HR: 15:15h
AN: A43E-06    [Abstracts]
TI: Onset of the West African Monsoon: Role of Inertial Instability in the Monsoon Jump
AU: * Cook, K H
EM: khc6@cornell.edu
AF: Cornell University, Department of Earth and Atmospheric Sciences 3114 Snee Hall, Ithaca, NY 14853, United States
AU: Hagos, S M
EM: sh282@cornell.edu
AF: Cornell University, Department of Earth and Atmospheric Sciences 3114 Snee Hall, Ithaca, NY 14853, United States
AB: The West African monsoon jump is a sudden change in the position of the rainfall maximum over the continent in boreal summer. Through the spring, the precipitation maximum lies over the Guinean coast near 5°N. At this time, the hydrodynamics is closely tied to the ocean environment of the Gulf of Guinea, similar to the Atlantic marine ITCZ. In June or July the dynamics changes over the course of a few days and the precipitation maximum is repositioned much farther inland, near 12°N over the Sahel. Since the presence of the land surface is responsible for the occurrence of the jump, it can also be termed the monsoon onset. The dynamics of the monsoon jump is studied using a regional atmospheric model in two simulation designs. In one, the West African monsoon system is represented in a climatological context, with prescribed time-mean lateral and surface boundary conditions and 90-km resolution. In the second design, which is part of the West African Monsoon Modeling and Evaluation (WAMME) program, both the climatology and 5 individual (2002-2006) years are simulated with higher resolution (50 km) and an interactive land surface. The monsoon jump is captured realistically in the model. The dynamics of the jump is found to be related to the development of inertial instability over West Africa in the summer, when strong meridional geopotential height gradients develop in late spring/early summer. The role of the monsoon jump in the interannual variability of the monsoon is discussed.
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 3354 Precipitation (1854)
DE: 3355 Regional modeling
DE: 3374 Tropical meteorology
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly