Doppler radar radial wind assimilation using an hourly cycling 3D‐Var with a 1.5 km resolution version of the Met Office Unified Model for nowcasting

This article describes the development and trials at the Met Office of the assimilation of radar Doppler radial winds in a pre-operational framework. It uses a high-resolution 1.5 km convective-scale version of the Unified Model for nowcasting, on a small domain covering southern England and Wales. The assimilation was performed using a version of the Met Office 3D-variational data assimilation system at 1.5 km resolution. The Doppler radial wind observations were provided by the original four Dopplerized C-band single-polarization radars in the UK radar network, all situated in the south of England. This article provides a description of the Doppler radial wind observation operator, pre-processing, observation errors and data assimilation configuration. The system is tested on and verified for four case studies using continuous hourly cycling with 7 h forecasts. A significant positive impact for rain and wind is found in the first half of the forecasts (nowcasting time-scale).