Study of Magnetic Helicity Injection in the Active Region NOAA 11158 Associated with the X-class Flare of 2011 February 15

Details Study of Magnetic Helicity Injection in the Active Region NOAA 11158 Associated with the X-class Flare of 2011 February 15 Study of Magnetic Helicity Injection in the Active Region NOAA 11158 Associated with the X-class Flare of 2011 February 15

May 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011spd....42.2227p&link_type=abstract

American Astronomical Society, SPD meeting #42, #22.27; Bulletin of the American Astronomical Society, Vol. 43, 2011

Astronomy and Astrophysics

Astronomy

Scientific paper

The main objective of this study is to examine a long-term (a few days) precondition and a trigger mechanism for an X2.2 flare peaking at 01:56 UT on 2011 February 15 in GOES soft X-ray flux. For this, we investigated the variation of magnetic helicity injection through the photospheric surface of the flare-productive active region NOAA 11158 during (1) the long-term period of February 11 to 15 with a 1-hour cadence and (2) the short-term period of 01:26 to 02:10 UT on February 15 with a 45-second cadence. The helicity injection was determined using line-of-sight magnetograms with high spatial and temporal resolution taken by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). As a result, we found two characteristic phases of helicity injection related to the X2.2 flare. A large amount of positive helicity was first injected over 2 days with a phase of monotonically increasing helicity. And then the flare started simultaneously with a significant injection of the opposite (negative) sign of helicity around the flaring magnetic polarity inversion line. This observational finding clearly supports the previous studies that there is a continuous injection of helicity a few days before flares and a rapid injection of the helicity in the opposite sign into an existing helicity system triggers flares.

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