Solar Physics Division Meeting 2000, June 19-22
Session 1. Helioseismology, Magnetic Fields, Chromosphere and Transition Region
Display, Chair: C. U. Keller, Monday-Thursday, June 19, 2000, 8:00am-6:00pm, Forum Ballroom

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[1.44] Observation and Theory of Coronal Loop Structure

J.A. Klimchuk, S.K. Antiochos (Naval Research Lab.), D. Norton (High Performance Fortran Associates), J.A. Watko (Johns Hopkins Univ.)

We have carefully examined 43 soft X-ray loops observed by Yohkoh and 24 EUV loops observed by TRACE and find that the large majority have a nearly uniform thickness. This implies that: 1. the magnetic field in these loops expands with height much less than standard coronal models would predict; and 2. the shape of the loop cross section is approximately circular. We have investigated whether these surprising results can be explained by locally enhanced twist in the field, so that observed loops correspond to twisted coronal flux tubes. Our approach is to construct numerical models of fully three-dimensional force-free magnetic fields. To resolve the internal structure of an individual loop embedded within a much larger dipole configuration, we use a nonuniform numerical grid of size 609 x 513 x 593, the largest ever applied to a solar problem, to our knowledge. Our models indicate that twist does indeed promote circular cross sections in the corona, even when the footpoint cross section is irregular. However, twist does not seem to be a likely explanation for the observed minimal expansion with height.

This work was supported by the NASA Sun-Earth Connection Theory and Guest Investigator Programs.

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