This dissertation extends the Nonlinear Normal Mode initialization procedure to situations where the current methods encounter problems (convergence of iteration, and reduction of divergent circulations). / A simple interpretation of the current schemes is first introduced, in which the iterative schemes are regarded as sequential applications of filters. The response function of these filters provide a means to evaluate the convergence of the iterative methods. The current iterative schemes are found to be sensitive to the accuracy of the estimate of the smallest time scales (arising from the eigenvalue decomposition) present in each mode. If the estimate is accurate the schemes do well; if inaccurate, they do poorly. A new technique (identified as the Pseudo-Secant or PS method) is introduced. The new scheme determines the smallest time scale for each mode is adaptively. The technique is compared with current techniques (the schemes suggested by Machenenhauer, Tribbia, and Kitade) in two models. The first model, originally introduced by Tribbia, represents a very simple simulation of axi-symmetric flow in which the analytic solution is known. The PS method is shown, for this model, to converge more quickly in the presence of strong forcing, and for a much larger range of forcing than others. The second set of calculations uses a model of equivalent sophistication and complexity to the operational forecast models used throughout the world today. Comparisons between schemes are made in terms of success in attaining a balance, maintenance of the Hadley circulation, differences between the fields prior and following the initialization, and differences between the model defined balance and those defined by the initializations. The PS scheme is shown to converge (find a good balance) in the presence of parameterizations of diabatic processes which cause the other schemes to diverge. The Hadley circulation is maintained during this initialization. The balance is defined by any of the initializations differ from that defined by the model itself. / The use of a diabatic initialization makes only marginal improvements in the forecast skill, compared to an adiabatic initialization, when examined in terms of a simple predictability study. / Source: Dissertation Abstracts International, Volume: 45-02, Section: B, page: 0586. / Thesis (Ph.D.)--The Florida State University, 1984.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_75282 |
| Contributors | RASCH, PHILIP JOHN., Florida State University |
| Source Sets | Florida State University |
| Detected Language | English |
| Type | Text |
| Format | 156 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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