34th Solar Physics Division Meeting, June 2003
Session 8 Helioseismology
Poster, Monday, June 16, 2003, 3:30-5:00pm, Mezzanine

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[8.08] Computational Seismic Holography of Active Region Subphotospheres

C. Lindsey, D. C. Braun (NorthWest Research Associates)

We apply phase-correlation seismic holography to SOHO/MDI observations of large sunspots to render signatures of local sound-speed anomalies in their shallow subphotospheres. In the computations reported here, a magnetic proxy we call the ``showerglass correction'' was applied to correct large phase errors introduced by surface magnetic fields. Preliminary results suggest a general sound speed enhancement in the range 1--4% up to depths of 10 Mm over horizontally extended regions surrounding large sunspots. These regions cover diameters roughly in the range 30--50 Mm. Phase maps of large active region complexes show signatures that tend to blanket most of the active region. The correlation between the phase shift and the magnetic field strength is generally high, but there are localized regions in which the phase signature departs significantly from the magnetic. The signature of the sunspot itself tends to be subtle with a maximum that may be significantly displaced towards the periphery of the active region. The research reported here is supported by funding from the Supporting Research and Technology and the Living with a Star Programs of the National Aeronautics and Space Administration, and from the Astronomical Sciences Division of the National Science Foundation.

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.