Gravity tide and seasonal gravity variation at Ny-Ålesund, Svalbard in Arctic

We have analyzed 4 years of gravity data (September 1999–August 2003) obtained from the superconducting gravimeter at Ny-Ålesund, Svalbard in Arctic. The tidal analysis results indicate that the time variation in amplitude and phase of the short-period gravity tides may be due to the seasonal variation of the ocean tides, especially in the semidiurnal band. The gravity residuals, which were reduced from the following three effects from the original data: (1) the observed short- and long-period tides (up to the annual Sa wave) including the loading and attraction of ocean tide, (2) the air pressure and (3) the polar motion, show clear correlation with the computed hydrological effects (i.e. the effects of soil moisture and snow) in both the amplitude and phase. However, we found that the gravity data reveal a problem in the snow model at Ny-Ålesund that was used for the computation. The vertical motion obtained from the continuous GPS measurements carried out near the gravity station shows seasonal variations that are consistent with the gravity data at least in their sign.