EFFECT OF CORONAL MASS EJECTIONS ON THE STRUCTURE OF THE HELIOSPHERICCURRENT SHEET

The existence of a relatively stable large-scale heliospheric current sheet (HCS) structure near sunspot maximum has recently been questione d [Hundhausen, 1992]. We consider this question here by determining th e effect of coronal mass ejections (CMEs) on the spiral characteristic s of the interplanetary magnetic field (IMF) and on the HCS. In genera l, 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 lifetim e of the HCS structure; (2) the internal structure of IMF sector bound aries 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 characteris tics are maintained, and the calculated sector pattern agrees very wel l with that observed at 1 AU; and (4) the fact that the calculated clo sed field regions correspond to the helmet streamers observed in the F ebruary 16, 1980, solar eclipse confirms the validity of the three-dim ensional 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 interv als when CMEs occur frequently and several coronal helmet streamers al ong the base of the HCS are disrupted or blown out. Ulysses observatio ns at the next sunspot maximum may finally answer the question.