Cold Surges along the African Highlands
A five-year climatology of African Highlands cold surges was created spanning the 2008 to 2012 period. This climatology revealed that African Highlands cold surges had a climatological maximum in September, and the strongest events were featured throughout the Southern Hemisphere winter. These cold surges feature temperature drops of between 2°C and 11°C, as 925-hPa meridional flow averaging 35 knots advected Antarctic air equatorward. Cold surges along the African Highlands last from one, to fifteen days, with the highest frequency of events spanning a three-day period. A representative case study reveals that during a cold surge event, a surface anticyclone forms near the southern coast of Africa in a favorable region of subsidence, associated with quasi-geostrophic forcing for descent. As the anticyclone progresses eastward, 925-hPa winds become southerly and ageostrophic as they advect cold air equatorward along the lee of the African Highlands.