The AROBASE project aims to assemble a kilometre-scale limited-area multi-coupled modelling system of the physico-chemical atmosphere, the ocean (including sea-ice and marine biogeochemistry), waves and land surfaces (soil, vegetation, cities, snow, lakes and rivers) with important development criteria that are i) the transportable nature of the regional multi-coupled model and ii) the modular aspect to couple the relevant environmental components according to different applications. The AROBASE platform that will combine the AROME atmospheric model (with online chemistry and interactive aerosols) with the external surface model SURFEX, CTRIP for hydrological routing, NEMO and MFWAM for ocean and waves respectively, is built in the line of a seamless continuum of coupled modelling systems developed and used at CNRM, LACY and Météo-France. AROBASE will first help to improve the understanding and representation of the exchange processes between the compartments of the meteorological and environmental system at fine scale. It is also a new tool for high-resolution numerical weather prediction, which makes it particularly necessary to guarantee its performance in the forecast mode and its relevance for monitoring and anticipating meteorological phenomena and their consequences. AROBASE is finally an important step to prepare the new generation of the regional climate model (CNRM-RCSM) towards a kilometre resolution with new integrated components. The first results of the AROBASE platform will be presented during the conference, with a focus on the ocean-atmosphere-wave coupling, the air-sea interactions implied during severe meteorological situations over France metropolitan area and over-seas domains and impacts on numerical weather prediction.

The performance in term of tropical cyclone track and intensity prediction of the new coupled oceanatmosphere system based on the operational atmospheric model AROME-Indian Ocean and the ocean model NEMO is assessed against that of the current operational configuration in the case of seven recent tropical cyclones. Five different configurations of the forecast system are evaluated: two with the coupled system, two with an ocean mixed layer parameterization and one with a constant sea surface temperature. For each ocean-atmosphere coupling option, one is initialized directly with the MERCATOR-Ocean PSY4 product as in the current operational configuration and the other with the ocean state that is cycled in the AROME-NEMO coupled suite since a few days before the cyclone intensification. The results show that the coupling with NEMO generally improves the intensity of cyclones in AROME-IO, reducing the mean intensity bias of the 72 h forecast of about 10 hPa. However, the impact is especially significant when the TCs encounter a slow propagation phase. For short-term forecasts (less than 36 hours), the presence of a cooling in the initial state that has been triggered by the AROME high-resolution cyclonic winds in a previous coupled forecast already improves the tropical cyclone intensity bias of 2-3 hPa for both coupled or uncoupled configurations.

The performance in term of tropical cyclone track and intensity prediction of the new coupled oceanatmosphere system based on the operational atmospheric model AROME-Indian Ocean and the ocean model NEMO is assessed against that of the current operational configuration in the case of seven recent tropical cyclones. Five different configurations of the forecast system are evaluated: two with the coupled system, two with an ocean mixed layer parameterization and one with a constant sea surface temperature. For each ocean-atmosphere coupling option, one is initialized directly with the MERCATOR-Ocean PSY4 product as in the current operational configuration and the other with the ocean state that is cycled in the AROME-NEMO coupled suite since a few days before the cyclone intensification. The results show that the coupling with NEMO generally improves the intensity of cyclones in AROME-IO, reducing the mean intensity bias of the 72 h forecast of about 10 hPa. However, the impact is especially significant when the TCs encounter a slow propagation phase. For short-term forecasts (less than 36 hours), the presence of a cooling in the initial state that has been triggered by the AROME high-resolution cyclonic winds in a previous coupled forecast already improves the tropical cyclone intensity bias of 2-3 hPa for both coupled or uncoupled configurations.