Effect of coronal mass ejections on the structure of the heliospheric current sheet

Abstract

The existence of a relatively stable large‐scale heliospheric current sheet (HCS) structure near sunspot maximum has recently been questioned [Hundhausen, 1992]. We consider this question here by determining the effect of coronal mass ejections (CMEs) on the spiral characteristics of the interplanetary magnetic field (IMF) and on the HCS. In general, CMEs do not have long‐term effects on the location of the HCS. The evidence shows that (1) the coronal streamer belt locally disrupted or blown out by CMEs reforms in a time interval shorter than the lifetime of the HCS structure; (2) the internal structure of IMF sector boundaries is temporarily changed during the passage of the interplanetary counterpart of CMEs; (3) even in the Carrington rotation just 1 month after the sunspot maximum of solar cycle 21 the IMF spiral characteristics are maintained, and the calculated sector pattern agrees very well with that observed at 1 AU; and (4) the fact that the calculated closed field regions correspond to the helmet streamers observed in the February 16, 1980, solar eclipse confirms the validity of the three‐dimensional model even at high activity, giving additional confidence in the predicted HCS location. The rapid reformation of disrupted helmet structures may explain the existence of a structured HCS during intervals when CMEs occur frequently and several coronal helmet streamers along the base of the HCS are disrupted or blown out. Ulysses observations at the next sunspot maximum may finally answer the question.