Wave Dynamics in Tropical Cyclones

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Intellectual Merit: In several stages, this project will build a framework for interpreting the complex wave dynamics that are believed to partially regulate hurricane intensity. Stage 1: Previous theories of wave dynamics neglected clouds within the hurricane. Such neglect is difficult to justify, because regions with dense cloud coverage, such as the eyewall, have greatly reduced static stability. The first stage of this project will examine the influence of cloud coverage on waves and wave-mean-flow interactions in a relatively simple model. Specifically, the investigators will examine waves in a gravitationally stable, nonprecipitating cloudy vortex that has no mean secondary circulation and does not interact with the planetary boundary layer. Starting from first principles, the investigators have derived a set of linearized wave equations for this system. Furthermore, they have begun to examine (analytically and computationally) how cloud coverage affects eyewall instability and internal gravity wave radiation. These two processes are of interest because they can in principle alter the maximum mean tangential wind speed of the vortex. Stage 2: The second stage of the project will complement the first with less approximate computational experiments. The main tool will likely be the Regional Atmospheric Modeling System (RAMS), developed at Colorado State University. The investigators plan to use RAMS to (i) independently verify results from Stage 1, and (ii) examine nonlinear wave phenomena in an idealized cloudy vortex. Stage 3: The investigators anticipate a third stage of the project, in which they will continue use of RAMS to study how additional factors, such as precipitation, mean secondary circulation and boundary layer fluxes of enthalpy and angular momentum affect the wave dynamics. Broader Impacts: The research effort will lead to collaborations between modeling specialists, observational meteorologists and applied mathematicians. In addition, results will be immediately incorporated into advanced graduate level courses at Colorado State University.