Flare Activity and Magnetic Helicity Injection by Photospheric Horizontal Motions

Details Flare Activity and Magnetic Helicity Injection by Photospheric Horizontal Motions Flare Activity and Magnetic Helicity Injection by Photospheric Horizontal Motions

Aug 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002apj...574.1066m&link_type=abstract

The Astrophysical Journal, Volume 574, Issue 2, pp. 1066-1073.

Astronomy and Astrophysics

Astronomy

57

Sun: Flares, Sun: Magnetic Fields, Sun: Photosphere

Scientific paper

We present observational evidence that the occurrence of homologous flares in an active region is physically related to the injection of magnetic helicity by horizontal photospheric motions. We have analyzed a set of 1 minute cadence magnetograms of NOAA AR 8100 taken over a period of 6.5 hr by the Michelson Doppler Imager on board the Solar and Heliospheric Observatory. During this observing time span, seven homologous flares took place in the active region. We have computed the magnetic helicity injection rate into the solar atmosphere by photospheric shearing motions and found that a significant amount of magnetic helicity was injected during the observing period. In a strong M4.1 flare, the magnetic helicity injection rate impulsively increased and peaked at the same time as the X-ray flux. The flare X-ray flux integrated over the X-ray emission time strongly correlates with the magnetic helicity injected during the flaring interval. The integrated X-ray flux is found to be a logarithmically increasing function of the injected magnetic helicity. Our results suggest that injection of helicity and abrupt increase of helicity magnitude play a significant role in flare triggering.

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