P3.13
African Easterly Waves: dynamical stability and possible precursors
Nicholas Hall, LEGI, Grenoble, France; and A. Diedhiou
African Easterly Waves are an intermittent phenomenon that grow over west Africa and propagate out into the Atlantic with a period of about 5 days. They are active during the west African wet season and play an important role in modulating the precipitation. AEW events are also implicated in the genesis of huricanes.
In this paper we use a primitive equation model to study the growth of AEWs on a selection of three dimensional basic states taken from reanalysis data using composites of observed episodes of AEW activity. The simulated waves grow by baroclinic conversions but are relatively insensitive to the range of baroclinicity observed in the data. In fact, with a modest amount of surface friction the basic states are not even unstable and the waves decay exponentially.
We therefore hypothesise that possible precursors to these systems should be sought not in the stability of the African easterly jet, but in the forcing or in pre-existing systems. Our simulated waves are forced by a low-level heating anomaly. After constructing influence functions to find the optimal location for such a forcing, we return to the data to seek possible precursors to observed wave composites.
Poster Session 3, Poster Session III
Thursday, 13 February 2003, 9:45 AM-11:00 AM
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