Oceanic teleconnection and ocean-atmosphere coupling in the south-eastern Tropical Atlantic (HDR)

This dissertation retraces my scientific journey after completing my PhD at LEGOS (2005), which led me to work at JPL in California and later within IRD (since 2008) at LEGOS and several research laboratories of southern partners, including IMARPE and IGP in Peru, and UCT in South Africa. My research focuses on the study of oceanic dynamics and ocean-atmosphere interactions in the tropical Atlantic basin, complemented by inter-comparative studies of the Pacific basin. My research aims to better understand oceanic dynamics in the equatorial band (Pacific and Atlantic) across a wide range of frequencies (subseasonal to decadal) to improve our knowledge of this forcing, which propagates along the coasts of Angola/Namibia and Peru/Chile, modulating the variability in these two upwelling systems. This variability impacts marine ecosystems (habitats and the availability of fishery resources) and atmospheric circulation (regional climate and precipitation). My work demonstrates how these equatorial and coastal waves decompose into modes with specific characteristics (amplitude, speed), that control the timing of this equatorial connection and the maximum latitude at which it can be detected. I also evaluate the relative importance of remote forcing versus local forcing (coastal wind and heat fluxes) on coastal oceanic and biogeochemical variability. In addition, I conduct studies to better understand the phenology and drivers of extreme interannual events in the tropical Atlantic. My findings have shown that equatorial events, Atlantic Niños, and coastal events, Benguela Niños, are inextricably interconnected and exhibit complex dynamics involving nonlinear processes and interactions between oceanic and atmospheric connections at regional and basin scales. To address these issues, I use a methodology based on the inter-comparative analysis of observations combined with the use of simple and more complex models. I develop numerical approaches that include linear ocean models and community models (CROCO for the ocean, BioEBUS for biogeochemistry, and WRF for the atmosphere), deployed in regional contexts and adapted to the specific constraints of a region or a scientific question. My research perspectives aim to improve the predictability of extreme events in the equatorial Atlantic and in the upwelling systems of the Southern Hemisphere. This includes integrating coupled ocean-atmosphere models and artificial intelligence algorithms to produce more reliable forecasts. In parallel, my future work will explore coastal variability in the northern Gulf of Guinea, along the coasts of Cameroon, Togo, Benin, Ghana, Côte d’Ivoire, and Liberia, in connection with the remote equatorial variability and its impact on precipitation and the African monsoon. These studies aim to support sustainable management of marine ecosystems in the context of global climate change. A significant part of my activities is also dedicated to academic teaching in France and in the southern countries (Benin, South Africa, Vietnam). I actively contribute to capacity building in numerical modeling through training sessions (summer schools), supervision, and collaborations with countries in the South (Peru, Chile, Vietnam, South Africa, Benin, Côte d’Ivoire).