Strong winds in a coupled wave–atmosphere model during a North Atlantic storm event: evaluation against observations

Abstract

Strong winds may be biased in atmospheric models. Here the European Centre for Medium-range Weather Forecasts (ECMWF) coupled wave–atmosphere model is used (i) to evaluate strong winds against observations, and (ii) to test how alternative wind stress parametrizations could lead to a more accurate model. For the period of storms Kaat and Lilli (23–27 January 2014), we compared simulated winds with in situ – moored buoys and platforms – and satellite observations available from the North Atlantic. Five wind stress parametrizations were evaluated. The first result is that moderate simulated winds (5–20 m s−1) match with all observations. However, for strong winds (above 20 m s−1), mean differences appear, as much as −7 m s−1 at 30 m s−1. Significant differences also exist between observations, with buoys and Advanced Scatterometer ASCAT-KNMI generally showing lower wind speeds than the platforms and other remote-sensing data used in this study (AMSR2, ASCAT-RSS, WindSat, SMOS and JASON-2). Buoy and ASCAT-KNMI winds are likely to underestimate the real wind speed. It is difficult to conclude which dataset should be used as a reference. The second result is that common wave-age dependent parametrizations produce unrealistic drags and are not appropriate for coupling, whereas a newly empirically adjusted Charnock parametrization leads to higher winds compared to the default ECMWF parametrization. This proposed new parametrization may lead to more accurate results in an operational context.