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Session 69 - The Solar Dynamo and Helioseismology.
Display session, Thursday, June 13
We measure the mean frequencies of acoustic waves propagating toward and away from sunspots employing a spot-centered Fourier-Hankel decomposition of p-mode amplitudes as measured from observations made at the South Pole in 1988 and 1991. There is a significant frequency shift between the inward and outward traveling waves which is consistent with the Doppler effect of a radial outflow from the sunspots. For p-modes of temporal frequencies of 3 mHz it is observed that the frequency shift decreases slightly with spatial frequency, for modes with degree \ell between 160 to 600. From the \ell dependence of the frequency shift, we infer that the mean radial outflow within the observed annular region (which extends between 30 and 137 Mm from the spots) increases nearly linearly with depth, reaching a magnitude of about 200 m/s at a depth of 20 Mm. This outflow exhibits properties similar to flows recently reported by Lindsey, et al. (1996 ApJ submitted) using spatially sensitive local helioseismic techniques.
This work is supported by NSF Grant AST 9496171 and NASA Grant NAGW-4143.
Program listing for Thursday