und J. Bremer (2010)
      A modified ionospheric activity index AI has been developed on the basis of ionospheric foF2 observations.
      Such index can be helpful for an interested user to get information about the current state of the ionosphere. Using ionosonde data.
    80. Spread-F occurrences and relationships with foF2 and h′F at low and mid-latitudes in China (2018) Wang, Guo, Zhao, Ding & Lin (Chaina)
       appear as scattered echoes in high-frequency (HF) band ionograms that are known as spread-F events that include frequency spread-F (FSF), range spread-F (RSF), and mixed spread-F (MSF) events.
    81. Long-Term Changes in Ionospheric Climate in Terms of foF2 Jan Lastovicka (2022)
      There is not only space weather; there is also space climate. Space climate includes the ionospheric climate, which is affected by long-term trends in the ionosphere.
    82. Ionospheric Monitoring and Modeling Applicable to Coastal and Marine Environments Ljiljana R. Cander and Bruno Zolesi (2019)
    83. Statistically analyzing the ionospheric irregularity effect on radio occultation M. Li and X. Yue, Atmos. Meas. Tech., 14, 3003–3013, 2021
    84. Analysis of Ionospheric Disturbance Response to the Heavy Rain Event Jian Kong, Lulu Shan, Xiao Yan, Youkun Wang - Remote Sens. 2022, 14(3), 510
    85. A simplified HF radio channel forecasting model Advances in Space Research, Volume 69, Issue 6, 15 March 2022, Pages 2477-2488, Moskaleva, Zaalov
      Estimating the maximum electron density in the ionosphere in relation to the critical frequency of the ionospheric F2 layer (foF2). The suggested forecasting model estimates the electron density profile one day ahead. Comparisons of observed and predicted vertical ionograms indicate the technique's utility.
    86. Ionospheric current Upper Atmospheric Science Division of the British Antarctic Survey
    87. Radio Propagation Prediction for HF Communications (2018) Dept. of Appl/ Physics & Tel., Midlands State Univ., Gweru, Zimbabwe
    88. A Preliminary Systematic Study of HF Radio Propagation from a Source in the Subarctic
      Using HAARP and the Ham WSPR Network (2018)
      Citizen Space Science, Fallen, C. T.
    89. The influence of high latitude off-great circle propagation effects on HF communication systems and radiolocation M. Warrington, A.J. Stocker, N. Zaalov (2002)
    90. Analyzing the current ionospheric conditions Google search
    91. Recent Theories, Methods and Models

    92. Develop ionosphere computer models to enhance HF radio propagation Military Aerospace 2022
      Develop new ways to model the ionosphere in real time to help predict the propagation of high-frequency (HF) radio waves for improved communications and sensing.
    93. Recommendation: Ionospheric Characteristics And Methods Of Basic MUF, Operational MUF AND Ray-Path Prediction ITU 1995
    94. Recommendation: Propagation Factors Affecting Frequency Sharing In HF Terrestrial Systems ITU 1994
    95. Recommendation: HF propagation prediction method ITU 2001
    96. Comparison of observed and predicted MUF(3000)F2 in the polar cap region Radio Science AGU (2015)
      Comparison of ICEPAC, VOACAP, and REC533 models reveal diurnal and seasonal variations. Summer diurnal variation is not represented by the VOACAP or ICEPAC models. REC533 surpasses VOACAP during the winter and equinox months. ICEPAC performs poorly during periods of low solar activity.
    97. Investigation of Two Prediction Models of Maximum Usable Frequency for HF Communication
      Based on Oblique- and Vertical-Incidence Sounding Data (2022)
      atmosphere MDPI
      MOF were compared to predicted MUF. The INGV model outperformed for MUF prediction over Beijing
      and its adjacent mid-latitude regions, according to the root-mean-square error comparison.
    98. Investigation of Two Prediction Models of Maximum Usable Frequency for HF Communication
      Based on Oblique- and Vertical-Incidence Sounding Data (2022)
      atmosphere MDPI
      MOF were compared to predicted MUF. The INGV model outperformed for MUF prediction over Beijing
      and its adjacent mid-latitude regions, according to the root-mean-square error comparison.
    99. ITM Processes

    100. Terrestrial Atmosphere ITM (Ionosphere, Thermosphere, Mesosphere) Processes NASA Visualization (2018)
    101. Detection of Rapidly Moving Ionospheric Clouds H. Wells, J. M. Watts, D. George (1946)
    102. Three-dimensional simulation study of ionospheric plasma clouds S. Zalesak, J. Drake, J. Huba (1990)
    103. Nonlinear Three-Dimensional Simulations of the Gradient Drift and Secondary Kelvin–Helmholtz Instabilities in Ionospheric Plasma Clouds Almarhabi, Lujain & Skolar, Chirag & Scales, Wayne & Srinivasan, Bhuvana (2023)
    104. Articles about "Ionospheric Plasma Bubbles" Google search
    105. Articles about "Ionospheric Plasma Clouds" Google search
    106. Vertical Coupling (Troposphere - Ionosphere)

    107. Sprite (lightning) Wikipedia
    108. ICON - Ionospheric Connection Explorer Wikipedia
    109. Upper-atmospheric lightning Wikipedia
    110. Transient Luminous Events: Lightning above our atmosphere AccuWeather
    111. NASA ScienceCasts: Observing Lightning from the International Space Station NASA
    112. Severe Weather 101: Lightning Types NOAA
    113. Transient Luminous Events (TLEs) SKYbrary
    114. Investigations of the Transient Luminous Events with the small satellites, balloons and ground-based instruments Safura Mirzayeva 2022 Master Thesis
    115. Stunning jellyfish sprite seen in the night sky during Texas storm Aug 2020 The Weather Network
    116. Solar cycle changes to planetary wave propagation and their influence on the middle atmosphere circulation (1997) Arnold & Robinson, Annales Geophysicae, vol. 16, no. 1, pp. 69–76, 1998
    117. Electrodynamical Coupling of Earth's Atmosphere and Ionosphere: An Overview (2011) International Journal of Geophysics
    118. A review of vertical coupling in the Atmosphere-Ionosphere system:
      Effects of waves, sudden stratospheric warmings, space weather, and of solar activity
      (2015) Journal of Atmospheric and Solar-Terrestrial Physics
    119. Electrodynamical Coupling of Earth's Atmosphere and Ionosphere: An Overview (2020) University of Lucknowת India
    120. A Review of Low Frequency Electromagnetic Wave Phenomena Related to Tropospheric-Ionospheric Coupling Mechanisms (2012) NASA
    121. Influence of lightning on electron density variation in the ionosphere (2015) University of Cape Town, Dsc Thesis
    122. TEC variations detected over southern Africa due to lightning storms published by South African National Space Agency
    123. Statistical Study of Global Lightning Activity and Thunderstorm-Induced Gravity Waves in the Ionosphere (2023) Swati Chowdhury, New Zeeland
    124. Eyes on the Earth Earth's Weather / Tropospheric Weather NASA/JPL
 

↑ Index of Terms

  1. A glossary of basic terms
  2. A list of terms that are explained on this website.
  3. Search terms addressed on this website.

 

↑    Last but not least:

The world is changing as the radio amateur spectrum is being sold off to commercial users since few amateurs operate SHF and above.

We did, however, gain new narrow bands in the short, medium, and long wave bands. It may not be enough, but it opens up new avenues for communication improvement that do not rely on commercial infrastructure.

If you have comments, questions or requests please e-mail.

73 de Doron, 4X4XM

 
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