Projections of tropical cyclones and rainfall in the African Sahel could be improved with better understanding and representation of African easterly waves in models

  • 16 September 2015

African easterly waves (AEWs) propagate westward across the Atlantic Ocean, and are a key factor in the formation of tropical cyclones and Atlantic hurricanes (80% of major hurricanes in the Atlantic are linked to AEWs). They are also the dominant synoptic pattern affecting precipitation in Africa’s semi-arid Sahel region.

Accurately simulating AEWs is critical to predicting Atlantic tropical cyclones and hurricanes, but new research supported by the Climate Variability and Predictability program, and accepted for publication in the Journal of Climate, demonstrates several shortcomings in CMIP5 models preventing accurate representation of AEWs.

The authors, Elinor Martin and Chris Thorncroft, compared CMIP5 simulations to historical runs and atmosphere-only AMIP simulations to discover that the models fail to represent the strength of AEWs compared to observations--they are too strong and dry over Africa, and they do not propagate into the Atlantic with the same strength as observations indicate they should.

All models fail to properly represent the correlation between eddy kinetic energy and rainfall, and low resolution over the Guinea Highlands may contribute to the aforementioned problems representing the propagation of AEWs. As model resolution improves, additional investment in understanding AEWs could improve predictions of tropical cyclones.

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