Assimilation of Ground‐Based Microwave Radiometer Temperature Observations Into a Convective‐Scale NWP Model for Fog Forecast Improvement

During the SOuthwest FOGs 3D (SOFOG3D) campaign, a unique network of eight ground‐based microwave radiometers (MWRs) has been deployed over the southwestern part of France in order to improve fog forecasting, among other objectives. Observations have been acquired from mid‐autumn to mid‐spring 2019/2020 with the aim of assessing the impact of the assimilation of such observations in the Application de la Recherche à l'Opérationnel à Méso‐Échelle (AROME‐France) numerical weather prediction model during fog conditions. For that purpose, temperature profiles derived from MWR measurements at six different locations have been assimilated for a time period of three months with a three‐dimensional variational assimilation system similar to the one used operationally in the AROME‐France numerical weather prediction model. Positive impacts on AROME‐France one‐hour background and analysis have been obtained, as well as statistically significant temperature improvements for up to eight hours of forecast during all weather conditions. Positive impacts are also demonstrated during fog conditions, both for a single case study and statistically for temperature and fog forecast scores over several fog events.