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Comparison of Two Eruptive Flares

Haimin Wang


We combined, and analyzed in detail, the Halpha and magnetograph data from Big Bear Solar Observatory, full-disk magnetograms from MDI/SOHO, coronagraph data from LASCO SOHO, FeXII 195A data from EIT/SOHO and Yohkoh SXT data of the M6.8 flare of April 29, 1998 in NOAA Region 8375 and the M8.4 flare of November 5, 1998 in NOAA Region 8384.

Those two flare have remarkable similarities:

(1) Partial halo CMEs were observed for both events. For the April 29, 1998 event, even though the flare occurred in the S-E of the disk center, the ejected material predominantly moved cross the equator, and the central part of the CME occurred in the N-E limb. The direction in which the cusp points in the post-flare SXT images determines the dominant direction of the CMEs. (2) Coronal dimming was clearly observed in EIT FeXII 195A for both, but not observed in Yohkoh SXT for either event.  Dimming started two hours before onset of flares, indicating large scale coronal restructuring before both flares. (3) No global or local photospheric magnetic field change was detected from either event; in particular, no magnetic field change was found in the dimming areas. (4) Both events lasted several hours, and, thus, could be classified as long duration events (LDEs). However, they are different in the following important aspects:

For the April 29, 1998 event, the flare and the CMEs are associated with an erupting filament in which the two initial ribbons were well-connected,  and then gradually separated. SXT pre-flare image shows the classical S- shape sheared configuration (sigmoid structure). For the November 5,  1998 event, two initial ribbons were well separated, and the SXT pre-flare image shows the interaction of at least two loops. In addition, no filament eruption was observed.

We conclude that even though those two events resulted in the similar coronal consequences, they are due to two distinct physical processes:  eruption of sheared loops and interaction of two loops.

  Organization: Big Bear Solar Observatory
     Telephone: 973-596-5781
           Fax: 973-596-3617
        e-mail: haimin@solar.njit.edu
       Address: Physics Department
   New Jersey Institute of Technology
   Newark, NJ 07102
         Paper: Comparison of Two Eruptive Flares

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Curators: Robert Candey, Alex Young, Tamara Kovalick

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