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Today’s
Visible Sunspots May Trigger X-Ray Flares
Magnetic Classification of Visible Sunspots
Flare Hazard of Solar Active Regions
Active Regions &
Heliophysic Event Database
Space Weather Updates by Kevin Gibeau, VE3EN
X-Ray Flares Increase Daytime D-Region Absorption
Real-Time Additional D-Region Absorption
HF Propagation OverviewFlares originating from active solar regions may increase the power flux of X-rays up to a million times. The intensity of the solar X-ray power flux is expressed on a logarithmic scale with a letter indicator (A, B, C, M or X) followed by a digit. As X-rays are electromagnetic waves, Earth-directed X-rays reach our planet in eight minutes time. X-ray radiation is highly ionising and will penetrate the ionosphere deeply. X-rays from solar flares will increase the ionisation of the D-layer which, at Earth’s daytime side, will become more absorptive to HF signals. The lower HF spectrum will be most attenuated. The severity of such events is expressed from R1 to R5 on NOAA’s radio blackout scale.
Solar flares also produce energetic particles. Contrary to X-rays, these particles require hours, not minutes, travelling through interplanetary space to reach Earth. If the incoming flux of energetic particles is high, the delayed effect is polar cap absorption (PCA). When this happens, it is also depicted above the poles on the real-time D-layer absorption chart. PCA is further discussed in the section about the geomagnetic effects of the solar particle wind.
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