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Session 70 - Solar Flares and Ejections.
Display session, Thursday, June 13
Tripp Commons,
Some CME models involve the opening of previously closed magnetic field lines as the plasma erupts through the lower corona. However, the identification of observational signatures of this process has proven illusive. We report on Yohkoh/SXT observations of large-scale arcade events which reveal the dimming, or depletion, of coronal material above the bright long-duration arcade region. Viewed in video form, the impression is of an opening up and evacuation of a local portion of the lower corona. We interpret this as the process of field line opening in the initial phase of a CME and, therefore, as the first direct signature of the mass ejection in soft X-rays. The dimming appears as a reduction of the soft X-ray intensity by about a factor of 2-3. We are studying several events of this type which reveal different aspects of the geometry and kinematics of this process. Highly structured loops can be seen expanding in the dimming regions of some events and can be used to characterize the velocity field of the initial CME expansion.
