The operational 3DEnVar data assimilation scheme for the Météo-France convective scale model AROME-France

Abstract. Since October 2024 the Météo-France operational convective scale model AROME-France uses a 3DEnVar data assimilation (DA) scheme in order to improve the performances of severe weather prediction. This paper describes the configuration and the evaluation of this 3DEnVar scheme. It summarises the work carried out to configure this scheme in an operational context, with the inherent constraints of numerical robustness, compatible execution times and, of course, correct performances of the forecasts produced. The adjustment of horizontal and vertical localization, inflation, hybridization and the use of Incremental Analysis Update (IAU) are studied in sensitivity experiments, and the impact on the spin-up is investigated. A configuration, and its variation with IAU, are thus defined and evaluated using different scores over a long period and on different severe meteorological situations (winter storm, fog and High Precipitating Events): they largely outperform the operational 3D-Var. The version with IAU has been implemented in the new operational version of the AROME-France assimilation system.