Nonlocal thermal conduction in hydrodynamic loop flare models

Summary  We study the limits of applicability of the Spitzer-Harm thermal conductivity in models of flaring solar «loop» structures. We show that the electron mean free path in the flaring atmosphere substantially exceeds the bound imposed on it by the linearized theory by which thermal conduction is classically described. In order to nevertheless permit the study of such flaring phenomena, we apply a nonlocal formutation of thermal heat conduction that allows for long electron mean free paths, especially for the most energetic electrons, in this case, we find that the thermal heat flux is carried considerably farther from the corona to the chromosphere. As a consequence, we are able to show that an appropriate treatment of thermal conduction in such atmospheres will lead to a cooler corona, a chromosphere whose heating is somewhat more dominated by thermal conduction from the corona, and a transition region with less steep gradients than those obtained with models based on the standard Spitzer-Harm thermal conductivity.