An Eady model, modified by two Ekman layers of different strengths, is used to study analytically and numerically the behavior of strongly nonlinear, baroclinic waves. By means of a truncated spectral expansion, the model is reduced to a nonlinear autonomous system of equations which describes the dynamics of a single zonal wave number disturbance with its lowest two y-modes, and of the mean flow correction with its lowest four y-modes. Each y-mode consists of a baroclinic and a barotropic pattern. / Travelling steady waves, amplitude vacillation and structural vacillation are found in the model. / The transition from symmetric flow to steady wave flow is due to baroclinic instability of the symmetric flow with respect to a sin(pi)y-perturbation. Steady waves are stable when the flow is energetically balanced between baroclinicity and the Ekman dissipation through nonlinearity. / The transition from travelling, steady waves to amplitude vacillation is due to the baroclinic instability of the travelling, steady, sin(pi)y-wavy flow with respect to a sin(pi)y-perturbation. A typical amplitude vacillation is the vacillation of wave potential energy with time, via interference of nonlinear barotropic and baroclinic patterns of the lowest y-mode of the wave. / The transition from amplitude vacillation to structural vacillation is due to both the baroclinic instability of the vacillating, sin(pi)y-wavy flow with respect to a sin2(pi)y-perturbation and the nonlinear mode-mode interaction. This transition occurs gradually in a parameter region. A typical structural vacillation is the vacillation of the redistribution of wave kinetic energy in the meridional direction with time, via interference of the lowest two nonlinear y-modes of the wave. / Most vacillations in the atmosphere may be viewed as a mixed vacillation in the transition region from amplitude vacillation to structural vacillation. The possible applications of the mechanisms of amplitude vacillation and structural vacillation to the atmospheric vacillation are discussed. / The Ekman dissipation seems to play two roles: large amounts of dissipation are stabilizing, and small amounts of dissipation are destabilizing. / Source: Dissertation Abstracts International, Volume: 46-01, Section: B, page: 0200. / Thesis (Ph.D.)--The Florida State University, 1984.

A conformal transformation suggested by F. Schimdt is followed to implement a global spectral model with variable horizontal resolution. A conformal mapping is defined between the real physical sphere (Earth) to a transformed (Computational) sphere. The model equations are discretized on the computational sphere and the conventional spectral technique is applied to solve the model equations. / There are two types of transformations used in the present study, namely, the Stretching transformation and the Rotation of the horizontal grid points. Application of the stretching transformation results in finer resolution along the meridional direction. The stretching is controlled by a parameter C. / The rotation transformation can be used to relocate the North Pole of the model to any point on the geographic sphere. The idea is now to rotate the pole to the area of interest and refine the resolution around the new pole by applying the stretching transformation. The stretching transformation can be applied alone without the rotation. A T-42 Spectral Shallow-Water model is transformed by applying the stretching transformation alone as well as the two transformations together. A T-42 conventional Spectral Shallow-Water model is run as the control experiment and a conventional T-85 Spectral Shallow-Water model run is treated as the benchmark (Truth) solution. RMS error analysis for the geopotential field as well as the wind field is performed to evaluate the forecast made by the transformed model. It is observed that the RMS error of the transformed model is lower than that of the control run in a latitude band, for the case of stretching transformation alone, while for the total transformation (rotation followed by stretching), similar results are obtained for a rectangular domain. / A multi-level global spectral model is designed from the current FSU global spectral model in order to implement the conformal transformation. The transformed T-85 model is used to study Hurricane Andrew. The control experiment in this study is a conventional T-170 spectral model. The performance of transformed model is clearly seen to be improved in describing the structure, intensity and motion of Hurricane Andrew, over the conventional FSU global spectral model. / Source: Dissertation Abstracts International, Volume: 56-01, Section: B, page: 0295. / Major Professor: T. N. Krishnamurti. / Thesis (Ph.D.)--The Florida State University, 1994.

During the early phase of the numerical weather forecast, the initial analysis of the divergence plays an important role. However, using the conventional data analysis schemes, a successful initial analysis of the divergent circulation is difficult to achieve. It is proposed that over the convective regions, incorporating known convective heating information during the initialization can lead to an improved initial specification of the divergent circulation. Success of the proposed methodology depends on the efficiency of the initialization scheme. / For the dynamic normal mode initialization (DNMI) method used in the present study to perform the initialization, it is shown that this method does not succeed in initializing higher vertical modes. Since the assimilation of the convective heating into the initialized divergence crucially depends on the ability to initialize the correct vertical modes, use of DNMI would not be very appropriate. An improved initialization procedure where the DNMI is performed in the vertical mode space was then formulated. A comparison of initialization experiments performed with the conventional DNMI and the new scheme demonstrated that with the new initialization method, the initialization of the higher vertical modes could be better achieved. / The effects of including the convective heating during the initialization on the final initialized state were next explored. It is demonstrated that the dominant effect of the convective heating would be on the initialized divergence field. Further, it was illustrated that to some extent, the initialization with the specified convective heating can recover the corresponding divergent circulation in the initialized state. / The assimilation of the convective heating information into the initialized divergence was next put into use in a more practical setting. Using the satellite derived rainfall rates, it was confirmed that the initialization resulted in an improved structure of the divergence field associated with a typhoon. The improvements in the initialized divergence also reflect in other initialized fields (e.g. moisture convergence, initial rainfall). In the subsequent forecast, externally specified convective heating used during the initialization was merged with the model generated heating to keep the initialized divergence still in balance. It is shown that then the improvements in the initialized divergence also have positive impact on the subsequent forecast. / Source: Dissertation Abstracts International, Volume: 51-03, Section: B, page: 1319. / Major Professor: T. N. Krishnamurti. / Thesis (Ph.D.)--The Florida State University, 1990.

Quon's (1976) three dimensional semi-spectral, semi-grid point numerical model, simulating the thermally driven annulus experiments with flat bottom conducted at Florida State University's Geophysical Fluid Dynamics Institute, has been modified to include two-wave bottom topography and radially sloping bottom and top boundaries using $\sigma$ coordinates. With wave numbers 2, 4 and 6 as the only waves included, and with no wave-wave interactions, the new model has successfully exhibited the primary effects of both bottom topography and the equivalent $\beta$-effect due to the sloping boundaries on barotropic annulus flows. / These numerical simulations agree qualitatively with the laboratory experiments, in that as the rotation rate increases, the zonal jet changes from a single to a double jet structure and the upstream displacement of the topographically-forced wave increases. The former effect is more pronounced in the absence of sloping boundaries and the latter in the presence of such boundaries. It is also found that the maximum retardation of the zonal flow due to the topographic drag, takes place in the interior of the fluid around mid radius. / Our numerical simulations of baroclinic flows over two-wave topography have also captured the major features found in the laboratory experiments. In particular, topographically induced wave number 2 is found to be the dominant wave at the lowest rotation rate while traveling baroclinic wave numbers 4 and 6 become the dominant modes at higher rotation rates. We have also found that the zonal mean zonal current is stronger with topography present, which is interpreted as being due to the topographically induced low level heat flux which, as shown by Pfeffer (1987, 1992) can serve to accelerate the "westerlies". / Source: Dissertation Abstracts International, Volume: 56-12, Section: B, page: 6806. / Major Professor: Richard L. Pfeffer. / Thesis (Ph.D.)--The Florida State University, 1995.

Surface cyclogenesis in middle latitudes is preceded by the arrival of a pre-existing upper-tropospheric disturbance. Observational studies indicate that the preferred regions for the development of these upper-level troughs are characterized by weak low-level baroclinicity, large surface roughness and enhanced low-level stability. Linear instability calculations confirm that the development of baroclinic waves with maximum amplitude near the tropopause is favored when the low-level vertical shear is weak, while Ekman dissipation and low-level static stability are large. Conversely, when the low-level vertical shear is strong, while Ekman dissipation and low-level static stability are weak, the most unstable waves are surface concentrated. / It is hypothesized that surface cyclogenesis in the Northern hemisphere storm track regions can be described by the structural modification of baroclinic wave packets traversing a zonally varying flow field. This hypothesis is tested using a linear, quasi-geostrophic model with zonal variation in the basic state and the Ekman layer. The basic state consists of a region of strong low-level baroclinicity and weak Ekman dissipation, flanked by regions of weak low-level baroclinicity, strong Ekman dissipation, and enhanced low-level stability. Model calculations show that an isolated disturbance upstream of the mid-channel baroclinic zone evolves rapidly into a wave packet with maximum amplitude near the tropopause. Disturbances within the wave packet undergo a structural modification so that they have maximum amplitude at the surface within a few days of entering the mid channel baroclinic zone. The growth rate of an individual surface disturbance can exceed the growth rates of both the most unstable eigenmode of the zonally varying basic state and the most unstable eigenmode of a zonally homogeneous basic state characteristic of the mid-channel baroclinic zone. The surface cyclogenesis is due to the constructive interference between the several most unstable eigenmodes of the zonally varying basic state. The addition of a simple parameterization of latent heat release in the mid-channel baroclinic zone does not significantly alter the initiation of surface cyclones, but results in cyclones of smaller scale which undergo a longer period of rapid development. / Source: Dissertation Abstracts International, Volume: 51-12, Section: B, page: 5925. / Major Professor: Albert I. Barcilon. / Thesis (Ph.D.)--The Florida State University, 1990.

Source: Dissertation Abstracts International, Volume: 40-06, Section: B, page: 2714. / Thesis (Ph.D.)--The Florida State University, 1979.

Source: Dissertation Abstracts International, Volume: 40-06, Section: B, page: 2715. / Thesis (Ph.D.)--The Florida State University, 1979.

Source: Dissertation Abstracts International, Volume: 32-11, Section: B, page: 6567. / Thesis (Ph.D.)--The Florida State University, 1971.

Source: Dissertation Abstracts International, Volume: 32-11, Section: B, page: 6568. / Thesis (Ph.D.)--The Florida State University, 1971.

Source: Dissertation Abstracts International, Volume: 32-11, Section: B, page: 6568. / Thesis (Ph.D.)--The Florida State University, 1971.