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The Heating of the Solar Corona View all abstracts by submitter

Eric R Priest   Submitted: 2000-01-11 11:03

One of the paradigms about coronal heating has been the belief that the mean or summit temperature of a coronal loop is completely insensitive to the nature of the heating mechanisms. However, we point out that the temperature profile along a coronal loop is highly sensitive to the form of the heating. For example, when a steady-state heating is balanced by thermal conduction, a uniform heating function makes the heat flux a linear function of distance along the loop, while T7/2 increases quadratically from the coronal footpoints; when the heating is concentrated near the coronal base, the heat flux is small and the T7/2 profile is flat above the base; when the heat is focussed near the summit of a loop, the heat flux is constant and T7/2 is a linear function of distance below the summit. This realisation may act as an incentive to proponents of particular heating mechanisms to determine how the heat deposition varies spatially within coronal structures such as loops or arcades and to observers to deduce the temperature profiles with as low an error as possible. We therefore propose a new two-part approach to try and solve the coronal heating problem, namely first of all to use observed temperature profiles to deduce the form of the heating, and secondly to use that heating form to deduce the likely heating mechanism. In particular, we apply this philosophy to a preliminary analysis of Yohkoh observations of the large-scale solar corona. This gives strong evidence against heating concentrated near the loop base for such loops and suggests that heating uniformly distributed along the loop is slightly more likely than heating concentrated at the summit. The implication is that large-scale loops are heated in situ throughout their length, rather than being a steady response to low-lying heating near their feet or at their summits. Unless waves can be shown to produce a heating close enough to uniform, the evidence is therefore at present for these large loops more in favour of turbulent reconnection at many small randomly-distributed current sheets, which is likely to be able to do so. In addition, we address briefly the questions: why does the coronal intensity reduce by a factor of 100 from solar maximum to solar minimum; why is the temperature maximum in large-scale closed regions about 2.3 MK at an altitude 1.5 Rodot; and why are the corresponding values in coronal holes about 1.5 MK and 1.5 Rodot?

Authors: E. R. Priest, C. R. Foley, J. Heyvaerts, T.D. Arber$^{*}$, D. Mackay$^{*}$, J. L. Culhane$^{+}$ and L.W. Acton

Publication Status: Ap J (submitted)
Last Modified: 2000-01-11 11:03
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