Estimating ocean freshwater storage and ocean heat content from space gravimetry and satellite altimetry to constrain the Earth global water energy budget

Abstract:

Space gravimetry observations from GRACE and GRACE-FO enable to estimate the ocean freshwater storage since 2002. When satellite altimetry observations of sea level are corrected from the freshwater storage estimates derived from space gravimetry, they provide an estimate of the thermosteric sea level changes which are linearly related with the ocean heat content changes. The strengths of this satellite approach is to provide consistent vertically integrated ocean heat storage changes and ocean freshwater storage changes, with a quasi-global coverage and a high temporal resolution.

In this work we present recent advances which include the use of the latest GRACE and GRACE-FO realease, the use of the last terrestrial reference frame realization, a new water vapor correction on altimetry products that is consistent with the SSMI fundamental climate data record and refined estimates of the expansion efficiency of heat at global and regional scale. We propose new estimates of the ocean freshwater storage changes and ocean heat content changes with revisited uncertainties computations. We find the new uncertainties on the mean estimate over 2002-2019 are <0.35W.m^-2.

When these estimates are reintroduced a posteriori in the Earth global water energy budget thanks to a variational framework (similar to L’Ecuyer et al. 2015) we find that they tightly constrain the the top of the atmosphere radiation budget and the relationship between the global downward Long wave radiation at the surface, the upward longwave radiation and the upward shortwave radiation.