34th Solar Physics Division Meeting, June 2003
Session 10 Transequatorial and other Coronal Structures
Oral, Tuesday, June 17, 2003, 9:00am-12:00noon, Auditorium

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[10.05] The Coronal Loop Controversy

J.T. Schmelz (University of Memphis)

Coronal loops are connected with such crucial solar physics questions as the coronal heating problem, the flare trigger, and the effects of solar irradiance on the Earth. Recent results, however, have left the study of these fundamental structures in a somewhat confused state. The solar community cannot currently agree on the answers to some of the most basic questions concerning the physical structure and temporal behavior of loops. Are coronal loops isothermal? The analysis of SXT ratios of broadband coronal loop data show that the temperatures increase from the footpoints to the loop top. But a similar ratio-type analysis of narrowband TRACE or EIT data shows that loops have a constant temperature. Is the coronal heating uniform? Analysis of the same SXT loop data by three different groups has produced three different answers: the heating is (1) uniform; (2) concentrated at the loop footpoints; (3) concentrated at the loop apex. Is the heating episodic? The properties of a set of coronal loops observed with SXT are compatible with steady heating, but those same loops were also compatible with nanoflare heating occurring randomly in thousands of unresolved loop strands. One of the important analysis unknowns to emerge from these controversial results is the effect of 'background subtraction' on loop properties. Proper or improper background subtraction can cause results to flip-flop - from isothermal to multi-thermal, from footpoint heating to apex heating, from steady heating to episodic heating, and vise versa. Here we summarize our background subtraction results for EIT, CDS, and SXT data for both limb and disk loops. Is background subtraction important? Well, yes . . . and no. Solar physics research at the University of Memphis is supported by NASA grants NAG5-9783 and NAG5-12096.

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Bulletin of the American Astronomical Society, 35 #3
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