Solar activity and the solar wind.

The availability of in situ solar wind observations from the complete sunspot cycle 20 (1964-1976) suggests an examination of the changes in the character of the solar wind related to the solar cycle and comparison of these observed changes with those expected from earlier studies of solar-terrestrial physics. In many ways the observations correspond to these expectations; flare-associated shock waves were probably most important near sunspot maximum, while long-lived streams of high-speed wind, now known to originate in coronal holes, were clearly most important in the declining years of the cycle. However, one important pattern of deviation from the expected behavior must be emphasized. The largest elevations of solar wind speed and the highest level of geomagnetic activity, associated with coronal holes and long-lived streams occurred very late in the cycle rather than near sunspot maximum. The implications of this 'anomalous' behavior are not well understood.