THE LONG-TERM HEMISPHERIC SUNSPOT ACTIVITY

Abstract

Sunspot activity is usually represented by either sunspot numbers (SN) or sunspot areas (SA). The smoothed monthly mean SA and SN in the northern and southern hemispheres from 1945 January to 2008 March are used to investigate the characteristics of long-term hemispheric sunspot activity. Although sunspot activity (SA and SN) is found to begin one month earlier in the northern hemisphere than in the southern hemisphere on the average of the considered time interval, the shift is so small that no long-term systematic phase shift is statistically acceptable as a first-order effect, as suggested by White & Trotter. Sunspot activity never peaks at the same time in the two hemispheres. Although the Schwabe cycle appears in hemispheric sunspot activity, its period length slightly varies during the considered time interval and seems to be longer in the southern hemisphere than in the northern hemisphere on the average. Sunspot activity is asymmetrically distributed in the hemispheres, but the largest hemispheric diversity usually does not appear around the maximum time of a cycle. The diversity of SA, respectively, in the northern and southern hemispheres runs on the Sun similarly and synchronously as the diversity of SN does. Sunspot activity is slightly asynchronous in the hemispheres.