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[88.08] Coronal Heating and the Increase of Coronal Luminosity with Magnetic Flux

R. L. Moore (NASA/MSFC/NSSTC), D. A. Falconer (UAH/MSFC/NSSTC), J. G. Porter, D. H. Hathaway (NASA/MSFC/NSSTC)

We present the observed scaling of coronal luminosity with magnetic flux in a set of quiet regions. Comparison of this with the observed scaling found for active regions by Fisher et al (1998, ApJ, 508, 985) suggests an underlying difference between coronal heating in active regions and quiet regions. From SOHO/EIT coronal images and SOHO/MDI magnetograms of 4 similar large quiet regions, we measure L_Corona and \Phi_Total in random subregions ranging in area from about 4 supergranules [(70,000 km)²] to about 100 supergranules [(0.5 R_Sun)²], where L_Corona is the luminosity of the corona in a subregion and \Phi_Total is the flux content of the magnetic network in the subregion. This sampling of our quiet regions yields a correlation plot of Log(L_Corona) vs Log(\Phi_Total) appropriate for comparison with the corresponding plot from Fisher et al for active regions. For our quiet regions, the mean values of L_Corona and \Phi_Total both increase linearly with area (simply because each set of subregions of the same area has very nearly the same mean coronal luminosity per unit area and mean magnetic flux per unit area), and in each constant-area set the values of L_Corona and \Phi_Total "scatter" about their means for that area. This results in the linear least-squares fit to the Log(L_Corona) vs Log(\Phi_Total) plot having a slope somewhat less than 1. If active regions mimicked our quiet regions in that all large sets of same-area active regions had the same mean coronal luminosity per unit area and same mean magnetic flux per unit area, then the least-squares fit to their Log(L_Corona) vs Log(\Phi_Total) plot would also have a slope of less than 1. Instead, the slope for active regions is 1.2. Given the observed factor of 3 scatter about the least-squares linear fit, this slope is consistent with \Phi_Total on average increasing linearly with area (A) as in quiet regions, but L_Corona on average increasing as the volume (A^1.5) of the active region instead of as the area. This possiblity is reasonable if the heating in active regions is a burning down of previously-stored coronal magnetic energy rather than a steady dissipation of energy flux from below as expected in quiet regions.

This work is supported by NASA, OSS, through its S&HP SR&T and SEC GI programs.

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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.