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West African rainfall variability

Composite of African easterly waves (AEWs) from the National Center for Atmospheric Research (NCAR) Community Climate System Model (CCSM4) for the 1980-2005 period. AEWs are westward propagating, synoptic scale weather systems common to West Africa and the Atlantic during the boreal summer season. Shown In the diagram to the left are composite streamlines at 700mb (top), associated streamlines at 850mb (middle) and associated precipitation anomalies (bottom). Note the strong vorticity maximum at 850mb and positive precipitation anomalies within the wave trough. 

 

Christopher Skinner leads research focused on understanding the response of tropical dynamics, particularly the West African monsoon, to changes in radiative forcing.

The semi-arid Sahel region of West Africa experiences some of the most extreme variations in rainfall anywhere on Earth.  Persistent poverty, a lack of effective water management, and a dependence on rainfed agriculture make the populations of the Sahel particularly vulnerable to rainfall variability and climate change. Numerous local and remote mechanisms have been shown to control rainfall variability in West Africa, including the global distribution of sea surface temperatures, radiative forcing from aerosols and greenhouse gases, and land-atmosphere feedbacks.

A variety of numerical modeling techniques are used to gain new insights into how these mechanisms influence precipitation in West Africa and how changes in these processes will shape the response of West African climate to continued global warming. Large-scale and fine-scale processes are explored with the use of coupled atmosphere-ocean general circulation models, atmosphere only general circulation models, and nested high-resolution climate models. A particular emphasis is placed on evaluating the simulation of synoptic-scale African easterly waves and their interaction with convective processes over Africa. Results from this work offer insights into the physical mechanisms responsible for climate model biases and help to inform analysis of future climate projections.

Publications

  • Skinner, C.B.*, M. Ashfaq and N.S. Diffenbaugh, Influence of 21st century atmospheric and sea surface temperature forcing on West African climate, Journal of Climate, 25(2), 527-542, 2012.

  • Skinner, C.B.* and N.S. Diffenbaugh, The contribution of African easterly waves to monsoon precipitation in the CMIP3 ensemble, Journal of Geophysical Research – Atmospheres, 118, doi:10.1002/jgrd.50363, 2013.

  • Skinner, C.B. and N.S. Diffenbaugh, Projected changes in African easterly wave intensity and track in response to greenhouse forcing, PNAS, doi:10.1073/pnas.1319597111, 2014.