Collaborative Research: Extratropical Transition of Tropical Cyclones Over the Western North Pacific--Physical Characteristics, Downstream Impacts, and Predictability

Naval Postgraduate School, Monterey CA

Investigators

Abstract

The movement of a tropical cyclone into the midlatitudes involves an interaction among complex physical processes. The extratropical transition (ET) of a tropical cyclone over the western North Pacific often causes a high-amplitude response that extends across the basin. Midlatitude circulations during an ET event can result in high-impact weather events over western North America ranging from strong coastal storms with severe coastline erosion in Alaska to "fire weather" in southern California. Furthermore, the downstream development from an ET event is often associated with reduced predictability. In this project, ET events will be studied in three regions: the decaying tropical cyclone core, the tropical cyclone-midlatitude interface, and the midlatitude impact region. The goals are to obtain increased understanding of the dependence of the occurrence, amplitude, and extent of the downstream response to an ET event the interactions between the decaying tropical cyclone and the midlatitude circulation into which it moves; to define the roles of the decaying tropical cyclone and the midlatitude flow in downstream development from an ET event; and to assess the impact of better represented ET in models on the prediction of downstream development. These goals will be achieved using a combination of modeling, observational analyses, and diagnoses. The observations will be gathered during the THe Observing systems Research and Predictability EXperiment (THORPEX) Pacific Asian Regional Campaign (T-PARC). Observing platforms include the Naval Research Laboratory (NRL) P-3 with the ELDORA radar and GPS dropwindsonde, the Deutsches Zentrum fur Luft- und Raumfahrt (DLR) Falcon with a Doppler wind lidar, water vapor lidar, and GPS dropwindsondes, and driftsondes with GPS dropwindsondes. Remotely sensed data include rapid-scan geostationary satellite products, microwave radiance data, and surface winds from scatterometers. These will be used to examine the structural features of ET events. A primary feature is the development of a strong anticyclone immediately downstream of the decaying tropical cyclone. This represents the initial perturbation of the midlatitude flow by the ET event. The influences of a suite of dynamical processes in explaining downstream development will be examined. Collaborations that involve use of two major numerical prediction systems will consider the sensitivity of forecast accuracy to the representation of an ET event. Broader impacts of this project include the potential for advancing operational forecasting for the benefit of society, which is one of the overall goals of THORPEX as endorsed by the 14th Congress of the World Meteorological Organization. The field phase of T-PARC will involve extensive student participation and education outreach.