What are Solar Flares?

Solar flares are sudden bursts of solar X-ray and EUV radiation caused by the crossing or restructuring of magnetic field lines near sunspots. When this energetic radiation reaches Earth it enhances the D-region of the ionosphere, causing "fadeout" and/or "radio blackout" events. Flares can last from tens of seconds to several hours.

Solar flares usually occur in active regions on the Sun, marked by strong magnetic fields associated with sunspot groups. The intensity of solar flares is classified based on peak emission in the 0.1 - 0.8 nm spectral band (soft X-rays). NOAA/GOES XRS categorizes flares into different levels: A, B, C, M, and X. Radio blackouts are classified using a five-level NOAA Space Weather Scale, directly related to the flare's max peak in soft X-rays reached or expected. The severity descriptors for radio blackouts are as follows:

• R1 - Minor: Associated with "A" and "B" flares.
• R2 - Moderate: Associated with "M5" flares.
• R3 - Strong: Associated with "X1" flares.
• R4 - Severe: Associated with "X10" flares.
• R5 - Extreme: Associated with "X20" flares.

References:
1. Solar Flares (Radio Blackouts) ^{NOAA / NWS Space Weather Prediction Center}
2. Types of Space Weather Storms
3. Communications blackout ^Wikipedia
4. Radio Blackout ^UNDRR

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