Changes in Solar Rotation over Two Solar Cycles

We use helioseismic data from ground- and space-based instruments to analyze how solar rotation has changed since the beginning of solar Cycle. 23 with emphasis on studying the differences between Cycles 23 and 24. We find that the nature of solar rotation is indeed different for the two cycles. While the changes in the latitudinally independent component follows solar-cycle indices, some of the other components have a more complicated behavior. There is a substantial change in the behavior of the solar zonal flows and their spatial gradients too. While the zonal flows in Cycle 24 are weaker in general than those in Cycle. 23, there are clear signs of the emergence of Cycle. 25. We have also investigated the properties of the solar tachocline, in particular, its position, width, and the change (or jump) in the rotation rate across it. We find significant temporal variation in the change of the rotation rate across the tachocline. We also find that the changes in solar Cycle. 24 were very different from those of Cycle. 23. We do not find any statistically significant change in the position or the width of the tachocline.