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Y. Mok (University of California - Irvine), R. Lionello, Z. Mikic, J. Linker (Science Applications International Corp.)
The density-temperature profile of the atmosphere above an active region fundamentally affects its characteristic photon emissions, including UV, EUV and soft X-ray. Measurements made by Yohkoh, SOHO, and TRACE of the bright, magnetic-field aligned, plasma loops partially reveal the possible combinations of local plasma density and temperature of these magnetic structures. We have studied the underlying physics that leads to the unique combination of density and temperature, as well as their spatial dependence, of the plasma that gives rise to the characteristic EM emissions. The physical mechanisms include heat deposition, radiative cooling and the highly anisotropic, highly nonlinear thermal conduction. The 3-D simulation is very demanding on computing resources due the sharp temperature gradient in the lower transition region that ultimately requires a physical resolution of ~10 km in a domain of ~100000 km. We have devised a method to simplify the computation based on the physical assumption that the plasma beta in an active region is sufficiently low that the flows are primarily along the field lines. The 3-D results agree well with a heuristic 1-D loop model for the density- temperature profiles along individual field lines. Using a vector magnetogram of an active region, we have computed the magnetic field for both potential and force-free cases, their respective thermal structures and soft X-ray emissions.
* Work supported by The Sun-Earth Connection Theory Program of NASA.
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.