Solar wind speed variations: 1962-1974

Abstract

An analysis of solar wind speed variations, with particular emphasis on changes associated with the advance of the solar activity cycle, has been completed for the period extending from 1962 through 1974. Stable, large amplitude (peak to trough greater than or equal to 350 km s−1) streams were most commonly observed in years of declining and near-minimum solar activity. The presence of these streams significantly affects long-term averages of the solar wind speed, the yearly average flow speed being highest near solar minimum. When they are present, stable streams tend to recur at intervals of 27.1 days; this recurrence period is comparable to most estimates of the rotation period of equatorial regions of the sun as seen from the earth. A comparison of the observed stream structure with the occurrence of interplanetary magnetic field sector boundaries reveals that most high-speed streams were unipolar during this 13-year interval and that successive streams often had the same, rather than opposite, polarities, in substantial agreement with earlier more limited studies.