Solar Physics Division Meeting 2000, June 19-22
Session 1. Helioseismology, Magnetic Fields, Chromosphere and Transition Region
Display, Chair: C. U. Keller, Monday-Thursday, June 19, 2000, 8:00am-6:00pm, Forum Ballroom

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[1.07] A Wave-Theory Approach to Time-Distance Helioseismology

A. C. Birch (Department of Physics, Stanford University), A. G. Kosovichev (W.W. Hansen Experimental Physics Laboratory, Stanford University)

Time-distance helioseismology, which measures the time for acoustic waves to travel between points on the solar surface, has been used to study small-scale three-dimensional features in the sun, for example active regions, as well as large-scale features, for example meridional flow, that are not accessible by standard global helioseismology. The interpretation of travel times has typically been done in the ray approximation. The interaction of acoustic waves with features smaller than their wavelength, for example in active regions or in the tachocline, is not expected to be well represented by ray theory.

In order to develop a wave-based interpretation of time-distance data we employ the first Born approximation, which takes into account finite-wavelength effects and allows a single scattering between the source and receiver of the acoustic wave. We calculate the sensitivity functions, the solar equivalent of the 'banana-doughnut' kernels from terrestrial seismology, for the wave travel times and study the dependence of travel times on perturbations to a solar model. The wave travel times are compared with ray theory. This work was supported by NASA grant NAG-3077.

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