X-class flares in the 24th solar activity cycle: Preflare and postflare conditions in the active region: Part 1. Analysis criteria and general comments

We analyzed the data on the flares of the X-ray class X in the 24th solar activity cycle. Several properties of the active regions (their morphological structure, the changes in the structure of the magnetic fields of spots, the evolution dynamics, etc.) were also analyzed with the object of identifying the factors that influence the flare activity of a group the most. In order to gather the maximum amount of experimental data, we used the observational data that cover various levels of the solar atmosphere that were obtained both by terrestrial and space (SOHO, SDO, XRT, Hinode, etc.) telescopes.     

Vertical Electric Currents in Active Regions: Calculation Methods and Relation to the Flare Index

Geomagnetism and Aeronomy - In the scope of the performed work, two problems are solved. The first is the analysis of two existing methods for calculating vertical electric currents, differential...     

Sunspot groups with high flare activity: Specific features of magnetic configuration,morphology, and dynamics

Specific features of the magnetic configuration, morphological structure, dynamics, and evolution of sunspot groups of the current (24th) cycle of solar activity with high flare activity are considered. The gradients of longitudinal magnetic fields at places of δ-configuration are calculated. The main finding is a time delay of 24–30 h between the time when the magnetic field gradient reaches a critical level of 0.1 G/km and the time when the first of powerful flares occurs in the active region. The study is based on data from the SDO and GOES-15 spacecrafts and ground-based solar telescopes (TST-2 at the Crimean Astrophysical Observatory of the Russian Academy of Sciences and the 150-foot telescope at the Mount Wilson Observatory).     

Parameters of Electric Currents in Active Regions with Different Levels of Flare Productivity and Different Magnetomorphological Types

Geomagnetism and Aeronomy - In this paper, the magnetic-field and electric-current parameters are calculated for a sample of 73 active regions (ARs) of solar activity cycle 24 based on...