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Do EUV Nanoflares Account for Coronal Heating? View all abstracts by submitter

Markus J Aschwanden   Submitted: 1999-10-06 21:04

Recent observations with EUV imaging instruments such as SoHO/EIT and TRACE have shown evidence for flare-like processes at the bottom end of the energy scale, in the range of Ethapprox 1024-1027 erg. Here we compare these EUV nanoflares with soft X-ray microflares and hard X-ray flares across the entire energy range. From the observations we establish empirical scaling laws for the flare loop length, L(T) propto T, the electron density, n_e(T) propto T^2, from which we derive scaling laws for the loop pressure, p(T) propto T^3, and the thermal energy, Eth propto T^6. Extrapolating these scaling laws into the {sl picoflare regime} we find that the pressure conditions in the chromosphere constrain a height level for flare loop footpoints, which scales with heq(T) propto T-0.5. Based on this chromospheric pressure limit we predict a lower cutoff of flare loop sizes at Lminlapprox 5 Mm and flare energies Eminlapprox 1024 erg. We show evidence for such a rollover in the flare energy size distribution from recent TRACE EUV data. Based on this energy cutoff imposed by the chromospheric boundary condition we find that the energy content of the heated plasma observed in EUV, SXR, and HXR flares is insufficient (by 2-3 orders of magnitude) to account for coronal heating.         and Transition Region'', Monterey, California, 24-27 August 1999),        Solar Physics, Dec issue, in press.

Authors: Aschwanden,M.J.

Publication Status: (Contribution to the TRACE workshop ``Physics of the Solar Corona
Last Modified: 1999-10-06 21:04
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