Solar-cycle variation of the sound-speed asphericity from GONG and MDI data 1995-2000

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 soundspeed variations associated with the surface magnetic field are superficial.Temporally averaged results show a significant excess in sound speed around r ¼ 0:92 R ( and latitude of 608.