Evolving Large-Scale Flows With Advancing Solar Cycle Using Helioseismic Dense-Pack Ring-Diagram Analyses

Details Evolving Large-Scale Flows With Advancing Solar Cycle Using Helioseismic Dense-Pack Ring-Diagram Analyses Evolving Large-Scale Flows With Advancing Solar Cycle Using Helioseismic Dense-Pack Ring-Diagram Analyses

May 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sp22a02h&link_type=abstract

American Geophysical Union, Spring Meeting 2001, abstract #SP22A-02 INVITED

Physics

7522 Helioseismology, 7536 Solar Activity Cycle (2162)

Scientific paper

We have recently completed the first local helioseismic ring-diagram analysis of the entire SOI-MDI Dynamics Program data. These data sets include up to three months of continuous Doppler velocity data from each of the years 1996 through 2000. A single ring-diagram analysis over a 15o region of the sun, followed by an inversion of the frequency shifts thus obtained, yields measurements of the horizontal velocity field as a function of depth within the upper 14 Mm of the convection zone beneath that region. By performing the analysis over a Dense-Pack mosaic of 189 overlapping tiles and repeating the procedure for each day of data, we have mapped the velocity field as a function of time over a substantial fraction of the solar disk for a number of full Carrington rotations. Our studies of the dynamics of the upper convection zone have revealed the presence of striking north-south asymmetries in both the zonal and meridional flows as a function of depth. For example, a small second meridional flow cell appeared at depths below 10 Mm at latitudes north of 45oN in 1998, expanded upwards to 3 Mm in depth at all latitudes above 22oN in 1999, and then receded again in 2000. Synoptic maps, formed from nearly 4500 ring-diagram analyses per Carrington rotation, show that active regions are sites of convergent flow and appear at the boundaries of the northern meridional cells in 1999. Even finer sampling grids show that there are steep gradients in the flows within active regions. Our work has also revealed a relationship between the fast zonal "torsional oscillation" bands that migrate towards the equator and the meridional flow as the solar cycle progresses. The dominantly poleward meridional flow reaches maxima in both hemispheres at the latitudes at which the zonal fast belts occur. As the zonal fast belts drift towards the equator, the latitudes of maximal meridional flow also drift equatorward.

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