Physics
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sp51c07v&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SP51C-07
Physics
0654 Plasmas, 7509 Corona, 7519 Flares
Scientific paper
The concept that the solar corona is heated by numerous small flare-like events (nanoflares) is considered. Thus, the hot coronal loop is viewed as an ensemble of high-temperature elemental filaments created within the coronal magnetic field by random impulsive heating events. As a result, these filaments, each of which is at various stages of thermal evolution, have a broad distribution in temperature and density. However, as instantaneous cooling time of the filament has a maximum when conductive and radiation losses become equal, the above distribution is strongly peaked at the corresponding transition temperature. Therefore, the observed temperature of such a loop as a whole obeys the same Rosner-Tucker-Vaiana scaling as was originally derived for a simple loop in a steady state thermal equilibrium. It is shown how this approach allows to predict various signatures of X-ray coronal loops, in particular, dependence of the filling factor, emission measure and thermal energy on the size of the loop and strength of the coronal magnetic field. These integral characteristics of the loop are determined only by its global energy balance, and are not sensitive to specific details of the heating process (such as the energy of individual heating event, spectral index of nanoflates, etc). To probe the latter, we analysed variability of nanoflare heated loops. The aim is to find out how the imposed power-law spectrum of heating events translates into fluctuations in the thermal energy and emission measure of the loop, which can be detected observationally as X-ray and EUV transient brightenings. It was found that the numerically simulated spectrum of these fluctuations typically consists of two different power-law domains. For large intensities the spectral index is close to that of nanoflares, mirroring individual heating events with high energy. However, at lower intensities the spectrum is more flat, as it is caused by interference of several nanoflares.
Jain Rahul
Vekstein Grigory
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