Solar convection-zone dynamics, 1995-2004

The nine-year span of medium-degree helioseismic data from the Global Oscillation Network Group ( GONG) and the Michelson Doppler Imager (MDI) allows us to study the evolving zonal flows in the solar convection zone over the rising phase, maximum, and early declining phase of solar cycle 23. Using two independent two-dimensional rotation inversion techniques, we investigate the depth profile of the flow pattern known as the torsional oscillation. The observations suggest that the flows penetrate deep within the convection zone - perhaps to its base - even at low latitudes, and that the phase of the pattern is approximately constant along lines of constant rotation rather than lines of constant latitude.