Dynamic variations at the base of the solar convection zone

We have detected changes in the rotation of the sun near the base of its co nvective envelope, including a prominent variation with a period of 1.3 yea rs at Low latitudes. Such helioseismic probing of the deep solar interior h as been enabled by nearly continuous observation of its oscillation modes w ith two complementary experiments. Inversion of the global-mode frequency s plittings reveals that the Largest temporal changes in the angular velocity Omega are of the order of 6 nanohertz and occur above and below the tachoc line that separates the sun's differentially rotating convection zone (oute r 30% by radius) from the nearly uniformly rotating deeper radiative interi or beneath. Such changes are most pronounced near the equator and at high L atitudes and are a substantial fraction of the average 30-nanohertz differe nce in Omega with radius across the tachocline at the equator. The results indicate variations of rotation close to the presumed site of the solar dyn amo, which may generate the ZZ-year cycles of magnetic activity.