What Precipitation Properties Are Most Critical for Tropical Cyclogenesis? Evidence from a Multi-Satellite Investigation of Developing and Nondeveloping Disturbances

Abstract:

The relative importance of deep convection in tropical cyclogenesis continues to be debated among observational and modeling studies. This study will contribute to the observational dataset by providing a comprehensive collection of satellite observations from multiple passive microwave platforms, as well as the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar. The case sample consists of 10 years (2003-2012) of developing (348 cases) and nondeveloping (320 cases) disturbances in the Atlantic, East Pacific, and Central Pacific basins. Nondeveloping disturbances are identified as those disturbances that do not exceed an “invest” classification by the National Hurricane Center. Overall this study will offer a detailed analysis of the properties of both convective and stratiform precipitation multiple days before genesis, while also offering a rare opportunity to determine whether the properties of precipitation at, and just prior to, genesis are unique compared to previous days of the pregenesis stage. By evaluating proxies for convective intensity, raining area and proximity to the disturbance center, results may lend support to the hypothesis that genesis is more closely tied to the fractional coverage of precipitation near the center - not to “intense” convection. The study will also determine whether there are significant differences in the properties of precipitation involved in tropical cyclogenesis among the Atlantic, East and Central Pacific basins, as well as across various subregions of the Atlantic basin. Finally, by synthesizing information on the evolution of precipitation properties with PMW-derived measurements of moisture content (and humidity, when available), a specific emphasis is placed on quantifying moistening within the inner core of the developing disturbances and critically evaluating the hypothesis that a progressive humidification of the midlevels is observed as genesis nears.