Symmetrization, Vortex Rossby Waves, and Hurricane Motion in an Asymmetric Balance Model.
Abstract
The physical complexities of primitive equation (PE) models commonly used for forecasting hurricane track and structure changes can often make interpretation of their output difficult and speculative. A simplified balance formulation of these phenomena is desirable to further understand the physics of rapidly rotating storms. This thesis presents a shallow-water numerical model suitable for simulating hurricane track and evolution based on asymmetric balance (AB) theory. The model is a shallow-water formulation of AB, that incorporates rapid rotation and permits order-one divergence. The numerical solution technique employed is a pseudo-spectral azimuthal modes model utilizing grid points radially and Fourier modes azimuthally. In this work we also consider the problem of vortex axisymmetrization as a model for outwardly propagating spiral bands in hurricanes. The basic physics is illustrated most simply for stable vorticity monopoles on an f-plane. Unlike the dynamics of sheared disturbances in rectilinear shear flow, symmetrizing disturbances on a vortex are accompanied by outwardly propagating Rossby waves whose restoring mechanism is associated with the radial gradient of storm vorticity. Expressions for both phase and group velocities are developed and verified confirming early speculations on the existence of vortex Rossby waves in hurricanes. Effects of radially propagating waves on the mean vortex are also analyzed and the results suggest a new mechanism of vortex intensification. The theory is applied to a hurricane-like vortex in a shallow water asymmetric balance model and the results are in good agreement with observations. The vortex wave mechanics developed here shows promise in elucidating basic mechanisms of hurricane evolution and structure changes, such as the formation of secondary eyewalls.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 10, 1995
- Accession Number
- ADA299905
Entities
People
- Randall J. Kallenbach
Organizations
- Air Force Institute of Technology