Physics
Scientific paper
May 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agusmsp11c..04w&link_type=abstract
American Geophysical Union, Spring Meeting 2005, abstract #SP11C-04
Physics
7522 Helioseismology
Scientific paper
Helioseismic inversions for subsurface supergranular motion have been performed using spectral-domain covariance estimates of the surface wave field as input data. The surface wave measurements used in this study were obtained from a 34-hr sequence of SOHO/MDI high-resolution Doppler images covering an approximately 210 Mm x 210 Mm corotating patch of the photosphere near disk center. The utilized signal, derived by filtering the Doppler sequence, is dominated by p- and f-modes in the frequency range 2.5 - 5.5 mHz and the range 600 - 1800 of angular degree. The helioseismic forward model used for the inversions is based on a wave equation which includes a stochastic driving term and a damping term. The effect of subsurface flows on wave propagation is treated in the single-scattering Born approximation. Several approaches to inverting helioseismic covariance data were used, including the method of optimally-localized averages. The inversions provide evidence for supergranular-scale motion to a detection depth of 6 Mm beneath the photosphere. The measured correlation coefficient between the surface motion and the motion at depth is observed to decrease with depth, but, contrary to some previous findings, does not change sign over the detectable depth range. The author is indebted to Yuhong Fan and Aaron Birch for extensive discussions about the theoretical aspects of wave propagation in flows and to the former for vital solar model outputs. The study was supported by NSF grant ATM-0223127.
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