SUDDEN CHANGES IN UPPER TROPOSPHERIC WIND DIRECTIONS OVER THE WEST AFRICAN SAHEL

Abstract

The aim of the research is to investigate sudden change in direction of upper tropospheric winds over the West African Sahel. Specifically the objectives are to determine the cause of the persistent westerlies observed over the region, prior to the sudden change and; to determine the transport of momentum responsible for the change. The investigation was conducted using a 30-year data of the zonal and meridional wind, and vertical velocity obtained from ERA Interim Daily Fields at a resolution of 1.50 ×1.50. The data set were used in computing transient momentum and the transport thereof, and thesewere then subsequently presented as time series superimposed on the corresponding wind direction (which were computed from the values of the zonal and meridional wind). The observation and analysis of the trends therein indicate that the sudden change is as a result of transport of transient easterly momentum mostly by northward meridional wind anomalies. The results also revealed that the persistent westerlies are driven by meridional advection and downward transport of westerly transients, while the easterlies observed in the wake of the sudden change are mostly maintained by upward transport of transient easterly momentum.