A 16-moment salar wind model: From the chromosphere to 1 AU

We present a solar wind fluid model extending from the chromosphere to Eart h. The model is based on the gyrotropic approximation to the 16-moment set of transport equations, in which we salve for the density, drift speed, tem perature parallel and perpendicular to the magnetic field, and transport of parallel and perpendicular thermal energy along the magnetic field (heat f lux). The solar wind plasma is created dynamically through (photo) ionizati on in the chromosphere, and the plasma density in the transition region and corona is computed dynamically, dependent on the type of coronal heating a pplied, rather than being set arbitrarily. The model improves the descripti on of proton energy transport in the transition region, where classical hea t conduction is only retrieved in the collision-dominated limit. This model can serve as a "test bed" for any coronal heating mechanism. We consider h eating of protons by a turbulent cascade of Alfven waves in rapidly expandi ng coronal holes. The resulting high coronal proton temperatures lead to a downward proton energy flux from the corona which is much smaller than what classical transport theory predicts, causing a very low coronal density an d an extremely fast solar wind with a small mass flux. Only when some of th e wave energy is forcibly deposited in the lower transition region can a re alistic solar wind be obtained. Because of the poor proton heat transport, in order to produce a realistic, solar wind any viable heating mechanism mu st deposit some energy in the transition region, either directly or via exp licit heating of coronal electrons.