Heliospheric current sheet displacements during the solar cycle evolution

Abstract

The purpose of the present study is to confirm the view of a heliospheric current sheet moving with respect to the solar equator, in relation to the solar cycle phases. For this reason, we have analyzed both observed and high‐accuracy inferred daily interplanetary magnetic field (IMF) polarities between the maxima of solar cycles 18 and 21 (1947–1980). Statistically significant north‐south and “away”‐“toward” differences of the IMF mean sector widths (MSW) have been detected around the solar activity minima while no significant differences have been observed around the maxima or the solar polarity reversals. This peculiar variability of the MSW differences in the solar activity extrema can be finally interpreted by assuming a variable placement of the heliospheric current sheet with respect to the solar equator and the solar cycle phases. Actually, in the epochs of the solar polarity reversal our observations are consistent with a current sheet located symmetrically to the solar equator, almost vertical to it and extending to high heliolatitudes. In the opposite, in the epochs of the solar minima the interpretation of our observations could be due to a current sheet which is southward depressed in the northern but symmetrical in the southern hemisphere. The various placements of the current sheet on both sides of the solar equator in relation to the solar cycle phases, are supposed to originate in north‐south asymmetric solar activity which has been found by several authors to predominate in the solar minima. The MSW differences detected in the last minimum (1975–1977) of the time span under consideration give reasons to venture the prediction that in the solar minima of the time period 1976–1998 the heliospheric current sheet will appear northward depressed in the southern hemisphere but symmetrical in the northern hemisphere. Systematic meridional and high‐latitude observations of both solar wind parameters and IMF patterns would contribute significantly in giving a final answer to the question of possible heliospheric current sheet displacements during the solar cycle evolution.