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The scalings of the coronal plasma parameters with the mean photospheric magnetic field: The long-term evolution of AR 7978 View all abstracts by submitter

Pascal Demoulin   Submitted: 2002-12-05 08:20

We analyze the evolution of the fluxes observed in X-rays and correlate them with the magnetic flux density in active region NOAA 7978 from its birth throughout its decay, for five solar rotations. We use SoHO/MDI data to derive magnetic observables, together with Yohkoh/SXT and Yohkoh/BCS data to determine the global evolution of the temperature and the emission measure of the coronal plasma at times when no significant brightenings were observed. We show that the mean X-ray flux and derived parameters, temperature and emission measure (together with other quantities deduced from them, such as the density and the pressure), of the plasma in the AR follow power-law relationships with the mean magnetic flux density (ar{B}). The exponents (b) of these power-law functions (a ar{B}b) are derived using two different statistical methods, a classical least-squares method in log-log plots and a non-parametric method, which takes into account the fact that errors in the data may not be normally distributed. Both methods give similar exponents, within error bars, for the mean temperature and for both instruments (SXT and BCS); in particular, b stays in the range [0.27,0.31] and [0.24,0.55] for full resolution SXT images and BCS data, respectively. For the emission measure the exponent b lies in the range [0.85,1.35] and [0.45,1.96] for SXT and BCS, respectively. The determination of such power-law relations, when combined with the results from coronal heating models, can provide us with powerful tools for determining the mechanism responsible for the existence of the high temperature corona.

Authors: van Driel-Gesztelyi L., Demoulin, P., Mandrini C.H., Harra, L., Klimchuk, J.A.
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Publication Status: ApJ, preprint, in press
Last Modified: 2002-12-05 08:20
Go to main E-Print page  Astrophysics 2002 (Section 2: Solar Physics)  Testing coronal heating models: The long-term evolution of AR 7978  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

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