Interactions of Upper Level Troughs and African Easterly Waves

Tropical cyclone formation from African Easterly Waves (AEWs) has long been studied by meteorologists. Tropical meteorologists have also closely examined the impact of upper level troughs on the intensity of tropical cyclones. However, very few studies have examined the interaction of upper level troughs with AEWs . From a conceptual perspective, one might perceive upper level troughs to interact negatively with AEWs, mainly due to increased vertical wind shear. However, as previous studies of interactions of upper level troughs and tropical cyclones indicate, these upper level troughs may actually strengthen tropical disturbances via potential vorticity superposition and inward propagating eddy momentum flux convergence, allowing for an increased outflow channel aloft and in turn increased convergence at the surface. Examining these interactions is important from a predictability sense, allowing forecasters to better anticipate the development or non-development of an AEW as a result of interactions with synoptic mid-latitude systems.

In this study, a database of upper level troughs interacting with AEWs are acquired from reanalysis datasets. The cases of interacting AEWs with upper level troughs are compared to the National Hurricane Center best track data in order to determine which interacting AEWs and upper level troughs led to a tropical cyclone. Preliminary results from several diagnostics seem to indicate upper level troughs tend to be detrimental to tropical cyclogenesis, with a few exceptions.

Several cases of developing and non-developing cases are then initialized into the Weather Research and Forecasting Model (WRF) to provide better dynamical understanding for each of these cases. The model results are compared to the reanalysis data in order to determine whether WRF was able to successfully model the impact of the upper level trough on tropical cyclogenesis for the various cases of interest.