The Open Magnetic Flux of the Sun. I. Transport by Reconnections with Coronal Loops

Abstract

The magnetic field of the Sun includes a component that opens into and creates the heliospheric magnetic field, the so-called open magnetic flux of the Sun. Open flux is transported along the solar surface by random convective motions in the photosphere and also by reconnection with coronal loops and the subsequent displacement of the open field lines. A model is developed to describe the interactions through reconnection of open magnetic field lines and smaller coronal loops on the quiet Sun. The displacement of open field lines by reconnection with such loops can be described as a diffusive process, and the model yields the appropriate diffusion coefficient. The model also relates the total diffusive transport of open flux, as a result of reconnection with loops and random convective motions, to a basic solar parameter, the rate of emergence of magnetic flux per unit surface area. This in turn provides an explanation for the formation of coronal holes: accumulations of open flux. The diffusion process will tend to accumulate open flux into regions where the rate of emergence of new magnetic flux is a local minimum. It is also shown that the parameters used in this model are consistent with and can interrelate a variety of different observations. This work serves as the basis for subsequent papers in which the distribution of open magnetic flux on the Sun and its evolution during the solar cycle is determined, and the transport of open magnetic flux is related to the heating and acceleration of the solar wind.