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).