Solar Flares and Disturbances for Radio Propagation
An overview of the basics of solar flares and other disturbances including CMEs and how they affect ionospheric HF radio propagation conditions for two way radio communications, maritime mobile radio communications, point to point radio communications and radio broadcasting.
As electromagnetic waves, and in this case, radio signals travel, they interact with objects and the media in which they travel. As they do this the radio signals can be reflected, refracted or diffracted. These interactions cause the radio signals to change direction, and to reach areas which would not be possible if the radio signals travelled in a direct line.
The condition of the Sun has a major impact on ionospheric radio propagation. Accordingly it affects a variety of forms of HF radio communications including two way radio communications, maritime mobile radio communications, general mobile radio communications using the HF bands, point to point radio communications, radio broadcasting and amateur radio communications.
As the Sun provides the radiation that governs the state of the ionosphere and hence HF radio propagation, any flares or other disturbances are of great importance. Under some circumstances these can enhance radio communications and the HF radio propagation conditions. Under other circumstances they can disrupt radio communications on the HF bands, while at the same time providing some radio propagation conditions that can be used at VHF by radio amateurs.
there are a number of types of disturbance that are of particular interest for radio communications. Flares are one of the most obvious. However, apart from solar flares there are other disturbances that occur. One is the coronal mass ejection, and there are also coronal holes.
Solar flares are enormous explosions that occur on the surface of the Sun. They result in the emission of colossal mounts of energy. In addition to this, the larger solar flares also eject large amounts of material mainly in the form of protons.
Flares erupt in just a few minutes with apparently no warning. When they occur the material is heated to millions of degrees Celsius and it leaves the surface of the Sun in a huge arch, returning some time later. The flares normally occur near sunspots, often along the dividing line between them where there are oppositely directed magnetic forces.
It is the magnetic fields appear to be responsible for the solar flares. When the magnetic field between the sunspots becomes twisted and sheared the magnetic field lines may cross and reconnect with enormous explosive energy. When this occurs an eruption of gases takes place through the solar surface, and it extends several tens of thousands of miles out from the surface of the Sun and follow the magnetic lines of force to form a solar flare. The gases from within the sun start to rise and the area becomes heated even more and this causes the level of visible radiation and other forms of radiation to increase.