The SWAG Project

The SWAG project aims at a better understanding of the impact of the surface-atmosphere coupling on atmospheric disturbances and their consequences, including extreme events, in the tropical Atlantic. We are particularly interested in the role of the coupling in West Africa and the surrounding Eastern Atlantic Tropical Ocean regions, which are key regions of the global climate, in particular concerning tropical cyclogenesis.

It is a part of the world where the meteorological weather forecasts and the predictions of climate models are the most uncertain. The existence of large discrepancies in the representation of the West African Monsoon (WAM) system in these models is still an open issue, owing to the complexity of the land-sea-atmosphere interactions. Moreover, tropical disturbances travelling westward across West Africa in the late summer contribute significantly to the Atlantic hurricane season. Hence, the region of interest is also a key region for tropical cyclogenesis affecting both the USA and the Caribbean (e.g. Hurricane Irma, 2017).

The SWAG project concerns the interface between meteorology, oceanography, chemistry and physical and mathematical modeling. It is based on the implementation of a coupled mesoscale modeling tool including the oceanic model NEMO and the atmospheric model WRF-Chem, as well as the analysis of satellite observations, data from field campaigns and idealized simulations. The project involves three complementary aspects, with increasing degrees of complexity in terms of land-sea-atmosphere-aerosol coupling.

The SWAG project investigates the impact of ocean-atmosphere coupling on atmospheric disturbances within the WAM system. These disturbances are related to the mesoscale cyclonic vortices in the lee of large organized Mesoscale Convective Systems (MCSs), which can yield tropical cyclones, and are modulated by the moist monsoonal inflow at low-levels, the African Easterly Jet (AEJ) and the so-called African Easterly Waves (AEWs).

An other key issue is the impact of Saharan dust on the dynamical components of the WAM, and in turn, on tropical cyclogenesis.

Our last objective is to investigate the impact of the atmospheric and oceanic environment on the transition of mesoscale cyclonic vortices to tropical storms and cyclones, and on the intensification of the resulting tropical cyclones. The intensification of tropical cyclones indeed remains one of the most challenging issues in their prediction. The competition between processes pertaining to atmospheric dynamics and composition as well as air-sea interactions will be explored to segregate conditions favorable from those detrimental to the intensification of tropical disturbances. The impact of Saharan dust and upwelling systems (in the Gulf of Guinea and offshore Senegal) on the storm-to-cyclone transition will be thoroughly analyzed, together with the feedback mechanisms between dust aerosols, surface winds and air-sea interactions over the tropical Atlantic.