A Climatology of Cold Surges along the African Highlands

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Sunday, 4 January 2015
Caitlin Crossett, Hobart and William Smith Colleges, Geneva, NY; and N. D. Metz

Equatorward moving cold surges are ubiquitous features along the lee of high terrain, especially during the cold season. These cold surges have been studied along many mountain ranges including, the Andes, Appalachians, Rockies, and Himalayas. However, even though the east coast of Africa features high terrain, a dearth of research exists on cold surges along the African Highlands despite the fact that the surges can have potentially large agricultural effects. The purpose of this presentation is to examine these African Highlands cold surges from a climatological perspective.

A five-year climatology of African Highlands cold surges was created spanning the 2008 to 2012 period following a similar methodology used by Lupo et al. (2001) for cold surges occurring along The Andes. This climatology contains almost 150 separate cold surge events and reveals that African Highlands cold surges have a climatological maximum in September. The strongest events tend to occur throughout the Southern Hemisphere winter. These cold surges can be associated with 925-hPa temperature declines in excess of 15C, as 925-hPa southerly meridional flow advects Antarctic air equatorward. Cold air signatures and ageostrophic flow from these cold surges can be traced, in some instances, all the way north to the equator. Cold surges in the climatology were found to last up to fifteen days, with the highest frequency of events spanning a three-day period.