What are ionospheric clouds?

This page is part of the project "Understanding HF Propagation"
by Doron Tal, 4X4XM

The ionosphere is a part of Earth’s upper atmosphere that is ionized by solar radiation, meaning it contains a high concentration of free electrons and ions, concentrated in regions, as illustrated below:

A model of the ionospheric regions

All these ionospheric regions consist of different concentrations of free electrons, i.e., "clouds" or "bubbles", as illustrated below:

The moving plasma clouds are travelling 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.

Read a Summary of the theoretical topics of HF radio propagation. See also an index of terms for HF Radio Propagarion.

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