On the seasonal distribution of sunspot frequency

Using the Zurich sunspot data, the seasonal distribution of all sunspot-groups and of all new-formed groups from 1938 to the last solar minimum in 1976 was investigated. It is shown that there exist different distributions for the northern and southern solar hemisphere with maxima in the third and second quarter of the years, respectively, and seasonal differences in the north-south asymmetry. These results confirm the presumption of an influence of interstellar matter on solar activity. (Auth.)