Solar Cycle Variations of Subsurface Meridional Flows in the Sun

We study the subsurface meridional flow in the Sun as a function of latitude and depth in the period from 1994 to 2000, covering the solar minimum in 1996 and the maximum in 2000, with the technique of time-distance helioseismology. It is found that the velocity of meridional flow increased when solar activity decreased from 1994 to 1997. As solar activity increased from 1997 to 2000, a new component of meridional flow, centered at about 20° latitude, was created in each hemisphere. It moves away from its center. The new flow changes the observed meridional flow from poleward at solar minimum to equatorward at solar maximum at low latitudes. The velocity of the new component increases with depth at least down to a depth of 70,000 km.

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