Extended Abstract (536K)9B.2
Does an instability of the African easterly jet generate African easterly waves?
Jen-shan Hsieh, Cornell University, Ithaca, NY
Many authors have suggested that the instability of the African easterly jet causes African easterly waves. Two numerical experiments using a mesoscale model (MM5) are performed to study the relationship between the jet and wave disturbances. The boundary conditions in the model are modified to produce two West African background climatologies, one with and one without the African easterly jet. The simulation with the jet shows realistic wave activity around 10N to 15N propagating off the west coast of Africa. The Charney-Stern and the Fjortoff stability conditions are both satisfied in the West African region and eastern tropical Atlantic, which indicates the jet instability may be a possible mechanisms of wave disturbances. However, the simulation without the African easterly jet also has realistic wave activity, with the waves originating near 25N and near 10N, similar to observations. The two wave paths merge over the tropical Atlantic. Comparison of the wave disturbances between these two simulations shows the wave disturbances without jet generally propagate slower than that with jet, which suggests that the jet speeds the wave propagation through advection.
These two MM5 simulations suggest that the instability of African easterly jet might not be the real cause of African easterly waves. The numerical simulation without the jet suggests that other factors, such as Sahara surface heating or the concentration of the ITCZ, may also contribute to the generation of African easterly waves.
Session 9B, Large-Scale Dynamics and Convection IV (Parallel with Sessions 9A, 9C, and 9D)
Wednesday, 1 May 2002, 11:00 AM-12:30 PM
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