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.