Cowling resistivity and Joule dissipation in solar atmosphere

Abstract

Joule dissipation rates in the magnetic flux tubes at different heights of the solar atmosphere, from the photosphere to the corona, are studied. It is assumed that the generation of electric currents is caused by convective motions at the photospheric foot-points of the flux tubes. It is shown that the role of ion-atom collisions in the Joule dissipation and solar plasma heating is decisive. The Cowling resistivity exceeds the classical (Spitzer) resistivity not only in the weakly ionized layers of the atmosphere but also in the corona with the relative density of the neutral atoms of about 10 −7 cm −3 if the electric currents are I ≥ 2×10 8 A. As an illustration of the altitude dependence of the Cowling resistivity for different magnitudes of the electric current, we applied the atmospheric model developed by Avrett and Loeser [1]. We have shown that the maximal dissipation occurs in the transition region. The role of Cowling resistivity in Joule dissipation increases with the filamentation of magnetic flux tubes.