Speaker
Description
The large-scale configuration of the coronal magnetic field is central to understanding the connection between the Sun and the solar wind, for forecasting space weather, and for interpreting both in situ and remote sensing observations of the corona and beyond. Potential field source surface (PFSS) extrapolations of the observed photospheric magnetic field are invaluable and have been widely used for several decades, but key parameters such as the distance of the source surface lack quantitative constraints. We investigated the use of tomographical maps of the plasma density in the extended corona, gained from coronagraph white light observations, as a constraint on the source surface distance. The values of the radial magnetic field component at the source surface are modified to allow a correlation with the tomographic densities. By adjusting the source surface distance, a maximum correlation is found at a particular distance, or a range of distances. The value of the maximum correlation gives a measure of the effectiveness of the procedure and is dependent on the quality of the tomography and PFSS results. Results for a number of dates over solar cycle 24 show evidence that the source surface distance is likely smallest at solar maximum around 2012 and increases with declining solar activity. Limitations of the method include the use of a purely spherical source surface, and the lack of correspondence between the information contained in the magnetic field data and the plasma density structure, which we try to address.
