Solar Rotation Rate during Solar Activity Cycle 23

We studied the solar rotation rate and its temporal change, using the sunspot data obtained during activity cycle 23 (1996 – 2006). The equatorial rotation rate is nearly the same as in the former cycle 22, while the latitudinal gradient of differential rotation considerably increased. Comparison of our results with others indicates the existence of a long-term periodicity of about eight cycles in differential rotation. In addition, no significant asymmetry in differential rotation between the northern and southern hemispheres during cycle 23 was found. The equatorial rotation rate and the latitudinal gradient of the differential rotation in the period of cycle 23 are approximately constant, except for the initial and final phases in the cycle.