↑ Radio Communication and the Ionosphere
The role of D, E, and F regions

By Doron Tal, 4X4XM

The ionosphere is a region in the upper-atmosphere that meets space (exosphere).

A mixture of free electrons and ions (known as "plasma") is created when solar radiation ionizes gases 48 to 600 km above the surface of the earth.

The high densities of free electrons significantly affect radio communication.

The ionosphere can be divided into regions, D, E and F:

  1. D Region
    2. The D-region refers to the lowest "layer". It is observed at altitudes ranging from 60 to 90 kilometers.
    The largest part of the HF absorption takes place in the D-region, in particular frequencies lower than 10 MHz.
    The typical (noon time) free electron density ~1010 electrons/m3 at  60-90 km, consists NO+ Nitric Oxide ionized by 1216Å UVC
  2. E Region
    3. E region is above the D region, between 100 to 250 km. The air density is lower compared to the D region. This region affects radio waves differently compared to other regions. The typical (noon time) free electron density ~1011 electrons/m3 at  100-150 km, consists O2+ Oxygen ionized by 10-100Å EUV
  3. F Region
    4. The F region is regarded as the most important ionosphere region for radio communication. This region is divided into F1 (lower) and F2 (higher). The typical (noon time) free electron density ~1012 electrons/m3 at 200-300 km, consists H+, He+ Hydrogen and Helium ionized by 100-1000Å EUV

What are the differences among ionospheric region D, E, and F? a summary
The ionosphere is divided into layers (or regions), D, E, and F from about 48 up to more than 600 Km above the earth`s surface, characterized by different free electron densities, and ion compositions.
D-E-F region Day/Night
Illustration of Ionospheric regions (layers)

During the day the F-region splits into two region called F1 and F2, while the D-region vanishes completely at night. These regions do not have sharp boundaries, and the altitudes at which they occur vary during the course of a day and from season to season.

What makes the ionospheric layers distinct?   See graph of plasma density vs altitude.


Typical Ionospheric electron density profiles

  1. E-region ~1012 electrons/m3 at 150-600 km, consists H+, He+ Hydrogen and Helium ionized by 100-1000Å EUV
  2. E-region ~1011 electrons/m3 at  90-150 km, consists O2+ Oxygen ionized by 10-100Å EUV
  3. D-layer ~1010 electrons/m3 at  50-90 km, consists NO+ Nitric Oxide ionized by 1216Å UVC
    4. Moreover, X-ray Solar Flares, 1-10 Å (hard X-ray), enhance D-layer, causing Blackout events.

As the ionosphere changes, numerous natural and man made systems are affected:

  1. The density of free electrons in the ionophere has an effect on radio waves. Thus it plays an important role in modern communication and navigation systems. As a result, we can obtain signals from radio and GPS systems. In both cases, the composition and density of the ionosphere can significantly affect the signals.

  2. The ionosphere can be influenced by the weather. Different weathers like thunderstorm systems, hurricanes can create pressure waves that ripple up into the Ionosphere. NASA has done research on this matter and within the past 15 years, NASA satellites revealed the connections between the weather condition changes in Earth’s Ionosphere. The ionosphere is impacted also by space weather.

  3. The ionosphere is home to several spacecraft, including the international space station. This suggests that these satellites may be affected by the ionosphere's constantly shifting properties. This also covers the sudden surges of charged particles, which can shorten satellites' orbital lifetimes and increase drag.

Read more about the impact of the ionosphere on radio communication. See also an index of terms for HF Radio Propagarion.

The project "Understanding HF Propagation" provides a detailed overview and tutorials on HF propagation.
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