Structure of the maximum phase of solar cycles 21 and 22

A distinctive peak and gap structure in a number of solar indices was observed in the maximum phase of solar cycles 21 and 22. The effect became even more prominent after separating the northern and southern solar hemispheres. In cycle 21 the multi-peaked structures observed in the two solar hemispheres were not synchronous and their sum resulted in the rather shallow two-peaked solar maximum for the parameters taken over the whole solar disk. In cycle 22 there were only double peaks in each hemisphere which were rather synchronous. Examination of solar activity in the northern and southern hemispheres has shown that the structured maximum appears to be due to the superposition of two quasi-oscillating processes with characteristic time-scales of 11 years and of 1–3 years (quasi-biennial oscillations). The absolute amplitude of the quasi-biennial oscillations depends on the 11-year cycle phase and reaches its maximum at the maximum of the 11-year cycle. This explains the occurrence of a double- or triple-peak structure in the solar maximum phase.