PRODUCTIVITY OF SOLAR FLARES AND MAGNETIC HELICITY INJECTION IN ACTIVE REGIONS

Abstract

The main objective of this study is to better understand how magnetic\nhelicity injection in an active region is related to the occurrence and\nintensity of solar flares. We therefore investigate magnetic helicity injection\nrate and unsigned magnetic flux, as a reference. In total, 378 active regions\nare analyzed using $SOHO$/MDI magnetograms. The 24-hour averaged helicity\ninjection rate and unsigned magnetic flux are compared with the flare index and\nthe flare-productive probability in next 24 hours following an measurement. In\naddition, we study the variation of helicity over a span of several days around\nthe times of the 19 flares above M5.0 which occurred in selected strong\nflare-productive active regions. The major findings of this study are: (1) for\na sub-sample of 91 large active regions with unsigned magnetic fluxes in the\nrange from 3 to 5 $\\times$ 10$^{22}$ Mx, there is a difference in magnetic\nhelicity injection rate between flaring active regions and non-flaring active\nregions by a factor of 2; (2) the $GOES$ C-flare-productive probability as a\nfunction of helicity injection displays a sharp boundary between\nflare-productive active regions and flare-quiet ones; (3) the history of\nhelicity injection before all the 19 major flares displayed a common\ncharacteristic: a significant helicity accumulation of (3-45)$ \\times$ 10\n$^{42}$ Mx$^2$ during a phase of monotonically increasing helicity over 0.5 to\n2 days. Our results support the notion that helicity injection is important in\nflares, but it is not effective to use it alone for the purpose of flare\nforecast. It is necessary to find a way to better characterize the time history\nof helicity injection as well as its spatial distribution inside active\nregions.\n