ar097.sterling06 Posted: 1-Sep-96 Updated: Events specified: AR 7981
A. C. Sterling, T. Watanabe.
Since the Bragg crystal spectrometer (BCS) on Yohkoh is a full-Sun instrument, it can be used to study individual active regions only when such regions are alone on the Sun. Activity on the Sun has reduced to a low enough level in recent months to allow detailed spectral analysis of active regions using BCS. Such studies can be effectively carried out using BCS's SXV channel, which is sensitive to plasmas in the 3--10 MK range. During July 1996, a prominent active region, AR 7981, appeared on the Sun and persisted for at least one full solar rotation. When this region passed to the far side of the Sun beginning around 14 July, there was a large drop in soft X-ray flux as recorded by GOES and the BCS SXV channel. There was a correspondingly large flux increase when the region reappeared on the solar cast limb some ten days later. Just after the region's disappear and just cefore its reappearance, the soft X-ray flux was at intermediate values. This flux originated from the upper coronal portion of the active region, since the lowest parts of the region were occulted by the solar limb at those times. We intend to analyze BCS SXV spectra from those times in order to determine the spectral properties (including electron temperature and non-thermal velocities) of the upper coronal portions of the active region. We will compare our BCS results with images from SXT in an attempt to set limits on some physical properties of soft X-ray loops.