The gravitational field through the seasons

These variations have been factored into the latest “Potsdam gravity potato,” which GFZ experts have computed using data from the GOCE, GRACE and LAGEOS satellites. For this purpose, the Potsdam-based researchers created a new gravitational field model that takes into account the hydrologic balance of the continents as well as the melting and expanding ice masses in the polar regions. Called EIGEN-6C, this model is even more accurate than previous gravitational field models and was developed in close collaboration with researchers from Toulouse. Dr. Christoph Förste and Dr. Frank Flechtner, who chair the gravitational field working group at the GFZ, emphasise particularly the importance of ESA’s GOCE satellite for supplying measurements of the mean static gravitational field of the oceans. These measurements are essential to estimating the mean dynamic topography of the oceans, which facilitates a more accurate determination of the ocean currents. In addition to GOCE, long-term gravity measurement data have been supplied by the NASA-DLR twin satellite mission GRACE. GRACE has made it possible for the first time to record the large-scale temporal variations in the gravitational field that are caused by mass redistributions on the Earth’s surface. These redistributions include glacier melting in the polar regions as well as seasonal water storage fluctuations in large river basins. Due to these improvements, the new Potsdam potato is no longer a static body, but, for the first time, a surface that changes with time and provides information on climate-relevant processes in the Earth system. The GRACE mission will end in 2015 but a follow-up mission is planned for August 2017. “By then more than two decades of data will enable us to learn a great deal about the long-term, large-scale changes of the Earth that we might otherwise not have detected by other methods,” says Förste.

Andreas Fischer