Solar-cycle variation of the sound-speed asphericity from GONG and MDI data 1995-2000
Howe, R.; Hill, F.; Schou, J.; Antia, H. M.; Basu, S.; Komm, R. W.
India, United States
Abstract
We study the variation of the frequency splitting coefficients describing the solar asphericity in both GONG and MDI data, and use these data to investigate temporal sound-speed variations as a function of both depth and latitude during the period 1995-2000 and a little beyond. The temporal variations in even splitting coefficients are found to be correlated to the corresponding component of magnetic flux at the solar surface. We confirm that the sound-speed variations associated with the surface magnetic field are superficial. Temporally averaged results show a significant excess in sound speed around r=0.92Rsolar and latitude of 60°.