The most violent super-active regions in the 22nd and 23rd cycles

Abstract

We survey 14 super-active regions (SARs) in the 22nd cycle and 15 SARs in the 23rd cycle. Each produced major flares and major solar storms. Among them, the 25 most violent super active regions (VSARs) are selected based on five parameters: the largest area of sunspots, X-ray flare index (XRI), 10.7 cm radio flux, proton flux and geomagnetic A p index. In order to understand the VSARs, we have investigated a few key magnetic properties of those regions, i.e., net magnetic flux, tilt angle and force-free parameter αbest. The following results are found: (1) Most VSARs (84%) in our samples have net magnetic flux greater than 1021 Mx, implying that those are seriously unbalanced flux regions. Unbalanced flux active regions probably provide a nest to relate the small-scale to the large-scale magnetic field. (2) Most of the VSARs (68%) are of abnormal magnetic structure, violating the Hale–Nicholson Law. For most of the normal VSARs, the tilt angles are larger than 40°. 84% of the VSARs follow the hemispheric helicity rule. Generally, they have large magnetic twist and writhe helicity. (3) We also enlarge our samples to study the locations of VSARs by adding the top 10 of the major flares, proton events and severe magnetic storms from 1976 to 2001. It is found that 77% in our 30 samples of VSARs were preferentially located in 4 longitude bands, i.e., l c=80°±15° l c=170°±15° l c=260°±15° and l c=350°±15°. The interval of those longitude bands is roughly 90°. From the above results, we suggest that there probably is a special magnetic environment in the sub-photosphere of the four longitude bands where it is preferred to produce abnormal and complex active regions which easily produce major flares and major solar storms. Area, magnetic class, net magnetic flux, Carrington longitude and tilt angle of an active region may serve to predict likelihood of the active region producing hazarded space weather.