GRACE Applications to Ocean Circulation: a review of the first 5 years.

The nearly-5 year time series of subtle gravitational changes measured by GRACE, and its measurement of the time-averaged field, have provided new insights into the time-averaged and the time-varying oceanic circulation. Among these are interannual changes in the Arctic ocean and in the barotropic circulation of the Antarctic Circumpolar Current; when combined with radar altimetry, time changes in the heat content of the oceans become apparent, albeit at large spatial scales. The time-averaged geostrophic circulation is now much better constrained thanks to a unique combination of GRACE data, radar altimetry and surface float data. Assimilation of GRACE data into numerical models is now possible. Challenges also remain, especially at low latitudes, where the signals are weaker and the uncertainties larger. This presentation will provide a review of these results, a progress report in the application of GRACE data to ocean problems, and a set of challenges for future work.