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Session 1 - Chromosphere, Corona, Flares.
Display session, Friday, June 27
Ballroom B, Chair: Charles Kankelborg

[1.47] Measurement and modelling of soft x-ray loop arcades observed by YOHKOH SXT

C. C. Balch (NOAA Space Environment Center), A. J. Hundhausen (NCAR High Altitude Observatory), F. Bagenal (University of Colorado, APAS department)

Yohkoh soft x-ray telescope (SXT) observations of the high temperature corona have motivated a measurement program of soft x-ray loops and systems of such loops that are hypothesized to be a post coronal mass ejection signature. This presumed connection between CMEs and expanding loop arcade systems is based on the picture for CMEs proposed by Kopp & Pneuman (1976) (and other workers as well): specifically that the loop arcade system forms as magnetic field lines that were previously opened by the CME reconnect and heat coronal plasma through the release of magnetic energy at the reconnection point.

We make direct measurements of soft x-ray intensity for a few, well-observed arcade events on the solar limb. Soft x-ray intensity is measured by defining a 2-dimensional region on an x-ray image and summing the intensities from each pixel in the region. This leads to the construction of a soft x-ray intensity light curve. A series of 'light-curve regions' of fixed geometric size are defined at successive heights above the solar limb. Thus we measure soft x-ray intensity from the arcade as a function of time and height.

In order to develop a framework for physical interpretation of these measurements, we developed a model based on our hypothesis and investigated whether the model can explain the data. In particular, we assume that the release of energy is a function of radial distance (from Sun center), and we examine the roles and relative importance of line-of-sight geometric effects, and of finite decay times of individual loops.

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