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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[10.06] Are All Coronal Loops Heated by Nanoflares?

J.A. Klimchuk, S. Patsourakos, A.R. Winebarger (Naval Research Lab)

Observations from TRACE, SOHO, and Yohkoh have revealed new details of coronal loops that make them more mysterious than ever. One of the biggest puzzles concerns the loop density. Hot (> 2 MK) loops observed by Yohkoh tend to be under dense compared to the predictions of equilibrium theory, while warm (~ 1 MK) loops observed by TRACE and EIT tend to be over dense. Some over dense loops can be explained by steady heating that is concentrated near one or both of the loop legs, but a majority of these loops cannot.

We here consider the possibility that observed loops are comprised of large numbers of unresolved strands that are heated impulsively and randomly by nanoflares. The loops appear quasi-steady even though the individual sub-strands are highly time dependent. When the strands are hot, they cool primarily by thermal conduction and are under dense, but when they are warm, they cool primarily by radiation and are over dense. Since Yohkoh and TRACE are sensitive to different strands, we might expect them to observe the under and over densities that they do.

To evaluate the feasibility of this universal model of coronal loops, we have performed 1D hydrodynamic simulations of impulsively heated strands and compared them with observations from Yohkoh and TRACE. The results are encouraging in many respects, but difficulties remain. In this presentation, we discuss the successes and failures of the model.

This work was supported by NASA and ONR.

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.