Evolution of magnetic field twist and tilt in active region NOAA 10930

Abstract

Magnetic twist of the active region has been measured over a decade using photospheric vector field data, chromospheric Hα data, and coronal loop data. The twist and tilt of the active regions have been measured at the photospheric level with the vector magnetic field measurements. The active region NOAA 10930 is a highly twisted emerging region. The same active region produced several flares and has been extensively observed by Hinode. In this paper, we will show the evolution of twist and tilt in this active region leading up to the two X-class flares. We find that the twist initially increases with time for a few days with a simultaneous decrease in the tilt until before the X3.4 class flare on December 13, 2006. The total twist acquired by the active region is larger than one complete winding before the X3.4 class flare and it decreases in later part of observations. The injected helicity into the corona is negative and it is in excess of 1043 Mx2 before the flares.