Conditions for the formation of deep convective activities over Nigeria

Abstract

Some mean flow parameters and dynamic processes necessary for the formation of widespread deep convective activities over Nigeria have been investigated and their interactive roles identified. These parameters include the low-level and the 700mb winds known as African Easterly jet (AEJ), spatial distribution of the vertical shears variability of the Zonal and meridional winds, the spatial and temporal of the height of the moist layer, and the anomalies of equivalent potential temperature and specific humidity. Wide spread thunder storms and/or organized line squalls were fond to exist on days of well defined African Easterly Jet (AEJ) with a higher concentration of storms/squalls around the left entrances and right exists in contrast with the middle latitude situation where weather development is normally expected around the right entrances and left exits of jet streams. Positive (westerly) low-level (boundary layer) zonal and meridional wind shears were found to be more important to storm initiation due to their overturning effects. On the other hand, negative (easterly) low-level shears led to suppression of convective activities. The depth and strength of convective activities were found to be affected by a deepening of the moist layer (represented by the height of the positive meridional (V) components of the wind) in the preceding twenty-four hours. A reasonably deep layer of moisture of at least 1.5km favours widespread deep convection.
Mappings of positive vertical wind shears height of the moist layer greater than 0.5km were found to have very high correlation with areas of line squall/thunderstorm occurrence while anomalies of the equivalent potential temperature and specific humidity gave minimal correlation with convection.

Key Words: Thunder storms, Line Squall, African Easterly Jet, Wind Shears, Convection.


(Global Journal of Pure and Applied Sciences: 2002 8(3): 411-417)