Orographically Triggered Tropical Cyclones in the Eastern North Pacific

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Dr. Zehnder will continue to investigate the hypothesis that most cases of Eastern Pacific tropical cyclogenesis results from the interaction between easterly waves and the orography of Mexico and Central America. Under a previous award, he completed a case study of Hurricane Guillermo which suggests that orography played a strong role in the formation of the storm. The next phase of this research will involve analysis of ECMWF gridded data (composites), GOES data, and simulations with the MM5 model to further document the existence of orographically forced circulations and their role in tropical cyclogenesis. Using satellite data to identify areas of deep convection, Dr. Zehnder will construct composites of various fields for the prior 24-48 hour period from the ECMWF data sets. He will look for evidence of easterly waves and compare those cases where deep convective clusters developed into tropical cyclones and those when they did not. For the modeling component, he will carry out a number of idealized flow experiments to look at the roles of orography, easterly waves, and the North American monsoon trough.