Rotation rate of high-latitude sunspots

Abstract

Rotation rate of 19 high latitude (28–44°) short-lived sunspots collected in 1978–1979 are compared with Newton and Nunn's (1951) recurrent spots rate. To reduce the effect of proper motion in spots of new regions, our measurements start only when the spots have matured or very nearly so. Compared with the expression ω = 14.38−2.96 sin² φ derived from 1934–44 data by Newton and Nunn, our results show a slightly lower differential rotation in the 28–40° zone. They are in better agreement with the Greenwich average results of the five solar cycles beginning 1878: ω = 14.37−2.60 sin² φ.