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Session 2 - Everything Else.
Display session, Friday, June 27
Ballroom C, Chair: Richard Canfield
We have computed photospheric velocity flow maps from simultaneous observations taken with MDI and at the Swedish Vacuum Solar Tower (SVST) on La Palma on August 15, 1996. Both sets consist of a series of photospheric images, and flow maps are computed by following the local motions of granules. The MDI data have the important advantages of very stable images and longer continuous coverage of the same area of the solar surface. This longer coverage is necessary to study the evolution of mesogranules, supergranules, and to detect possible low amplitude motions on scales larger than supergranules. However, the high resolution mode of MDI is limited by the small telescope size to about 1.2 arc seconds angular resolution and uses a 0.6 arc second pixel size. This is adequate to show granulation but has the rms constrast significantly reduced to about 2%. Early efforts adapting techniques that were successful with higher resolution ground based images gave poor results and although new methods have now been developed, there are still some problems with accuracy. On the other hand, the SVST images have much higher angular resolution (as good as 0.2 arc second) but suffer from variable atmospheric distortion. They also have a much smaller field of view. By detailed comparison of the two data sets and by using CT and FT techniques to track the motions, we hope to understand the sources of any differences between them and to develop credible correction parameters to the MDI data sets if necessary.
This work was supported by NASA Grant NAG5-3077 at Stanford and Lockheed Martin, by AFOSR and the Fellows Program of AF Phillips Lab at NSO/SP, and by the Swedish Royal Academy of Sciences.
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