The Influence of the Chromosphere-Corona Coupling on Solar Wind and Heliospheric Parameters

Abstract

Based on fluid models of the solar wind that extend from the chromosphere out to 1 AU we discuss how the chromosphere-corona coupling affects the ma ss flux, flow speed, and helium abundance of the solar wind in the heliosphere. The downward transport of energy from the corona to the transition region and upper chromosphere can determine the location of the chromosphere-transition region interface and hence the pressure of the corona, and thus strongly influence the solar wind mass flux. In rapidly expanding magnetic field geometries, simulating coronal holes, very little heat is conducted down if only protons are heated in the corona, and in this geometry a reasonable solar wind mass flux is difficult to achieve without additional electron heating in the corona or transition region heating. In a radial geometry downward heat conduction is efficient, resulting in high coronal densities. The rapidly expanding geometry therefore favours a high-speed wind with a low mass flux, and conversely for a radially expanding geometry. In all cases most of the energy deposited in the corona ends up in the solar wind. In a rapidly expanding geometry the helium abundance tends to be low everywhere and the helium flux is limited by the supply from the chromosphere. The radial geometry favours high coronal helium abundances, which may even be close to unity, and the helium flux is then determined by the amount of energy available in the corona to heat helium.