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

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  • 1 Department of Atmospheric and Oceanic Sciences, University of Wisconsin—Madison, Madison, Wisconsin
  • | 2 Kenya Meteorological Department, Nairobi, Kenya
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Abstract

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.

Corresponding author address: Stefan Hastenrath, Department of Atmospheric and Oceanic Sciences, University of Wisconsin—Madison, 1225 West Dayton Street, Madison WI 53706. Email: slhasten@wisc.edu

Abstract

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.

Corresponding author address: Stefan Hastenrath, Department of Atmospheric and Oceanic Sciences, University of Wisconsin—Madison, 1225 West Dayton Street, Madison WI 53706. Email: slhasten@wisc.edu

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