Coronal Heating and Photospheric Turbulence Parameters: Observational Aspects

Abstract

In this study, the soft X-ray luminosity of the solar corona, measured by the Yohkoh spacecraft for 104 well-developed and decaying active regions, is compared to the magnetic field parameters determined from SOHO MDI high-resolution magnetograms. We calculate and compare (1) two area-independent characteristics of the magnetic field: the index (α) of the magnetic power spectrum, E(k)~k^-α, and the magnetic energy dissipation rate (ɛ¯/η), which is a proxy for the energy of random footpoint motions induced by turbulent convection in the photosphere and below; and (2) four area-independent parameters of the soft X-ray emission: the area-normalized flux in Yohkoh Al.1 and AlMgMn channels, and the emission measure and temperature of the coronal plasma. Here we report that the area-normalized soft X-ray flux correlates with both the power index α (Pearson correlation coefficient ρ=0.72/Al.1 and 0.73/AlMgMn) and the magnetic energy dissipation rate ɛ¯/η (ρ=0.68/Al.1 and 0.70/AlMgMn). Also, both magnetic parameters are well-correlated with the logarithm of the emission measure (ρ=0.72) and the logarithm of temperature [ρ=0.59/α and 0.63/(ɛ¯/η)]. Our results present strong observational support to those coronal heating models that rely on random footpoint motions as an energy source to heat the corona above active regions.