Tropical Cyclogenesis in the PRE-depression Investigation of Cloud-systems in the Tropics program (PREDICT): The Marsupial Paradigm in Action

Northwest Research Associates, Incorporated, Seattle WA

Investigators

Abstract

Intellectual Merit: Tropical cyclogenesis remains one of the outstanding mysteries of the tropical atmosphere, yet a proper understanding of how hurricanes and typhoons are born is the first of several steps in relating the effects of climate change on these storms and the impact of severe weather on coastal regions of eastern North America. Fundamentally a mesoscale process, tropical cyclogenesis integrates the large-scale circulation, synoptic waves, and mesoscale processes (ranging from critical layer formation in tropical waves to vortical hot towers on the cloud scale) into a hurricane monolith at intermediate scales (20-200 km). Although many of the relevant dynamical and thermodynamical processes at this scale have been investigated, virtually nothing is known about their relative importance, chronological sequence and mutual interaction in the various stages of tropical cyclogenesis. A field campaign (PRE-depression Investigation of Cloud systems in the Tropics; PREDICT) has been designed to obtain in situ measurements of mesoscale processes in developing tropical depressions in the western Atlantic. Data from the PREDICT field campaign will be analyzed in conjunction with operational and retrospective meteorological analyses, short-term forecasts and satellite imagery in order to address mesoscale issues and the interaction of physical processes across multiple scales. A new "marsupial paradigm" developed by the Principal Investigator and colleagues at the Naval Postgraduate School will be applied in real time to the PREDICT data acquisition and interpretation efforts. This paradigm focuses on the role of the tropical wave critical layer (outer mesoscale, 200-2000 km) in genesis, and on key environmental conditions that are necessary for development within the "gyre-pouch" of a parent wave. This study is concerned mainly with mesoscale processes operating in the gyre-pouch, and how these processes are affected by environmental conditions nearby and within. A null hypothesis of PREDICT is that mesoscale processes do not vary across a wide range of synoptic patterns in which tropical cyclogenesis occurs. According to this idea, it is the precise way that mesoscale processes interact with, and within, the gyre's moist vortical environment that determines whether storm development is successful. The marsupial paradigm provides the necessary Lagrangian framework for interpretation of high-resolution atmospheric data and for improved understanding of processes. Post-analysis of field data will be integrated with large-scale analyses to refine and extend the marsupial paradigm. Broader Impacts: Public education on severe weather is important to help society utilize weather information and to help them understand their environment. A longer-term concern is to understand how our changing climate has, and will, affect these storms and their impacts. An improved scientific understanding of how to interpret the data input stream will be passed on to the public in terms of a more reliable classification of storm status and better prediction of the likelihood of storm formation and intensification when these systems, in many cases, are still far from land.