  Ring diagram analysis of solar oscillation power spectra obtained from MDI
data is performed to study the velocity fields within the solar convection
zone. The three dimensional power spectra are fitted to a model with a
Lorentzian profile in frequency and includes the advection of the wave front by
horizontal flows to obtain the two horizontal components of flows as a function
of the horizontal wave number and radial order of the oscillation modes. This
information is then inverted using the OLA and RLS techniques to infer the
variation in flow velocity with depth. The resulting velocity fields yield the
mean rotation velocity at different latitudes which agrees reasonably with
helioseismic estimates. The zonal flow inferred in the outermost layers also
appears to be in agreement with other measurements. A meridional flow from
equator polewards is found to have an amplitude of about 25 m/s near the
surface and the amplitude appears to increase with depth.

Astrophysics