Intermediate and high resolution simulations of the transition of a tropical wave critical layer to a tropical depression

Recent work has hypothesized that tropical cyclones in the Atlantic and eastern Pacific basins develop from within tropical wave critical layers. We begin a systematic test of the marsupial theory here by revisiting the classical problem of the transformation of an African easterly wave-like disturbance into a tropical storm. An idealized configuration of the Weather Research and Forecasting (WRF) model is employed using an initial zonal flow consistent with the observed zonal flow during Phase III of GATE and with recent NCEP analyses for the east Atlantic region. An analysis of the evolving winds, equivalent potential temperature, and relative vertical vorticity is presented from both intermediate and high resolution simulations. The results indicate the existence of a vorticity dominant region with minimal strain within the critical layer pouch that contains strong cyclonic vorticity and high saturation fraction and serves as the focal point for an upscale “bottom up” development process while the wave and pouch move together.