Time variations in solar activity.

Abstract

Long-term variations in the height of solar maxima and in the relative spottedness of the northern and southern solar hemispheres are considered. Mean sunspot numbers in the present solar cycle are found to be similar to those in cycles with maxima in 1937, 1917, 1860, and 1769. Time variations within the 11-year cycle are considered. It is pointed out that all solar latitudes and longitudes do not attain maximum levels of activity at the same time. Furthermore, the course of solar activity as measured by sunspot number and 2800 MHz flux is seldom smooth but appears to advance by series of pulses or episodes. Study of the declining branches of solar cycles 12 through 19 suggests that there will be 5 to 6 primary fluctuations of activity on the declining branch of cycle 20 in the years 1970.5-1975. At least half of these pulses can be expected to include significantly flare-rich centers of activity.