Rotation-rate variations at the tachocline: An update

After 15 years of GONG and MDI observations of the solar interior rotation, we revisit the issue of variations in the rotation rate near the base of the convection zone. The 1.3-year period seen in the first few years of the observations disappeared after 2000 and has still not returned. On the other hand, the agreement between GONG and MDI observations suggests that variations seen in this region have some solar origin, whether a true rotation-rate change or possibly mere stochastic variation; we present a numerical experiment supporting this contention.