Inversions for average supergranular flows using finite-frequency kernels

Abstract

I analyze the maps recording the travel-time shifts caused by averaged plasma anomalies under an "average supergranule," constructed by means of statistical averaging over 5582 individual supergranules with large divergence signals detected in two months of Helioseismic and Magnetic Imager Dopplergrams. By utilizing a three-dimensional validated time-distance inversion code, I measure a peak vertical velocity of 117 ± 2ms-1 at depths around 1.2 Mm in the center of the supergranule and a root-mean-square vertical velocity of 21ms-1 over the area of the supergranule. A discrepancy between this measurement and the measured surface vertical velocity (a few ms-1) can be explained by the existence of the large-amplitude vertical flow under the surface of supergranules with large divergence signals, recently suggested by Duvall & Hanasoge. © 2012. The American Astronomical Society. All rights reserved.