Coronal heating, densities, and temperatures and solar wind acceleration

Abstract

The outflow of coronal plasma into interplanetary space is a consequence of the coronal heating process. Therefore the formation of the corona and the acceleration of the solar wind should be treated as a single problem. The deposition of energy into the corona through some “mechanical” energy flux is balanced by the various energy sinks available to the corona, and the sum of these processes determines the coronal structure, i.e., its temperature and density. The corona loses energy through heat conduction into the transition region and through the gravitational potential energy and kinetic energy put into the solar wind. We show from a series of models of the chromosphere‐transition region‐corona‐solar wind system that most of the energy deposited in a magnetically open region goes into the solar wind. The transition region pressures and the coronal density and temperature structure may vary considerably with the mode and location of energy deposition, but the solar wind mass flux is relatively insensitive to these variations; it is determined by the amplitude of the energy flux. In these models the transition region pressure decreases in accordance with the increasing coronal density scale height such that the solar wind mass loss is consistent with the energy flux deposited in the corona. On the basis of the present study we can conclude that the exponential increase of solar wind mass flux with coronal temperature, found in most thermally driven solar wind models, is a consequence of fixing the transition region pressure.