World Ocean Circulation : Algorithm Technical Baseline Document for ERAstar (v2.0)

Abstract

The ERA* stress-equivalent wind (U10S) and stress vector product is a correction of the ECMWF Fifth Reanalysis (ERA5) output by means of geo-located scatterometer-ERA5 differences over a few days temporal window. The version 2 products contain two different datasets: the nominal product over the period 2010-2020, which uses a temporal window of 15 days (except for 2010, in which a temporal window of 30 days is used); and an enhanced quality and resolution product for the years 2013, 2018 and 2020, which uses a temporal window of 3 days. Both products use, at any given time, all available scatterometer systems with global and continuous coverage. The enhanced product is only provided over those periods in which there is sufficient scatterometer sampling to allow the use of short temporal windows. The scatterometer-based corrections are computed from a combination of the following systems, i.e., the Advanced Scatterometers (ASCAT-A, -B, -C) onboard the EUMETSAT Metop satellite series, and the scatterometers onboard the ISRO Oceansat-2 (OSCAT) and SCATSat-1 (OSCAT2). ERA* can correct for local, persistent NWP model output errors associated with physical processes that are absent or misrepresented by the model, 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), PBL parameterization errors, and large-scale circulation effects, e.g., at the ITCZ