Longitudinal Drifts of Streamers across the Heliospheric Current Sheet

Potential field source surface (PFSS) extrapolations of the photospheric magnetic field provide a qualitatively correct model of the coronal magnetic structure. We show that the magnetic structure provided by PFSS describes a framework within which high-density coronal streamers are distributed. However, the density structures have considerable freedom to drift longitudinally along the magnetic structure. Some caution must therefore be taken when using PFSS models as proxies for the coronal density structure. In particular, while measurements of coronal rotation using PFSS models provide an estimate of the large-scale magnetic structure rotation, they are not valid measurements of the density rotation. Furthermore, attempts to assign a consistent rate of rotation to the electron corona over long time periods are not always valid since the movement is dominated by structural reconfiguration. These conclusions are reached by the application of solar rotational tomography to LASCO C2/Solar and Heliospheric Observatory observations during solar minimum (1996-1997), revealing the changing density structure of the equatorial streamer belt at a height of 4 R sun.