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.
