Zonal wind variability and Sahel rainfall: 20th and 21st century

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Wednesday, 5 February 2014: 11:45 AM
Georgia Ballroom 1 (The Georgia World Congress Center )
David P. Whittleston, MIT, Cambridge, MA; and D. Entekhabi and A. Schlosser

We present work seeking to characterize zonal wind anomalies associated with interannual rainfall variability over the West African Sahel. As was found in CMIP3, CMIP5 modeling studies have failed to arrive at a consensus on 21st century rainfall projections in the region. This uncertainty is likely a product of parameterization schemes, whilst an incomplete understanding of what drives rainfall over the Sahel makes it challenging to diagnose particular model deficiencies.

By identifying relationships between rainfall and the variability of large-scale fields that are resolved in climate models (i.e. zonal wind), we hope to side step issues caused by rainfall parameterization. Furthermore, by considering the entire troposphere, our analysis captures the complex interaction between a number of phenomena linked to rainfall (the Tropical Easterly Jet, African Easterly Jet and monsoonal westerlies). Using robust modes of zonal wind variability, we then assess how these patterns are represented in the CMIP5 model runs. This allows us to investigate whether model deficiencies, or true disagreements in future forcing, explains the divergence of rainfall projections.