Abstract

Recently, the surface dierential rotation parameters were found to vary dierently with time for the northern and southern hemispheres of the Sun. Both sunspots and flares strongly suggest that the northern hemisphere rotated considerably faster than the southern during the last three solar cycles, showing a strong north-south asymmetry in solar surface rotation. In order to study the long-term variation of solar surface differential rotation, the location of sunspots during 1877-2009 is analyzed separately in the two hemispheres. The variation of the rotation of the northern hemisphere is found to have an anti-correlation with that of the southern hemisphere and the variation suggests a period of 10-12 cycles.