Flare Activity of the Sun and Variations in its UV Emission During Cycle 24
The flare activity and ultraviolet emission of the sun during its 24th cycle are analyzed. As opposed to cycles 21-23, where the most powerful flares were observed during the decay phase, in cycle 24 the most powerful flares (>X2.7) occurred in the rising phase and at the maximum. Regression fits of the UV indices to the overall radiation level from the sun are substantially different for cycle 24 compared to cycles 21-23. It is found that for the flare of August 9, 2011 (SDO and GOES-15 observations), the flare propagates in a direction from the upper corona to the lower corona in the chromosphere. A study of the N-S asymmetry in the distribution of the flares in cycle 24 reveals a strong predominance of flares in the N-hemisphere in 2011 and in the S-hemisphere in 2014. It is also found that during cycles 23 and 24, the delays in the onset of proton events relative to the onset of the flares that cause them have a distribution with a distinct maximum corresponding to a delay of 2 hours for protons with energies >10 MeV, as well as for those with energies >100 MeV.
KeywordsSun: cycle 24: flares: flare index: variations in UV emission: proton events
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