131 What convective properties are most critical for tropical cyclogenesis? Evidence from a multi-satellite investigation of developing and nondeveloping disturbances

Thursday, 3 April 2014
Golden Ballroom (Town and Country Resort )
Jonathan Zawislak, University of Utah, Salt Lake City, UT; and E. Zipser

Though deep convection has invariably been identified as a necessary component of tropical cyclogenesis and intensification, the relative importance of various convective properties in those processes continue 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 passive microwave platforms (including TRMM, AMSR-E, and SSM/I[S]) from 138 (128) developing and 151 (67) nondeveloping disturbances in the Atlantic (East Pacific) basin between 2005 and 2012. The developing sample consists of the nearly all tropical cyclones during those seasons, while the nondeveloping sample is comprised of nearly all disturbances classified as “invests” by the National Hurricane Center. Results will be computed for the best track center locations (archived in the Automated Tropical Cyclone Forecasting [ATCF] system), which will be used in lieu of vorticity and pouch centers. Overall this study will offer a detailed analysis of the time evolution of convective events multiple days before genesis, while also offering a rare opportunity to determine whether the properties of convection during the pre-genesis stage of developing disturbances are unique compared to those observed in nondeveloping disturbances. By evaluating proxies for convective intensity, raining area and proximity to the disturbance center, results may lend support to the hypothesis that the fractional coverage of precipitation near the center – not necessarily intensity – is most critical for genesis to occur, while also providing insight into whether particular convective properties differentiate disturbances that, once the large-scale environment is favorable, form “quickly” (after 1-2 convective burst periods) versus disturbances that go through multiple convective events prior to formation. The study will also determine whether there are significant differences in the properties of convection involved in tropical cyclogenesis in the Atlantic and East Pacific basins, as well as across various subregions of the Atlantic basin (i.e., Gulf of Mexico, Caribbean, Central Atlantic, and East Atlantic). Finally, by synthesizing information on the time evolution of convective properties with PMW-derived measurements of moisture content (and humidity, when available from AIRS), 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.
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