Stratiform precipitation production over sub-Saharan Africa and the tropical...

Schumacher, C., and R. Houze (2006), Stratiform precipitation production over sub-Saharan Africa and the tropical East Atlantic as observed by TRMM, Q. J. R. Meteorol. Soc., 132, 2235-2255, doi:10.1256/qj.05.121.

Convective systems over sub-Saharan Africa and the tropical East Atlantic have distinct geographical and seasonal variations in convective intensity and stratiform precipitation production as observed by the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar. Over the East Atlantic, convective rain rates are lower and the percentage of total rain that is stratiform is higher compared to over West Africa. In addition, the East Atlantic has more shallow precipitating convection and less non-precipitating anvil than sub-Saharan Africa. During the monsoon season, convective rain rates and the percentage of area covered by anvil decrease while the stratiform rain fraction and number of shallow convective cells increase in both regions compared to the pre-monsoon season. These observations suggest that convective sustainability, i.e. the ability of a region to continually support convection, helps determine whether a robust stratiform rain area or non-precipitating anvil forms.

In addition to convective sustainability, wind shear and the Saharan Air Layer appear to play important roles in the formation and extent of the stratiform components of convective cloud systems. Strong winds associated with the African Easterly Jet and dry intrusions from the Sahara Desert may increase sublimation and evaporation at mid levels, resulting in less stratiform rain. Strong upper-level shear associated with the African Easterly Jet may further hinder stratiform rain production by displacing hydrometeors that form in the convective cells beyond the area of mesoscale rain formation. When the upper-level Tropical Easterly Jet strengthens during the monsoon season, upper-level shear is reduced dramatically and stratiform rain areas form in preference to non-raining anvil.

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