The resolving power of current helioseismic inversions for the sun's internal rotation

Abstract

The inferred internal solar rotation rate obtained from helioseismic inversion is a nonlocal average of the true rotation rate; hence some care is required in the interpretation of the results of such inversions. We present kernels which describe the weighting of the average, for an inversion that is representative of recent work. Of particular interest is the fact that the so-called polar rate is actually an extrapolation from lower latitudes: the current helioseismic data do not permit us to construct a solution whose averaging kernel is localized at high solar latitude. Nonetheless, our results do not change the basic conclusion that the average radial gradient of the rotation rate in the solar convection zone is small. Finally, we demonstrate that more localized measures of the solar rotation are possible with the more complete data that should become available from new helioseismology projects. Subject headings: Sun: interior-Sun: oscillations-Sun: rotation 1. INTRODUCTION Measurements of the frequencies of normal modes of oscillation of the Sun lead to inferences about the structure and dynamics of the solar interior. In particular, the differences in the frequencies of modes of different azimuthal orders m (known as frequency splittings) have been used to obtain helio-seismic determinations of the rotation rate as a function of latitude at fractional radii 0.5 < 0.85, where r is the radial coordinate and R is the photospheric radius (Brown et al.