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This study will examine scale interactions and energy transformations that occur during hurricane genesis. A high-resolution mesoscale model that uses initial and boundary conditions obtained from the National Centers for Environmental Prediction (NCEP) Global Final Tropospheric Analyses and that produces a reasonable simulation on hurricane genesis will be employed. We will first explore the organization of convection during hurricane genesis to establish which scales are evolving and to determine which wavenumbers constitute the hurricane scale. Next, complete energy budgets during hurricane genesis will be examined. This is aimed at sorting out energy flow during hurricane genesis. The framework of the study is based on the seminal papers by Saltzman (1957, 1970) on atmospheric energetics in the wavenumber domain. A complete energy budget includes examination of the generation of available potential energy, conversion from available potential energy to eddy kinetic energy, the rate of change of kinetic energy due to nonlinear triad interactions, the rate of change of potential energy due to nonlinear triad interactions, zonal to waves flow of kinetic energy, and zonal to waves flow of potential energy. The main findings of this study are that individual cloud elements and cloud clusters are evolving into larger scale (symmetric) clusters around the eye of the hurricane and that a hurricane's scale can be described by wavenumbers 0, 1, and 2. The largest contributor to the energy exchange was found to be both of the in-scale quadratic nonlinearities, particularly the baroclinic conversion from available potential energy to kinetic energy. The transfer of energy between the different scales are small compared to the in-scale energy exchanges. The generation of available potential energy for the hurricane scale increases during hurricane genesis indicating the organization of clouds along the hurricane scale. The conversion of available potential energy to eddy kinetic energy mirrors the generation of available potential energy and indicates that the warm core of the storm is building up. In particular, it was found that conversion to KE due to vertical overturnings was important on the cloud scale during the formative stage of the hurricane. By the hurricane stage, the cloud scales became less important while the largest conversion occurred among the mean. The general pattern is for the mean and the large-scale asymmetries to lose available potential energy to the cloud scales indicating a down-gradient sensible heat flux. The kinetic energy exchanges between the different scales tend to be slightly smaller than the exchanges of available potential energy and are more variable. During the formative stage the general pattern is for the mean to lose kinetic energy to the large-scale asymmetries. By the hurricane stage, the exchanges between the mean and the large-scale asymmetries are similar in magnitude, but the patterns are inconsistent. However, it was found that the cloud scales receive the bulk of the KE during the hurricane stage.
A Dissertation Submitted to the Department of Meteorology in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy.
Includes bibliographical references.
Florida State University
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