Multi-decadal surface wind forcing products for the Copernicus Marine Service

Abstract

The ocean surface wind plays a key role in the exchange of heat, gases and momentum at the atmosphere-ocean interface. It is therefore crucial to accurately represent the wind forcing in physical ocean model simulations. A comparison of scatterometer observations and global numerical weather prediction (NWP) model wind fields revealed substantial local systematic errors in wind vector components and spatial derivatives. The widespread use of NWP model winds in the computation of ocean surface processes implies that these biases propagate into modelled air-sea fluxes, surface waves and currents. Temporally-averaged gridded differences between geolocated scatterometer wind data and NWP wind fields can be used to correct for persistent local NWP wind vector biases. By combining these scatterometer-based bias corrections with global, hourly NWP wind fields, high-resolution wind forcing products can be created for the ocean modelling community and other users. In 2022, new hourly and monthly Level-4 (L4) surface wind products were introduced in the Copernicus Marine Service catalogue. These products include global bias-corrected 10-m stress-equivalent wind, surface wind stress fields and spatial derivatives. The bias corrections are calculated from Copernicus Marine Service Level-3 wind products for a combination of scatterometers and their collocated European Centre for Medium-range Weather Forecasts (ECMWF) model winds. The hourly real-time product covers the past two years and uses ECMWF operational model forecasts. The hourly and monthly multi-year products currently span the period from August 1999 to 3 months before present-day and are based on the ECMWF ERA5 reanalysis. In 2024, the multi-year products will be extended backward to 1991, covering a period of more than 30 years. The spatial bias correction fields are found to be highly consistent between different scatterometers and over time. Compared to the uncorrected ECMWF winds, the L4 winds correspond better to moored buoy observations and independent scatterometer observations. Like any Copernicus Marine Service product, the wind products are freely and openly available for all operational, commercial and research applications.