Two Phases of Helicity Variation Around Major Flares

Details Two Phases of Helicity Variation Around Major Flares Two Phases of Helicity Variation Around Major Flares

Jun 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006spd....37.2201p&link_type=abstract

American Astronomical Society, SPD meeting #37, #22.01; Bulletin of the American Astronomical Society, Vol. 38, p.249

Astronomy and Astrophysics

Astronomy

Scientific paper

We have investigated the magnetic helicity injection rates in three active regions (NOAA 10484, 10486 and 10696) around the times of four X-class flares using the MDI/SOHO magnetograms. In all cases, the total magnetic flux of the individual active region changed little with time, and the helicity variation is directly related to the variation of field line winding. This also justifies our measurement of magnetic helicity injection rates using a local correlation tracking method. Our analysis reveals that there were two distinct phases of helicity variation around those flares. In the first phase that starts a few days before the flare onset, the helicity accumulates at a nearly constant rate. The second phase usually starts 3-12 hours before the flare onset and lasts until 3-20 hours after the flare. During this phase, the helicity injection rate is negligible and the magnitude of helicity remains almost constant or increases only slightly. This characteristic pattern in the helicity evolution may imply a physical link between magnetic winding and flare occurrence, and could be used as an early warning sign of impending flares.

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