Development of multiple cells in meridional flows and evolution of mean zonal flows from ring-diagram analyses

Meridional flows within the solar convection zone have been observed with both direct Doppler measurements and with local helioseismic techniques based on ring-diagram analyses and time-distance methods. Typically these mean Rows are poleward with speeds of roughly 20 m s(-1). Using ring-diagram analyses on a subset of the ms MDI Dynamics Program data, called the dense-pack data set, we find that a deviation from this general behavior occurs in 1999. A second meridional cell appears below the surface in the northern hemisphere. At the same time, the mean zonal flows do not reveal any evidence of this cell. The zonal bands or 'torsional oscillations' continue their steady migration toward the equator.