Conductive damping of coronal motions

Abstract

Time‐dependent motions in the solar corona are subject to modification through conductive transport of thermal energy away from compression regions and into rarefaction regions. The evolution depends on how the energy is introduced—by an essentially thermal perturbation or by a density perturbation. The net effect of thermal conduction is to convert local kinetic energy in the transient into widely distributed thermal energy, which then may in turn be partially converted into kinetic energy of the bulk flow. Local motion in the transient is thereby damped. These effects are modeled here using a numerical solution of the time‐dependent solar wind equations for single‐fluid thermally conductive flow. The simulations of transient phenomena are made for ordinary collisional thermal conduction and compared with similar simulations done using polytropic flow. Between one and five solar radii, the gross character in the two cases is very similar. However, there are effects with thermal conduction that cannot be modeled with polytropic flow, illustrated here by temperature and velocity forerunners and a delayed and large‐amplitude trailing velocity low. If thermal conduction is artifically inhibited by simple reduction of the thermal conduction coefficient, relative velocity amplitudes remain larger in approximate proportion to the amount the coefficient is reduced.