A hurricane is a threat to socio-economic activities in coastal communities bordering the South Atlantic Ocean (SAO). Hurricanes rarely form over this region and as such these communities are not prepared for them. Previous studies have suggested that anthropogenic warming may lead to more frequent hurricanes over the region and have demonstrated the capability of the Weather Research and Forecasting model (WRF) in capturing the impacts of the warming on hurricanes. However, none of the studies have investigated how the model's horizontal resolution and boundary forcing could alter the characteristics of simulated hurricanes. The present study used WRF to perform a series of experiments to simulate two hurricanes (Hurricane Catarina and Hurricane Anita) over the SAO at three horizontal resolutions (3.3 km, 10 km, and 30 km), using two reanalysis datasets (ERA-Interim (hereafter ERAINT) and NCEP CFSR (hereafter CFSR)) as the boundary forcing data. The performances of the reanalysis and WRF are compared with observational data from the International Best Track and Archive for Climate Stewardship. The results show that both reanalyses datasets give a good representation of the two hurricanes, but they grossly underestimate the intensity thereof. CFSR gives a better representation than that of ERAINT. However, both reanalyses also suggest that the South Atlantic Convergence Zone may be the moisture belt for hurricane formation over the SAO. WRF gives a credible simulation of the hurricanes. In simulating Hurricane Catarina, WRF performs best at a 10-km resolution; but in reproducing Hurricane Anita, the model performs best at a 3.3 km resolution. For both cases, the model performs better when forced with ERAINT than with CFSR. Hence, the study shows that increasing the resolution of the model may not necessarily improve the simulated hurricane over the SAO, and that, the quality of the simulated hurricane depends on the dataset that provides the boundary forcing. The results of the study have improved the understanding of hurricane characteristics in the SAO, and have shown the potentials of WRF to forecast and project future events as well as for downscaling the potential impacts of future climate change on hurricanes over the SAO.

Tropical Cyclones are one of the most devastating natural phenomena. Previous attempts to simulate Tropical Cyclones (TCs) over the South West Indian Ocean (SWIO) have used Global Circulation Models (GCMs) with uniform grid. This study examines the capability of a GCM with adaptive grid stretching (CAM-EULAG, hereafter CEU) in simulating the characteristics of TCs over the SWIO. In the study, the CEU model is applied with a fine horizontal grid resolution (0.5°x0.5°) over the SWIO and coarser resolution (1°x1° - 2°x2.25°) over the rest of the globe. The model simulation is performed for 11 years (1999-2010) and validated against the Joint Typhoon Warning Centre (JTWC) best track observation, Global Precipitation Climatology Project (GPCP) satellite data, and ERA-Interim (ERAINT) reanalysis data. The study also considers the impact of El Niño Southern Oscillation (ENSO), Indian Ocean Dipole (IOD) and the South Atlantic Subtropical Dipole (SASD) on TC counts over the SWIO.

The stability-corrected aerodynamic method was used to estimate fluxes of sensible and latent heat over an irrigated winter wheat field at Maricopa Agricultural Center in southern Arizona. These estimates were compared against the more precise Bowen ratio energy balance measurements made at the same location. The data were collected for 43 consecutive days over a range of canopy conditions. The aerodynamic method performed poorly against the validated Bowen ratio method at this site. Fluxes of latent heat were underestimated by the stability-corrected aerodynamic method. Sensible heat fluxes sometimes agreed well, but were often low. A new model was developed by combining AERO sensible heat (H(aero) with net radiation and soil heat flux to estimate latent energy as a residual (Le(resid)) in the surface energy balance equation. This aerodynamic energy balance (AEB) method, produced R² values of 0.97 and 0.78 for the wet and dry periods respectively.

This study examines interactions between tropical cyclones and the nearby environment as the cyclone leaves the tropics. It proves the hypothesis that any asymmetry in the structure of a tropical cyclone can perturb the track. The study employs data from a primitive equation global spectral model and two observational studies. Results indicate the environment can modify the cyclone structure with significant impact on track. There are two levels of interaction. Strong interactions occur when the cyclone absorbs mid-latitude weather systems into its circulation. Trajectory analyses confirm the mid-latitude origin of the air parcels in the strongest case presented here. This process produces major changes in the vortex structure and track. These interactions can help or hinder recurvature depending on the interaction geometry. Weak interactions occur when the vortex is slightly modified. They produce smaller track changes than strong interactions. Another case shows an interaction with the monsoon trough, and this proves any interaction can perturb the vortex structure. Three cases indicate that recurvature processes start at the top of the cyclone and work down. The study also shows the existence of barotropic beta gyres in both model and observational data. These are most apparent when the cyclone is not interacting with other weather systems. Interactions with other systems produce perturbations in the vortex that make beta gyres insignificant. / Source: Dissertation Abstracts International, Volume: 55-09, Section: B, page: 3936. / Major Professor: T. N. Krishnamurti. / Thesis (Ph.D.)--The Florida State University, 1994.

Radiative transfer simulations are performed in three phases to determine how water vapor and clouds affect passive brightness temperatures ($\rm T\sb{B}$ scS) of moisture sounding channels on the Advanced Microwave Sounding Unit (AMSU). Phase 1 employs idealized profiles of water vapor, cloud liquid water, and cloud ice as input to the radiative transfer model to investigate how AMSU frequencies at 23.8, 89, 157, 176, 180 and 182 GHz respond to clear and cloudy non-precipitating atmospheres. Phase 2 represents an effort to verify the microwave radiative transfer approach using observed data from an aircraft-mounted prototype radiometer. Phase 3 of the research employs output from a mesoscale model simulation of the ERICA IOP4 cyclone in an effort to gain insight about the synoptic interpretation of microwave water vapor image signatures. Model soundings are used in the radiative transfer code to generate synthetic 182 GHz imagery, as if a satellite were viewing the model atmosphere. / In Phase 1, $\rm T\sb{B}$ scS at 23.8 GHz and 89 GHz are more strongly affected by "altostratus" liquid clouds than by "cirrus" clouds for equivalent water paths. Channels near 157 and 183 GHz are more strongly affected by ice clouds. Phase 2 results indicate that the radiative transfer approach is adequate for simulating observed $\rm T\sb{B}$ scS, and that $\rm T\sb{B}$ scS at the relatively high microwave frequencies considered here are very sensitive to the ice particle size distribution. Phase 3 results show that 50% of the radiance contribution at 182 GHz for clear atmospheres emanates from the upper 0.35 mm of precipitable water, that is, above 380-400 mb, while 90% comes from the top 1.5 mm. A warm radiometric feature occurs near a tropopause fold. Dry upper and middle tropospheric air over the extremely dry formerly stratospheric air brought down by the tropopause fold allow the simulated 182 GHz channel to sense the strong vertical moisture gradient below 700 mb, at the bottom edge of the upper level frontal zone. / Source: Dissertation Abstracts International, Volume: 55-01, Section: B, page: 0131. / Major Professor: Henry E. Fuelberg. / Thesis (Ph.D.)--The Florida State University, 1993.

An EOF methodology is applied to a hemispheric two-layer, baroclinic, primitive equation model to better understand the advantages and drawbacks of EOF modeling in numerical prediction. A spectral transform version of the model (truncated at T31) is integrated to generate a 100 year "nature" run. EOFs, from that run, are analyzed and used as basis functions in a simplified version of the model. By employing the EOFs as basis functions in the dynamical model, we obtain a system of quadratic nonlinear equations involving the EOF coefficients. / A statistical analysis is based on the spectral domain EOF expansion of the streamfunction, velocity potential and thickness of each layer. A comparison with spatially and temporally uncorrelated noise suggests that the first 65 PCs (6.4% of the total number of degrees of freedom) are significant and provide for a relatively good resolution of the individual modes; These account for about 96% of variance. / The predictability of the EOF model is examined when the number of EOF modes is truncated at 50, 100 and 150. A set of 1800 experiments of EOF model forecasts were run with different initial conditions for each EOF truncation. The root mean square error and anomaly correlation are used as measures of predictability. It was found that, at short-range, the forecast skill improves as the number of EOF modes retained in the model increases. For example, an EOF model truncated at 150 improves the average anomaly correlation of 3 day forecasts from 0.63 to 0.73 when compared with the model truncated at 50. However, there is a cross-over point (at about 6 days) after which the low resolution EOF model out-performs the high resolution EOF model in predicting the dominant modes. A similar result holds when the high resolution model is the nature run and initial errors are sufficiently large. This points to a potentially important application of truncated EOF models to extended-range forecasting. It remains to be seem, however, whether in applications to the atmosphere, the advantage of neglecting unresolved/uncertain scales in predicting the dominant modes occurs at a point when forecast skill is still useful. / Source: Dissertation Abstracts International, Volume: 55-04, Section: B, page: 1349. / Major Professor: Albert Barcilon. / Thesis (Ph.D.)--The Florida State University, 1994.

A method is developed to initialize convective storm simulations with Doppler radar-derived fields. Input fields for initialization include velocity, rain water derived from radar reflectivity, and pressure and temperature fields obtained through thermodynamic retrieval. A procedure has been developed to fill in missing wind data, followed by a variational adjustment to the filled wind field to minimize "shocks" that would otherwise cause the simulated fields to deteriorate rapidly. / A series of experiments using data from a simulated storm establishes the feasibility of the initialization method. Multiple Doppler radar observations from the 20 May 1977 Del City tornadic storm are used for the initialization experiments. Simulation results initialized from observations taken at two different stages of storm development are shown and compared to observations taken at later times. A simulation initialized from one of the observation times showed good agreement with subsequent observations, though the simulated storm appeared to be evolving much faster than observed. Possible mechanisms for error growth are discussed. / Source: Dissertation Abstracts International, Volume: 53-10, Section: B, page: 5251. / Major Professor: Peter S. Ray. / Thesis (Ph.D.)--The Florida State University, 1992.

A simple but realistic parameterization of ground wetness is developed and implemented in the FSUGSM to model in climate. Specifically, a soil moisture parameter based on a moisture budget, is introduced to estimate the Bowen ratio. It is expressed as an evolutive function of the model predicted rainfall, surface temperature and takes into account ground characteristics through its dependence on albedo and surface elevation. This scheme is used in conjunction with a prognostic equation for surface temperature to determine the surface fluxes. / A global spectral model is used to perform two parallel forecasts, one of which includes the new scheme. Monthly situations for selected variables are presented. Comparison of the components of the surface energy balance are carried out for different types of climatic regime over Africa during summer. / The new scheme captures the essence of the known physics in simple formulation of the processes and introduced interesting modulation of the fluxes. Reduction of the surface temperature and its diurnal cycle is observed. This is particularly evident over arid zones. / An important and coherent interaction between the physical processes has resulted from the introduction of the scheme and led to better representation of the distribution of the heat sources at the surface. / Realistic rainfall rates and distribution are obtained over the Sahelian region. / Significant improvement has been introduced in the prediction of primary variables near the surface. The effect of the new land surface processes parameterization was, however, not clearly discernible in the upper level model atmosphere structure. / Source: Dissertation Abstracts International, Volume: 53-10, Section: B, page: 5251. / Major Professor: T. N. Krishnamurti. / Thesis (Ph.D.)--The Florida State University, 1992.

A two-dimensional, nonlinear, time-dependent, non-hydrostatic, anelastic, numerical model is used to assess the effect of condensation on the evolution and structure of gravity waves generated by the passage of a stable, moist stream over topography. Precipitation is ignored but water phase changes are taken into account explicitly. / The numerical approach uses centered finite differences, except for liquid water, which is advected by using an upwind scheme. A constant basic wind and a constant stability are assumed in order to isolate the effects of moisture. At the inflow boundary the wind velocity is kept constant with time, whereas at the outflow boundary, the Orlanski (1976) extrapolation scheme is applied. Spurious reflections from the upper boundary are minimized by an absoring (sponge) layer. As initial conditions we impose an irrotational flow and zero buoyancy, consistent with the physics of impulsively started motions. / Evolution for hydrostatic and non-hydrostatic flows have been studied. For both, the wave field, immediately after the start-up, consists of a V-shaped pattern, similar to that obtained experimentally by Mowbray and Rarity (1967). As time progresses, only the upwind branch of the pattern remains, with new waves piling up above the mountain peak in the hydrostatic case; or forming a stack above and downwind from the mountain peak in the non-hydrostatic case. In both cases, the inclusion of moisture steepens the pattern. / The main effect of condensation is to damp the wave intensity and to reduce the wave drag, which can be diminished by as much as 50% compared to its value in dry simulations. / A breaking wave case has been also studied. It has been found that the presence of condensation delays the overturning of isentropes and the formation of the critical layer that accompanies wave-breaking. / Source: Dissertation Abstracts International, Volume: 45-02, Section: B, page: 0586. / Thesis (Ph.D.)--The Florida State University, 1984.

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.