Sea Surface Temperature-Forced Monsoon Evolution and Variability in West Africa

DESCRIPTION: The West African monsoon delivers most of the annual rainfall to the Sahel region in a short but intense rainy season. Since agriculture remains the dominant economic activity in terms of percent of population engaged, understanding and predicting the variability in both the magnitude and timing of the monsoon season is especially important and potentially devastating if not prepared for. This work;will directly contribute to improving seasonal to interannual prediction of monsoon rainfall. The results of this work will be highly relevant to climate prediction organizations interested in helping the Sahel such as the International Research Institute for Climate and Society and its long-standing partners in West Africa. Through various channels, information from the study can inform applications;of climate information for better decision-making in the Sahel. The work will also support a graduate student. Knowledge gathered from this study will also contribute to the teaching of climate and society in the School for International and Public Affairs (SIPA) at Columbia University programs. The goal of this project is to improve the understanding and prediction of the West African summer monsoon, specifically response to changes in sea surface temperatures in the surrounding tropical oceans. Information on sea surface temperature fluctuations is routinely available and is important for climate prediction. The seasonal amount of Sahel monsoon rains, varies from year to year sometimes dropping to drought levels with serious effects on society. This variability has been linked to sea surface temperature fluctuations in remote and nearby ocean areas. Past studies have shown a that summer monsoon rains tend to weaken and sometimes fail when eastern tropical Pacific sea surface temperatures are relatively warm, a state known as the El Niño. Rains tend to be strong and plentiful when the east tropical pacific are relatively cool, during the La Nina phase. However, this association is not steady because the region is also sensitive to temperature changes in other basins, such as the tropical Atlantic and the Indian Oceans. Utilizing an atmospheric global climate model, in which different sea surface temperature scenarios are prescribed in the global ocean mimicking what is found in observations, this research will elucidate how the monsoon responds to changes in local and remote sea surface temperature changes in different basins, acting separately and together. By understanding the response pattern and the mechanisms of momentum, heat and moisture transport as a function of time, it is anticipated that possibilities of prediction of monsoon rainfall, based on pre-season sea surface temperatures conditions, will be advanced. This experimental method also provides a measure of "signal-to-noise" ratio in the monsoon rainfall. Putting the observations in that perspective will help frame better the prediction uncertainties, also helping advance the quality of monsoon season prediction.

OUTCOMES: This study supported graduate student, C. Pomposi, who defended her PhD dissertation and is currently a postdoctoral research scientist under the NOAA [Post-docs Applying Climate Expertise] PACE program. She is also leading the project team in revising a paper addressing the motivation for this study, including early modeling results.

IRI Data Library technology-based "Maprooms" that explore the influence of sea surface temperatures on the subseasonal character or precipitation across West Africa, based on data that merges local meteorological records and satellite observations:

http://cradata.agrhymet.ne/maproom/Climatology/Climate_Forecast/NARI_Prob_Precip.html

http://cradata.agrhymet.ne/maproom/Climatology/Climate_Forecast/SSTi_Prob_Precip.html