The representation of the trade winds in ECMWF forecasts and reanalyses during EUREC⁴A

Abstract. The characterization of systematic forecast errors in lower-tropospheric winds is an essential component model improvement. This paper motivated by a global, long-standing surface bias the operational medium-range weather forecasts produced with Integrated Forecasting System (IFS) European Centre for Medium-Range Weather Forecasts (ECMWF). Over tropical oceans, excessive easterly flow found. A similar found western North Atlantic trades, where EUREC4A field campaign provides unprecedented wealth measurements. We analyze wind IFS and ERA5 reanalysis throughout entire lower troposphere during EUREC4A. varies greatly from day to day, resulting root mean square (RMSEs) up 2.5 m s−1, speed −1 s−1 near above trade inversion −0.5 reanalyses. These biases are insensitive assimilation sondes. modeled zonal meridional exhibit diurnal cycle that too strong, leading weak everywhere 5 km daytime but below 2 at nighttime strong. Removing momentum transport shallow convection reduces leads stronger cloud base. update moist physics newest (cycle 47r3) bias, especially daytime. Below 1 km, friction due unresolved physical processes appears be strong (partially) compensated dynamics, making this challenging coupled problem.