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Session 69 - The Solar Dynamo and Helioseismology.
Display session, Thursday, June 13
The extended observation of the solar surface with frequent sampling provided by MDI on SoHO offers the chance to observe the evolution of supergranules and to measure surface flows associated with active regions and perhaps larger scale zonal and meridonal flows. We have used local correlation tracking of the granulation pattern for measuring surface flows from MDI high resolution continuum images. The datasets consist of 1024 x 1024 pixel images collected with a cadence of one minute and extending many hours each. The images are typically centered upon the central meridian of the sun and offset to the north of sun center, spanning roughly 40 degrees of solar longitude and from approximately -10 to +30 degrees of solar latitude. The latitude dependence of the differential rotation is evident. We present preliminary results of our search for signatures of mesogranules, supergranules and giant cells. On 23 Feb. 1996, we obtained a 12-hour continuous sequence including quiet sun near disk center and NOAA region 7946 at about N08 E30. The active region grew rapidly over this interval, forming several sunpots. We show preliminary comparisons of the measured flow fields with coaligned SOI/MDI magnetograms taken at 15-minute intervals.
The SOI/MDI program is supported by NASA grant NAG5-3077.
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