1. Meridional Circulation Variability from Large-Aperture Ring Diagrams Irene González Hernández Rudi Komm Thierry Corbard Frank Hill Rachel Howe Deborah Haber

2.  Introduction  Local Helioseismology. Ring Diagrams Technique  Large-Aperture Ring Diagrams  Meridional Circulation variability  Conclusions

3. Meridional Circulation and Dynamo Models  Dikpati, Mausumi; Gilman, Peter A. "Flux-Transport Dynamos with α-Effect from Global Instability of Tachocline Differential Rotation: A Solution for Magnetic Parity Selection in the Sun". ApJ, 559, 428  Gilman, P.A and Miesch, M. "Limits of Meridional Circulation Below the Solar Convection Zone" ApJ, 611, 568.  Haber, Deborah A.; Hindman, Bradley W.; Toomre, Juri; Bogart, Richard S.; Larsen, Rasmus M.; Hill, Frank. "Evolving Submerged Meridional Circulation Cells within the Upper Convection Zone Revealed by Ring-Diagram Analysis". ApJ,570, 855  McDonald, E.; Dikpati, M. "Evolution of Large-scale Solar Magnetic Fields in the Presence of a Multi-cell Meridional Flow". American Astronomical Society Meeting 204, #53.06 Courtesy of E. McDonald

4. Ring Diagrams technique 1664 min 16 o

5. Ring Diagrams technique

6. Synoptic Maps from Ring Diagrams

7. Large-Aperture Ring Diagrams

8. Rotation rate from Ring Diagrams 15° patches30° patches

9. Meridional Circulation Variability

10. Meridional Circulation Countercell

11. Meridional Circulation Variability

13. Conclusions / Future work  Large-aperture ring diagrams are effective in order to search for differential rotation and meridional circulation in deeper layers under the solar surface.  The presence of the countercell/down flow and the systematic differences in the averaged horizontal flows between GONG and MDI are still under investigation.  The results obtained from analyzing 25 Carrington rotations show a slight increase in the magnitude of the meridional flows with depth; however, the major increase below 0.965 Ro is suspected to be an artifact of the inversions.  There is a limit to the depth that can be reached using the standard Ring Diagram analysis due to the plane wave approximation used by the technique.  Our intention is to use GONG continuous velocity data to search for a meridional circulation variation with the solar cycle.