The scalings of the coronal plasma parameters with the mean
photospheric magnetic field: The longterm evolution of AR 7978 

Pascal Demoulin Submitted: 20021205 08:20
We analyze the evolution of the fluxes observed in Xrays 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 Xray 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 powerlaw relationships
with the mean magnetic flux density (ar{B}). The exponents
(b) of these powerlaw functions (a ar{B}^{b}) are derived
using two different statistical methods, a classical leastsquares
method in loglog plots and a nonparametric 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 powerlaw 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 DrielGesztelyi L., Demoulin, P., Mandrini C.H., Harra, L., Klimchuk, J.A.
Projects:

Publication Status: ApJ, preprint, in press
Last Modified: 20021205 08:20


