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

Since October 2024 the Météo-France operational convective scale model AROME-France has been using a 3DEnVar data assimilation (DA) scheme in order to improve the performance of severe weather prediction. This paper describes the configuration and evaluation of this 3DEnVar scheme. It summarizes 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 performance of the forecasts produced. The adjustment of horizontal and vertical localization, inflation, hybridization, and the use of Incremental Analysis Updates (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 storms, fog, and High Precipitating Events): they largely outperform the operational 3D-Var. The version with IAU was implemented in the new operational version of the AROME-France assimilation system.