Evolution of Coronal Relative Magnetic Helicity and Current Helicity in NOAA Active Region 11158
Abstract
The evolution of relative magnetic helicity contained in an active region is a crucial ingredient to describe the complexity in solar atmosphere. In this paper we present the temporal evolution of relative magnetic helicity (Hr) in NOAA active region 11158 during a 4-day period of February 12-15, 2011. The photospheric vector magnetograms of the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamic Observatory (SDO) are used as the boundary conditions to extrapolate the three-dimensional (3D) non-linear force-free (NLFF) coronal magnetic field, based on which Hr inside the 3D coronal volume is deduced. A bump pattern in Hr prior to two major flares is noted and may be a precursor of major flares. We compare the temporal variation of Hr with that of the accumulated amount of helicity injected through the photosphere that is inferred independently by tracking the apparent motion of magnetic footpoints at the photosphere from a line-of-sight HMI magnetogram series. The good consistency between Hr and the injected helicity suggests that the helicity is generated largely below the photosphere and is well conserved from the subsurface into the corona. In addition, the altitude-time diagram of the average unsigned current helicity displays a clear propagation pattern over two days prior to the X2.2 flare of February 15, with an average propagation rate of 36 m/s. The propagation is synchronous with the emergence of magnetic flux, and indicative of a gradual energy buildup for the flares.
- Publication:
-
American Astronomical Society Meeting Abstracts #220
- Pub Date:
- May 2012
- Bibcode:
- 2012AAS...22041102J