Sensitivity of Acoustic Wave Travel Times to Sound‐Speed Perturbations in the Solar Interior

Abstract

For time-distance helioseismology, it is important to establish therelationship between the travel times of acoustic waves propagatingbetween different points on the solar surface through the solar interiorand local perturbations to the sound speed in the propagation region.We use the Born approximation to derive a general expression forthe linear sensitivity of travel times to local sound-speed perturbationsin plane-parallel solar models with stochastic wave sources. Theresults show that the sensitivity of time-distance measurements toperturbations in sound speed depends on the details of the measurementprocedure, such as the phase-speed filter used in typical time-distancedata analysis. As a result, the details of the measurement procedureshould be taken into account in the inversion of time-distance data.Otherwise, the inferred depths of perturbations may be incorrect.