Magnetic Shear in Two-ribbon Solar Flares

Details Magnetic Shear in Two-ribbon Solar Flares Magnetic Shear in Two-ribbon Solar Flares

May 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...210.3702s&link_type=abstract

American Astronomical Society Meeting 210, #37.02; Bulletin of the American Astronomical Society, Vol. 39, p.151

Astronomy and Astrophysics

Astrophysics

Scientific paper

To study shear motion of the footpoints in solar flares, we selected 50 X- and M- class two-ribbon flares observed by TRACE (in 1998-2005) as our data sample. We found that: 1) 86% (43 out of 50) of these flares show both strong-to-weak shear change of footpoints and ribbon separation. Shear motion of footpoints is thus a common feature in two-ribbon flares; 2) the initial and final shear angles of the footpoints in this type of flare are mainly in the range from 50° to 80° and 15° to 55°, respectively; 3) in 10 out of the 14 events with both measured shear angle and corresponding hard X-ray observations, the cessation of shear change is 0-2 minutes earlier than the end of the impulsive phase. This may suggest that the change from impulsive to gradual phase is related to magnetic shear change. We then selected 20 flares with measured shear angles and corresponding CMEs from our data sample. For these flares, we found that the magnetic flux and change of shear angle show comparably strong correlations with the peak flare flux and CME speed, while the intial shear angle does not. This result indicates that the intensity of flare/CME events may depend mainly on the released magnetic free energy rather than the total magnetic free energy stored prior to the eruption. After a successful launch last September, Hinode (Solar-B) caught two X-class solar flares, which occurred in AR 10930 on Dec 13 and 14, 2006. Using these new datasets (Hinode/XRT, Hinode/SOT, TRACE, and SOHO/MDI), we carried out a study of the evolution of the sheared magnetic fields involved in these flares, and some preliminary results will also be presented. The TRACE analysis was supported at Smithsonian Astrophysical Observatory by a contract from Lockheed Martin.

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