Doctor of Philosophy

Abstract

dissertationThis dissertation attempts to detail the necessary and sufficient conditions for tropical cyclogenesis; specifically those environmental, convective, and thermodynamic properties that may determine the fate of disturbances with apparent genesis potential. Unlike previous observational case studies which evaluate a few cases with limited spatial and temporal resolution in-situ and satellite data, this study examines 1 2 developing and four nondeveloping cases from recent (since 2005) tropical cyclone field campaigns using dropsonde data from multiple agency aircraft, as well as data from infrared and multiple passive microwave satellite platforms. Results, composited for all developing cases, indicate that the inner core of developing disturbances prior to genesis exhibits a midlevel moisture that is greater than the surrounding environment, high relative humidity, a warm temperature anomaly at upper levels that progressively lowers through genesis, and a cool, dry anomaly at low levels. Likewise, the vertical alignment of the low- and midlevel vorticity centers is necessary for formation. The midlevel moisture content only shows a slight "progressive moistening" during the pregenesis stage, while the total precipitable water does not apparently increase among the cases studied. Consistent with conclusions from previous observational and modeling studies, the cool, dry anomaly and increased static stability at low levels in the composite, perhaps as a result of persistent convective precipitation near the center within 1-3 days of genesis, appears to be a necessary condition for formation; this genesis pathway suggests that an initially stronger midlevel vortex precedes primarily low-level spin-up within a day of formation. Among the convective properties examined using the satellite datasets (raining area, convective intensity, area of intense convection, duration, and proximity), the results suggest that the proximity and duration of precipitation within three degrees of the center are the most important properties for formation. However, the developing cases studied do not exhibit any common distinguishing convective characteristics during the pregenesis stage; not all developing cases exhibit widespread, intense convective episodes, and although some of the cases exhibit their most "favorable" convective episodes (in terms of intensity, area, and proximity to the center) around 30-36 hours prior to formation, in a few cases that episode occurs as many as 3 days before formation