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Session 2 - Everything Else.
Display session, Friday, June 27
Ballroom C, Chair: Richard Canfield

[2.01] Persistence of Large-Scale Flows Beneath Quiet Sun: Local-Area Analysis Using MDI Doppler Data

D. Haber, J. Toomre (JILA, University of Colorado), R. Bogart, J. Schou (CSSA, Stanford), I. Gonzalez (IAC), F. Hill (NSO, NOAO)

Knowing the large-scale flows that occur in the upper convection zone is critical to our understanding of the processes that govern the solar cycle. Here we apply solar oscillation ring-diagram analysis to several small tracked regions on the sun, approximately 15^\circ on a side, as they rotate across the solar disk, in order to determine the persistence and depth variation of the large-scale flows beneath these regions. We use the Doppler velocity images from the Michelson Doppler Imager (MDI) instrument aboard the Solar Heliospheric Observatory (SOHO) satellite using quiet-sun data taken during the MDI Dynamics campaign of 1996. Three regions at different latitudes were extracted from full-disk Doppler images of 1024 \times 1024 pixels (pixel size \sim 2'' square) with a one-minute temporal cadence. Eight sequential 1536-minute time intervals were tracked, remapped onto great-circle grids, spatially and temporally filtered, and apodized in space and time. They were then Fourier transformed in two spatial dimensions and time. The resulting power spectra show characteristic rings at each frequency slice. Shifts in the center positions of the rings are caused by underlying flow fields and can be inverted to map these flows with depth. We use several techniques to fit these shifts in order to assess the stability of the results.


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