Collaborative Research: Basic Studies in Three-dimensional Tropical Cyclone Intensification

Northwest Research Associates, Incorporated, Seattle WA

Investigators

Abstract

Hurricanes are especially destructive tropical weather systems that threaten population centers of the United States along the Atlantic coast between June and November every year. Well-developed hurricanes display a relatively high degree of geometrical organization in their core region, with a central cloud-free eye surrounded by an approximate ring of clouds, called the eyewall, where the most intense surface winds are found. Existing theories for hurricane structure have exploited this geometric organization in the framework of axial symmetric circulation and these approaches have provided useful insights into this destructive phenomenon. This funded project aims to gain a better understanding of the roles of axial asymmetries or "eddy" processes in the intensification of tropical cyclones. This research project will focus on the dynamics and thermodynamics of eddy processes in hurricanes using an integrated, multi-pronged evaluation of the internal eddy processes during the intensification stage of tropical storms. Specifically, the PIs will conduct diagnostic analyses to evaluate the impact of the eddy structures on the axial symmetric component of tropical storms by employing conventional Eulerian analyses and a new analysis method based on Lagrangian coherent structures. Lagrangian coherent structures help identify structures within the wind flow that tend to separate the flow into distinct regions. These regions will aid in the identification of momentum and heat transport by the eddies. High resolution computer simulation will be the foundational tool in this study, and the ability to resolve and analyze the important eddies at different computer resolutions will be investigated. This research is of interest to atmospheric science, fluid dynamics and dynamical system communities. The determination of the manifold roles of various eddy phenomena on the mean hurricane structure is of high intellectual merit. Improved characterization of the effects of eddies on the wind structure and intensity of hurricanes will serve as useful guidance in the development of future parameterizations. Since operational models do not well resolve these fine-scale features, the improved understanding of the importance of eddy processes for the rapid intensification of tropical storms would help further increase the skill in predicting the substantial hazard posed by hurricanes.