The nocturnal low-level jet in tropical West Africa: generation and representation in various data archives

Like many regions, tropical West Africa often experiences a low-level jet stream after sunset. In general, such jets are believed to be produced as a response to the sudden decrease in turbulence in the boundary when daytime heating ceases. However, the nocturnal low-level jet in West Africa exists in a complex environment in which (a) the boundary layer rarely gets especially stable at night, (b) the Coriolis force is extremely weak, and (c) the pressure gradient force has a particularly large diurnal cycle (due to the formation of a heat low to the north of the region). In this study, the nocturnal low-level jet is examined using radiosonde and UHF wind profile data gathered during the AMMA (African Monsoon Multidisciplinary Analyses) field campaign in 2006. These data, as well as output from a WRF simulation of the region, are used to quantify the forces at work at different levels of the atmosphere to explain the formation, maintenance, and dissipation of this feature of the monsoon circulation.