Authors: I. Gonzalez-Hernandez, R. Komm, T. Corbard, F. Hill, R. Howe
Affiliation: National Solar Observatory, Tucson, Arizona
Ring Diagram analysis, a local helioseismology technique, has proven very useful
in order to study the solar subsurface velocity flows up to a depth of about
0.97Rsun. The depth range is determined by the modes recovered in this type
of analysis and thus depends on the size of the analyzed area. Extending the
working area allows to detect lower l modes that penetrate deeper in the Sun.
However, there is a compromise between the size of the patch and the validity
of the plane wave approximation used by the technique.
In this work we present a preliminary attempt to go deeper under the solar surface
using Ring Diagrams. To this end, we have studied patches of 30 degrees diameter
over the solar surface as they crossed the solar central meridian. These patches
are twice the size of the typically studied sections of 15 degrees in diameter.
A set of 15 overlapping sections centered at latitudes 0 ±7.5,+/-15,+/-22.5,+/-30.0,+/-37.5,+/-45.0
and ±52.5 have been analyzed for 25 intervals of 1664 minutes during
Carrington rotation 1989. We compare the differential rotation obtained by averaging
the zonal component of the horizontal velocity vectors with the global one to
test the validity of the technique. We finally derive the meridional circulation
from both GONG network and MDI dynamics program data. The depth dependence of
the meridional flow is of great importance for the understanding of the solar
dynamo which is one of the goals for HMI.