The phase shift between the hemispheres in the solar activity cycle

Abstract

The shift between the solar activity cycles in the northern and southern hemispheres of the Sun is studied using data on sunspot number and area. The data obtained are compared with archival information on episodes of appreciable solar-cycle asymmetry. The small phase shift between recent activity cycles in the northern and southern solar hemispheres differs considerably from the shift for episodes of appreciable deviations from dipolar symmetry in the sunspot distribution detected with various degrees of confidence in archival astronomical data from the 17th–19th centuries. The current time shift between the hemispheres is insignificant, about 6–7 months. This shift has changed its sign twice in recent solar history; this probably corresponds to more or less periodic variations with a timescale close to the duration of the Gleissberg cycle.