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D.A. Haber, B.W. Hindman, J. Toomre (JILA, Univ. of Colorado), R.S. Bogart, J. Schou (CSSA, Stanford Univ.), F. Hill (National Solar Obs.)
We report on the daily variations and average behavior of large-scale flows in the upper convection zone as determined by ring-diagram helioseismic analysis applied to SOI-MDI full-disk velocity data from the 1996 and 1998 Dynamics Campaigns. We have tracked many small regions of 15 degrees diameter whose centers are spaced 7.5 degrees apart in latitude and longitude, creating a mosaic of tiles that oversample the spatial domain. The tiles cover the solar disk out to a distance of 52.5 degrees from disk center. An individual dense-pack mosaic is prepared by tracking each of 189 regions for 1664 minutes (27.7 hrs). Successive mosaics are prepared every 15 degrees in Carrington longitude, roughly once every 1633 minutes. Such mosaics now cover more than two full Carrington rotations in 1996 and one rotation in 1998.
This is the best spatial and temporal coverage of any ring-diagram study carried out to date. The longitudinally averaged meridional flow varies with latitude but remains relatively constant with depth below the upper shear layer at 2 Mm down to a depth of about 16 Mm. The averaged zonal flow increases with depth within this same layer and agrees well with the rotation rates found from global modes. However with the high-degree wave field data from this analysis we are better able to resolve that shear layer within the upper convection zone. We see bands of faster averaged zonal flow near 30 degrees latitude both in the northern and southern hemisphere that are present at all depths studied. We also present movies of the daily variations in the flows within this dense pack for given depths that show the evolution of the complex velocity field.
This research was supported by NASA grants NAG5-3077 and NAG5-7996, and NSF grant AST-9417337.
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