Department of Environmental Sciences
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Seminar Abstracts
Environmental Sciences Seminar Abstract            

  Tropical Cyclogenesis in a Tropical Easterly Wave Critical Layer
Zhuo Wang
Naval Postgraduate School, Monterey, California

A new paradigm for formation of a tropical cyclone within the critical layer of a tropical easterly wave is proposed. The critical layer of a tropical easterly wave is important to tropical storm formation because: H1) wave breaking or roll-up of the cyclonic vorticity and lower-tropospheric moisture near the critical surface provides the moist vorticity seedling for TC formation; H2) the critical layer is a region of approximately closed Lagrangian circulation, and air is repeatedly moistened by convection and protected to some degree from dry air intrusion; H3) the parent wave is maintained and possibly enhanced by diabatically amplified mesoscale vortices within the wave critical layer. The entire sequence is likened to the development of a marsupial infant in its mother's pouch wherein the juvenile proto-vortex is carried along by the mother wave until it is strengthened into a self-sustaining entity. A survey of 55 named storms in the Atlantic and eastern Pacific sectors during August-September 1998-2001 using three independent datasets is shown to support the marsupial paradigm.

The marsupial paradigm is tested using the high-resolution simulation of the genesis of pre-Hurricane Felix (2007). A diagnosis of the model simulation supports key elements of the marsupial paradigm by demonstrating the existence of a rotationdominant region with minimal deformation within the wave critical layer that contains strong cyclonic vorticity and high saturation fraction. This localized region serves as the focal point for an upscale "bottom up" development process while the wave and pouch move together. Based on the marsupial paradigm, real-time forecast products are developed to predict the genesis location using global model operational data. The genesis location can be predicted up to three days in advance with an error less than 200 km, which can provide useful guidance for forecasters and flight planning.


Last updated: 03/10/2009