Solar cycle changes in GONG p-mode frequencies, 1995-1998

We have analyzed 27 3 month sets of Global Oscillaiton Network Group (GONG) data from the end of cycle 22 and the beginning of cycle 23 and here prese nt evidence of significant shifts in the central frequencies and the even a -coefficients of the frequency splittings of the modes. The temporal behavi or of the even a-coefficients is better reproduced by the corresponding coe fficients of a Legendre polynomial decomposition of the surface magnetic he ld than by the total flux; i.e., the temporal variation is strongly correla ted with the latitudinal distribution of the surface magnetic activity. The se changes are consistent with available data from previous solar cycles. T he even a-coefficients, which sense the asphericity of the solar structure, appear to show similar temporal evolution at all depths. The odd a-coeffic ients, which sense the internal differential rotation, show no significant variation with time or depth. In particular they show no significant correl ation with either the magnetic flux or with the corresponding odd Legendre components of the flux. This suggests that the solar cycle related variatio n of the oscillation frequencies is not due to contamination of observed Do ppler shifts by the surface magnetic fields.