A method to determine the heating mechanisms of the solar corona

One of the paradigms about coronal heating has been the belief that the mea n or summit temperature of a coronal loop is completely insensitive to the nature of the heating mechanisms. However, we point out that the temperatur e profile along a coronal loop is highly sensitive to the form of the heati ng. For example, when a steady state heating is balanced by thermal conduct ion, a uniform heating function makes the heat flux a linear function of di stance along the loop, while T-7/2 increases quadratically from the coronal footpoints; when the heating is concentrated near the coronal base, the he at flux is small and the T-7/2 profile is flat above the base; when the hea t is focused near the summit of a loop, the heat flux is constant and T-7/2 is a linear function of distance below the summit. It is therefore importa nt to determine how the heat deposition from particular heating mechanisms varies spatially within coronal structures such as loops or arcades and to compare it to high-quality measurements of the temperature profiles. We propose a new two-part approach to try and solve the coronal heating pro blem, namely, first of all to use observed temperature profiles to deduce t he form of the heating, and second to use that heating form to deduce the l ikely heating mechanism. In particular, we apply this philosophy to a preli minary analysis of Yohkoh observations of the large-scale solar corona. Thi s 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 implic ation 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 o r at their summits. Unless waves can be shown to produce a heating close en ough to uniform, the evidence is therefore at present for these large loops more in favor of turbulent reconnection at many small randomly distributed current sheets, which is likely to be able to do so. In addition, we sugge st that the decline in coronal intensity by a factor of 100 from solar maxi mum to solar minimum is a natural consequence of the observed ratio of magn etic held strength in active regions and the quiet Sun; the altitude of the maximum temperature in coronal holes may represent the dissipation height of Alfven waves by turbulent phase mixing; and the difference in maximum te mperature in closed and open regimes may be understood in terms of the role s of the conductive flux there.