Comparison of supergranular flows from doppler and local correlation tracking velocities

Details Comparison of supergranular flows from doppler and local correlation tracking velocities Comparison of supergranular flows from doppler and local correlation tracking velocities

May 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997spd....28.0259f&link_type=abstract

American Astronomical Society, SPD meeting #28, #02.59; Bulletin of the American Astronomical Society, Vol. 29, p.903

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Measurements of the flows in the solar photosphere rely upon two techniques: doppler measurements of the line-of-sight velocity or tracking of features or patterns moving perpendicular to the line-of-sight. These methods have differing characteristics. Doppler measurements can easily measure surface flows near the limb which are not seriously contaminated by p-modes or other solar sources. However, they require excellent instrument calibration over the full field of view. Even then vertical flows within supergranules are barely detectable. Correlation and feature tracking have proven useful for estimating transverse velocity using granules and other tracers. Nevertheless, they can be degraded by the intensity variations of p-modes and possibly other oscillatory motions, as well as by effects of limb darkening and foreshortening. The two methods would both be strengthened through detailed comparisons. Data collected by MDI/SOHO is ideal for this purpose. The data is co-spatial and co-temporal, and is all obtained through the same instrument. We compare Doppler velocities with those obtained through correlation tracking using high-resolution MDI/SOHO images. We focus on motions at positions exceeding 30 degrees from disk center. After taking projection effects into account, we combine the two measurements to form a three-dimensional picture of the flows in the average supergranule. This work was supported by NASA Grant NAG5-3077 at Stanford and Lockheed Martin, and by AFOSR and the Fellows Program of AF Phillips Lab at NSO/SP.

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