GRACE Water Storage Estimates in Finland and the Effect of Baltic Sea Level Variation

We compare the GRACE water storage estimates in Finland with the total water storage from a high-accuracy local hydrological model. Being a significant source of mass variations, we also discuss the leakage of the Baltic mass into estimates of continental water storage in GRACE solutions. For the total water storage, we use the model of the Watershed Simulation and Forecasting System (WSFS) of the Finnish Environment Institute. WSFS covers the whole hydrological cycle, including surface and subsurface water and snow. For GRACE water storage, we use three estimates obtained through different processing methods. First, we use the standard monthly GRACE gravity field solutions and apply appropriate filtering. To improve the spatial and temporal resolution, two regional solutions are studied. NASA has recently made available GRACE estimates of 10-days mass change in 4x4 degree blocks (mascons) over the worlds' continents covering the period April 2003 to April 2006. In addition to the mascon solutions, we will also use the regional solutions employing GRACE KBR data derived from in situ disturbance potential measurements via the energy conservation method. The monthly variation in the water mass of the semi-enclosed Baltic sea is about 60 Gt RMS. It is governed by the water exchange with the North sea through the Danish straits, and is difficult to catch in the global ocean circulation models. We study the contribution of Baltic mass variation to the GRACE estimates of water storage. On the other hand, the Baltic has both a dense network of tide gauges and several specific high-resolution hydrodynamical models, making it possibly the best-controlled mass variation of this size in the world. We discuss the possibilities of using Baltic mass to validate and compare GRACE solution methods.