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

[1.31] Boundary Conditions of a Meridional Coronal Hole

B. N. Handy (Montana State University), J. R. Lemen (Lockheed-Martin Advanced Technology Center), D. Moses (U.S. Naval Research Laboratory)

Observational evidence from Skylab suggests that some coronal holes rotate almost rigidly, in contrast to the underlying photospheric plasma which rotates differentially. Wang amp; Sheeley (1996 Science 271, 417 and references therein) suggest these rotational properties are consistent with a nearly current-free coronal field undergoing continual field-line reconnection at the coronal hole boundaries.

If true, this effect may be observable in currently available solar observations. A rigidly rotating coronal hole anchored in an equatorial bipolar magnetic region would in effect "sweep out" a region at the mid-lattitudes, reconnecting with the magnetic terrain on the leading edge boundary and then succumbing back into the background field on the trailing edge. It is not clear how this phenomena takes place, although Kahler and Moses (1990 ApJ 362,728), based on evidence from Skylab, argue that the evolution of the large scale boundary is largely controlled by the evolution of small-scale bright points.

We present a simple model of the evolution of the coronal hole boundary. Assuming a meridional coronal hole extending from the polar hole to an active region near the equatorial plane, we evaluate the rate of magnetic reconnection at the leading and trailing edges based on a nominal level of magnetic field, plasma density, temperature and chromospheric differential rotation rate. We compare this study to observations from EIT and MDI on \itSoHO and SXT on \itYohkoh.

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Program listing for Friday