Saharan - West African Monsoon Multi-scale Analysis (SWAMMA)

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The West African Monsoon is critical to the livelihoods of millions, but remains a major challenge for weather and climate prediction. The monsoon provides moisture for large systems of thunderstorms that provide the annual rainfall in the Sahel. The monsoon is driven by the summertime heating over the continent. The Sahara exhibits the highest summertime temperatures and it is known that the monsoon is sensitive to the heating in the Sahara and the Sahel. The heating in the Sahara is controlled by dust, cloud and ventilation by colder air from the Sahara's margins. It is known that models exhibit major differences in this region, which is for example important for monsoon onset, but historically there has been an absence of data with which to evaluate models. Recent research has shown that the monsoon, dust and the storm-systems form a fully coupled system and that global models exhibit major biases in the couplings within this system. Operational models fail to capture the organisation, location and timing of the monsoon rains and this leads to incorrect coupling between the storm systems and the monsoon. Operational models also fail to represent the haboob dust storms generated by the storm systems, which are likely the main driver of dust emission in the summer. This means that even operational models which include dust fail to accurately capture the impacts of the dust on the meteorology, since a major dust emission mechanism is missing in the models. Recent research has also shown the existence of larger dust particles over the Sahara than previously observed, which will affect heating rates, feeding back on to the meteorology. SWAMMA will bring together a recently-developed model that can for the first time capture these couplings with recently-acquired data from this highly data-sparse region (collected during the NERC-funded AMMA and Fennec projects). SWAMMA will therefore combine for the first time a model that should be able to represent the key features of the summertime energy budget of the monsoon system with the first data sufficient to evaluate such a model. SWAMMA will evaluate the new model, quantifying the winds that generate dust uplift in the Sahara and Sahel. It will use the new data to analyse the impacts of variations in the sizes of dust particles. SWAMMA will evaluate the energy budgets of the monsoon system using both models and observations from AMMA and Fennec. SWAMMA will quantify how the coupled processes of the monsoon system respond to the seasonal evolution of the monsoon's boundary conditions to control the seasonal stability of the monsoon rainfall and its variability. By bringing together the recently-acquired data and the new model with existing weather and climate models the project will evaluate how process errors in operational models lead to systematic errors in predictions, both over West Africa and globally. The project will provide metrics for the processes that must be captured by operational models for them to capture the key processes and couplings in the West African monsoon system.