Diagnosing the Droughts and Floods in Equatorial East Africa during Boreal Autumn 2005-08

Building on an earlier report on the 2005 drought in equatorial East Africa, this short note examines the circulation mechanisms of the anomalies in the boreal autumn short rains'' season in the subsequent three years. Westerlies during this season are the surface manifestation of a powerful zonal-vertical circulation cell along the Indian Ocean equator. The surface equatorial westerlies were fast during the 2005 and 2008 droughts, near average during the near-average 2007 short rains, and slack during the 2006 floods, consistent with the known circulation diagnostics.