Development of a 11-year ERA* High Resolution Ocean Forcing Dataset

Abstract

In the framework of the European Space Agency (ESA) World Ocean Circulation project (WOC), the enhanced ocean wind forcing product (ERA*) has been developed to address the growing demand for accurate forcing from the ocean modelling community. The ERA* is a corrected reanalysis product that optimally combines the capacities of scatterometer observations and model reanalysis stress equivalent wind (U10S) output, by means of a geolocated scatterometer-based correction (SC) applied to the European Centre forMediumrange Weather Forecasts (ECMWF) Fifth reanalysis U10S output (ERA5). The SC consists of accumulated ERA5-scatterometer U10S component (zonal and meridional) differences over time windows of typically a few days to a month, at each ocean grid point (Trindade et al. (2020)). ERA* is able to introduce true smaller scale signal into ERA5 that corresponds to the physical processes absent or misrepresented by the latter, e.g., strong current effects (such as WBCs, highly stationary), wind effects associated with the ocean mesoscales (SST), coastal effects (land see breezes, katabatic winds), parameterization errors, and large-scale circulation effects, e.g., at the ITCZ. This is verified by comparing both products against independent scatterometer observations (e.g., HSCAT on HY-2A and HY-2B) and buoys winds. The ERA* product is generated for the period 2010-2020. An optimized configuration of ERA* in terms of the varying scatterometer constellation over the period of interest is sought. In particular, the optimal SC time window size will depend on the scatterometer sampling, i.e., the larger the number of scatterometers in orbit is, the smaller is the time window required. The ERA* reduces the vector root-mean-square difference by 10% (5%) against independent scatterometers (buoys), with respect to that of ERA5. The new ERA* product, which thus significantly outperforms ERA5, will be freely available from theWOC webpage (https://www.worldoceancirculation.org/)