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J. Zhao, A. Kosovichev (W. W. Hansens Experimental Physics Laboratory, Stanford University)
Time-distance helioseismology has provided a unique tool for studying interior structures of the Sun. The structure of sound speed variations and flow fields beneath the sunspot surface have been obtained by the use of inversion techniques in some previous studies. By applying time-distance measurements and an inversion technique to active region NOAA 9114 observed by SOHO/MDI, which showed unusual fast rotation around its center during its passage on the solar disk, we obtained the sound-speed structure and plasma flow fields up to 10 megameters below the photosphere. The subsurface sound-speed structure revealed apparent structural twists relative to the surface magnetic structure, which may suggest that the magnetic twists have existed below the visible surface. For the flow fields, strong vortical flows can be seen near the surface and opposite vortex was found about 10 megameters below the surface, which may provide an explanation of magnetic twists in sunspots.
Same technique was applied to 86 active regions observed by SOHO/MDI in order to study the hemispherical preference of kinetic helicities of active regions. It was found that about 55% of active regions in northern hemisphere showed positive kinetic helicity, while 59% of southern hemisphere active regions showed negative kinetic helicity. This provides observational evidences to figure out where or how the observed surface magnetic helicity hemispherical preference forms.
The author(s) of this abstract have provided an email address for comments about the abstract: junwei@quake.stanford.edu
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.