Funnels and the Origin of the Solar Wind

Abstract

A short overview of the historic development of the idea of a funnel shaped geometry in the lower solar atmosphere (chromosphere, transition region and lower corona) is presented as an introduction. It is followed by a short presentation of the early prediction of solar wind expansion by Parker. A large number of observations and theoretical studies have since helped to refine this basic picture. We know the wind is driven by heating of the corona. Modelling has shown that in a magnetically “open” corona most of the energy deposited is lost in the solar wind. Hence the wind is not merely an “evaporating tail” of a hydrostatic plasma, rather the corona and wind should be regarded as one tightly coupled system. An overview of observations that are crucial for our present understanding of the wind is given. It is followed by a discussion of the energy flow between corona and chromosphere which determines the solar wind mass flux. Once the basic physical understanding of the solar wind is established we will present some recent studies which introduce funnel type geometries and investigate their effect on the properties of the solar wind.