Modelling the differential impact of 1984 and 1950 sea-surface temperatures on sahel rainfall

✍ Scribed by Leonard M. Druyan; Stefan Hastenrath

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 1003 KB
• Volume: 11
• Category: Article
• ISSN: 0899-8418
• DOI: 10.1002/joc.3370110403

✦ Synopsis

Abstract

Experiments with the GISS general circulation model are analysed to evaluate the differential impact of the contrastingly different 1984 and 1950 sea‐surface temperature (SST) patterns on simulated precipitation over sub‐Saharan Africa. Simulations yielded significantly lower August rainfall with 1984 SST as compared with 1950 SST. Differences in the moisture convergence into the Sahel responsible for the different resultant precipitation conditions are related to different evolutions of key circulation features. These are, in turn, consistent with some 1984 vs. 1950 SST differences in the Atlantic Ocean. In the model scenario, anomalously warm surface waters in July 1984 deepened the near‐equatorial trough over the coastal waters adjacent to north‐west Africa, promoting a circulation that eventually inhibited moisture advection from the Gulf of Guinea to the Sahel. This atmospheric evolution included a southward expansion of the West African Mid‐tropospheric jet, which has been observed to occur during dry summers. The study suggests that this structure is a symptom of drought rather than a cause.