Over intra- and inter-annual time scales, the mean dynamic topography (MDT) variability in the Arctic Ocean largely results from changes in large-scale ocean circulation patterns both within the Arctic as well as from adjacent seas such as the North Atlan tic and the Nordic Seas [Forsberg et al., 2007]. Recent (ICESat) satellite-based observations reveal a ~2 mm/yr positive trend in MDT in the Beaufort sector of the Arctic Ocean during the last lustrum [Forsberg et al., manuscript in preparation]. While th e measured spatio-temporal pattern of MDT variation is generally consistent with predictions from various oceanographic models [e.g., Gao et al., 2005], significant differences can also be observed between observations and models as well as among models, which hampers and challenges validation. The retrieval accuracy of the MDT is also unclear.
A new era in MDT measurements over the Arctic Ocean is about to dawn with the upcoming launch of the GOCE and Cryosat missions from the European Space Agency (ESA ). GOCE was successfully launched in March 2009 and will improve the quantitative knowledge of the gravity field, and hence the geoid (Johannessen et al., 2003). CryoSat-2, which will determine sea-ice freeboard height and hence the sea ice thickness is s cheduled for launch in February 2010. The accuracy of Arctic MDT measurements depend critically on two key factors [Forsberg et al., 2007], the determination of the height of the sea ice freeboard above the sea surface, and the change in sea height associ ated with ocean tidal currents and motion. While the prospect of accurate sea-ice freeboard using sea-ice polynias and leads is very good, the second factor is in need of urgent improvement. The proposed research will target the latter by developing and d eploying geodetic-quality GPS sea-ice-drifting buoys to help improve the Arctic Ocean tidal and circulation models. The proposed research will moreover take advantage of applications and methods developed during the closing International Polar Year (IPY) and the new altimetry and gravity space missions to monitor Arctic climate change using improved MDT observations and models.