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Session 33 - Dynamics of Solar Magnetic Fields.
Oral session, Tuesday, June 11
It is well known that large-scale soft X-ray arcades form and grow in the aftermath of coronal mass ejections. This phenomenon is usually interpreted as evidence for magnetic reconnection occurring at progressively greater heights along the vertical current sheet that is created when the coronal field is stretched open by the eruption. Closed magnetic loops are formed and heated by the reconnection, and they subsequently fill with hot, dense plasma evaporated from the chromosphere. The loops then cool and fade from view, but as they do, new hot loops are created above. In this way the arcade slowly grows, shell by shell.
This picture is very appealing and seems to agree qualitatively with many aspects of the observations, but is it correct? We have studied the disk event of 1993 Jan 26 and found a startling inconsistency: the rate at which the arcade plasma is observed to be heated is two orders of magnitude smaller than the rate at which energy is expected to be extracted from the magnetic field. Is the standard interpretation fundamentally wrong? We suggest that it is essentially correct, but that only a small fraction (\sim 1%) of the open magnetic field actually reconnects. We discuss a possible reason for this involving 3D effects, as well as the interesting consequences that it has for the detailed magnetic structure of fully formed coronal arcades.
Program listing for Tuesday