Approved for public release, distribution is unlimited / This thesis investigated the hypothesis that variations in tropical cyclone (TC) activity in the western North Pacific (WNP) may affect the teleconnection between the tropical WNP and North America. The teleconnection patterns of the 500 hPa geopotential height between a base point in the WNP (20 N 115 E) and a domain over North America (30 - 45 N, 70 -90 W) from 1951-2001 were examined. The 25 most active and the 25 least active TC years for two regions with the highest climatological average of TC activity, near the Philippines and Taiwan, respectively, were compared to determine if stronger teleconnection patterns occur during the more active years. For both regions, the correlation pattern is significant during active years and insignificant during inactive years, with the results based on TC activity in the Philippines region showing a larger difference. An analysis of 500 hPa mean winds showed weaker winds in the midlatitudes during active TC years when the teleconnection is stronger, which suggests that the teleconnection may consist mainly of Lau and Weng's (2000) zonally-elongated mode (Mode 1). Further cross correlations of the geopotential height and TC frequency parameters with the tropical eastern and western Pacific sea-surface temperatures (SST's) showed a significant correlation between TC activity and tropical eastern Pacific SST's, but the North America-WNP correlation is unlikely to be a result of a direct influence of SST's on the two regions. / Captain, United States Air Force

When a tropical cyclone (TC) is within 360 nautical miles of Kadena AB, the Air Force's Typhoon Determination (TYDET) program is used to estimate TC-induced winds expected at the base. Best-track data and Joint Typhoon Warning Center (JTWC) forecasts are used to evaluate systematic errors in TYDET. The largest contributors to errors in TYDET are a systematic error by which wind speeds are too large and the lack of size and symmetry parameters. To examine these parameters, best-track and forecasts are used to classify TCs as small or large and symmetric or asymmetric. A linear regression technique is then used to adjust TYDET forecasts based on the best-track and forecast position, size, and symmetry categories. Using independent data, over 65 percent of the overall cross-wind forecasts were improved and more than 60 percent of the cross-wind forecasts were improved when verifying conditions noted a cross-wind of 20 knots or greater. The effectiveness of the corrections and implications for TYDET forecasts are examined in relation to errors in forecast data used to initialize TYDET. A similar approach as developed here for the TYDET model at Kadena AB is proposed for other bases within the Pacific theater.

The Niuean population has been in decline since the airport opened on the island. This thesis investigates a specific aspect of the migration from the island: what final year high school students in Niue plans to do after graduation in relation to leaving or staying in Niue. The study relates this decision to place attachment, values and climate change.The study indicates that Niuean youth doesn’t want to study on the island but instead move to New Zealand to pursue their academic ambitions. The students exhibit a strong sense of place attachment that is based in their identification with the island culture and nature. They want to return to the island after getting their university degree, making them attached stayers. The risk of cyclones does not affect the students wishes to live on the island. Decisions are in large motivated by caring for family, the students want to get a degree and then return to be able to take care and give back to their parents, grandparents and other people that have cared for them during their childhood.

Sampling of airborne dust in industry is influenced by the potential health effects associated with human exposure. Health effects depend on mass concentration and particle size which influences the site of pulmonary deposition. Occupational diseases tend to be associated with dust deposition in specific regions of the respiratory tract. The ACGIH size selective TLVs are expressed in three forms: Inhalable Particulate Matter, Thoracic Particulate Matter, and Respirable Particulate Matter. In pneuomoconioses, the amount of dust deposited in the lungs can be estimated by sampling the respirable fraction. Dose-response relationships are derived by relating the health experience of workers to the extent of their exposure to respirable dust. It can be readily seen that validity of these relationships depends primarily on the accuracy of estimation of the exposure dose. Different sampling techniques, such as impactors, horizontal elutriators and cyclones were used for decades to estimate the exposure to respirable dusts. Cyclones have been the most widely utilized. However, the performance curve of the cyclone is considerably different from observed dust deposition data in the human alveolar compartment. Current methods of measuring respirable dust overestimate that dust fraction, which results in underestimating the agent’s toxicity in dose-response relationships. In this investigation, a new concept for sampling respirable dust was proposed and validated. The goal of this study was to design a combined impactor/cyclone device that provides better estimation of the amount of respirable dust. The objectives of this study were: 1) to calibrate ten single-stage impactors previously deigned and machined by Dr. Hammad, 2) to obtain the collection efficiency curves of ten impactor-cyclone combinations by superimposing the collection efficiency curves of impactors on the well-defined cyclone efficiency curve, and 3) to compare the combined efficiency curves to actual human alveolar deposition data, and thus validate this new concept for sampling of respirable dust. The experiment was conducted in a 20’’x20’’x20’’ aerosol testing chamber constructed from aluminum with a glass window. A LoveLace nebulizer with a nominal droplet size of 7 micrometers was used to generate fluorescent monodisperse polystyrene latex aerosols 0.5, 1, 2, and 3 micrometers in diameter. A Vilnius aerosol generator was used to generate fluorescent PSL dry powders 6 micrometers in diameter. The generated aerosols were collected on 37 mm polyvinyl chloride filters positioned after the impactors. Sample fluorescence was determined using a GloMax-Multi Jr fluorometer. Impactor efficiencies at the various sizes were used to construct the collection curves of impactors. Efficiency curves were subsequently superimposed on the cyclone efficiency curve to obtain the final efficiencies of the sampling devices. The results indicated that the cut-off diameters increased with impactor jet size. The new efficiency curves of the sampling devices had similar shapes to actual alveolar deposition as determined experimentally in human subjects. Actually they fell between actual alveolar deposition curves 2 and 4 seconds for mean residence times. The findings from this work can be applied to design a novel respirable dust sampler that provides a realistic estimate of pulmonary deposition to be used in dose- response relationships for the various mineral dusts encountered in general and mining industries. The under estimation of the dust toxicity associated with the current sampling methodology may be one of the reasons for continuous lowering of the TLV and PEL for silica.

Abstract not available

Although a tropical cyclone may conceptually be regarded as an axisymmetric vortex, there is substantial evidence that asymmetric dynamics play an important role. In this thesis, dynamical impacts of rotating convective asymmetries are examined in this thesis. Two types of rotating convective asymmetries are considered: rotating eyewall convective maximum which is located in the core region of the storm and spiral bands which are located outside the core. Both of them can be characterized as rotating asymmetric convective heat sources, and they are superimposed on a balanced, axisymmetric vortex to approximate the effect of rotating eyewall convective maximum and spiral bands on tropical cyclone by using a simple nonhydrostatic three-dimensional, but linear model that is based on vortex anelastic equations. The evolution of rotating convective asymmetric heat sources on a balanced, axisymmetric vortex, which is modeled after tropical cyclones, is investigated to examine angular momentum transport by gravity waves that radiate away from the core region. Results show that gravity waves can transport angular momentum away from a tropical cyclone, but a very small amount, which is several orders of magnitude smaller than the estimate by recent studies. The significantly large difference may largely be due to the difference between two-dimensional and three-dimensional adjustment processes. Assuming that the effects of spiral bands on tropical cyclone wind field are caused by the response to diabatic heating in their convection, rotating asymmetric heat sources are constructed to reflect observations of spiral bands. These heat sources are rotated around a realistic but idealized balanced axisymmetric vortex. Simulation results show that the response of tropical cyclone wind field to idealized spiral band heat sources can successfully capture a number of observed well-known features of spiral band circulation, such as overturning secondary circulation, descending mid-level inflow, and cyclonic tangential acceleration. Comparison to full-physics numerical simulations confirms the validity of this method which provides a simple dynamical framework to better understand the impact of spiral bands in tropical cyclone.

The ocean mixed layer response to a tropical cyclone within, and immediately adjacent to, the Gulf of Mexico Loop Current is examined using a combination of ocean profiles and a numerical model. A comprehensive set of temperature, salinity, and current profiles acquired from aircraft-deployed expendable probes is utilized to analyze the three-dimensional oceanic energy and circulation evolution in response to Hurricane Lili's (2002) passage. Mixed-layer temperature analyses show that the Loop Current cooled <1 degree C in response to the storm, in contrast to typically observed larger decreases of 3-5 degrees C. Correspondingly, vertical current shears, which are partly responsible for entrainment mixing, were found to be up to 50% weaker, on average, than observed in previous studies within the directly-forced region. The Loop Current, which separates the warmer, lighter Caribbean Subtropical water from the cooler, heavier Gulf Common water, was found to decrease in intensity by -0.18 plus/minus 0.25 m/s over an approximately 10-day period within the mixed layer. Contrary to previous tropical cyclone ocean response studies which have assumed approximately horizontally homogeneous ocean strucutre prior to storm passage, a kinetic energy loss of 5.8 plus/minus 6.3 kJ/m^2, or approximately -1 wind stress-scaled energy unit, was observed. Using near-surface currents derived from satellite alimetery data, the Loop Current is found to vary similarly in magnitude, suggesting storm-generated energy is rapidly removed by the pre-exiting Loop Current. Further examination of the energy response using an idealized numerical model reveal that due to: 1) favorable coupling between the wind stress and pre-existing current vectors; and 2) wind-driven currents flowing across the large horizontal pressure gradient; wind energy transfer to mixed-layer kinetic energy can be more efficient in these regimes as compared to the case of an initially horizontally homogeneous ocean. However, nearly all of this energy is removed by advection by 2 local inertial periods after storm passage, and little evidence of the storm's impact remains. Mixed-layer vorticity within the idealized current also shows a strong direct response, but little evidence of an near-inertial wave wake results.

Cette thèse se penche sur différents aspects des cyclones tropicaux tels que simulés par des modèles de circulation générale (MCG) et un modèle régional de climat (MRC), le modèle régional de climat canadien (MRCC5). D'abord, nous évaluons la capacité d'un ensemble de MCG, utilisé dans le cadre du 4e rapport du GIEC (Groupe d'experts Intergouvernemental sur l'Évolution du Climat), à capturer les principales zones de cyclogenèse au travers d'indices dérivés à partir des champs atmosphériques favorables à la formation des cyclones tropicaux. En comparant les événements de cyclogenèse observés avec les deux indices calculés à partir de réanalyses et d'un ensemble de MCG, nous vérifions que les indices arrivent à relativement bien représenter la distribution actuelle des cyclones tropicaux, autant dans les modèles que les réanalyses. En comparant des simulations couvrant la période 2080-2100 avec la période présente, l'indice jugé plus stable projette une légère augmentation du nombre des tempêtes dans le Pacifique Ouest. Le deuxième partie de la thèse est consacrée à évaluer la capacité du MRCC5 à reproduire la climatologie des cyclones tropicaux observée durant la période 1979-2006. Plus précisément, nous évaluons l'impact d'une augmentation de la résolution sur les caractéristiques physiques des cyclones ainsi que sur leur distribution géographique, de même que l'impact des conditions aux frontières, de la technique de « downscaling » dynamique utilisée et de la taille du domaine sur les cyclones simulés. Une telle évaluation est une étape cruciale à toute étude d'impact des changements climatiques sur les ouragans. La distribution des cyclones est consistante avec la distribution d'un indice de cyclogenèse, ce qui permet de mieux comprendre les changements observés dans les différentes simulations. Aussi, nous évaluons la capacité du modèle à reproduire la variabilité interannuelle observée durant cette période, et plus particulièrement l'impact de l'oscillation australe d'El Niño (El Niño Southern Oscillation ou ENSO) sur la cyclogenèse. Finalement, nous étudions les ondes d'Est africaines, systèmes précurseurs des ouragans dans l'Atlantique, tel que simulées par le MRCC5 de même que leur relation avec les cyclones tropicaux de l'Atlantique. Règle générale, le MRCC5 arrive à reproduire de façon réaliste l'activité observée durant la période 1979-2006. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : cyclones tropicaux, indices de cyclogenèse, ondes d'Est africaines, modèle régional de climat, modèle de circulation générale

This study was concerned with the most common reverse flow type of cyclones where the flow enters the cyclone through a tangential inlet and leaves via an axial outlet pipe at the top of the cyclone. Numerical computations of two different cyclones were based on the so-called Stairmand cyclone. The difference in geometry between these two cyclones was basically characterized by the geometrical swirl number Sg of 3.5 and 4. Turbulent secondary flows inside a straight square channel have been studied numerically by using Large Eddy Simulation (LES) in order to verify the implementation process. Prandtl’s secondary motion calculated by LES shows satisfying agreement with both, Direct Numerical Simulation (DNS) and experimental results. Numerical calculations were carried out at various axial positions and at the apex cone of a gas cyclone separator. Two different NS-solvers (a commercial one, and a research code), based on a pressure correction algorithm of the SIMPLE method have been applied to predict the flow behavior. The flow was assumed as unsteady, incompressible and isothermal. A k − epsilon turbulence model has been applied first using the commercial code to investigate the gas flow. Due to the nature of cyclone flows, which exhibit highly curved streamlines and anisotropic turbulence, advanced turbulence models such as RSM (Reynolds Stress Model) and LES (Large Eddy Simulation) have been used as well. The RSM simulation was performed using the commercial package CFX4.4, while for the LES calculations the research code MISTRAL/PartFlow-3D code developed in our multiphase research group has been applied utilizing the Smagorinsky model. It was found that the k − epsilon model cannot predict flow phenomena inside the cyclone properly due to the strong curvature of the streamlines. The RSM results are comparable with LES results in the area of the apex cone plane. However, the application of the LES reveals qualitative agreement with the experimental data, but requires higher computer capacity and longer running times than RSM. These calculations of the continuous phase flow were the basis for modeling the behavior of the solid particles in the cyclone separator. Particle trajectories, pressure drop and the cyclone separation efficiency have been studied in some detail. This thesis is organized into five chapters. After an introduction and overview, chapter 2 deals with continuous phase flow turbulence modeling including the governing equations. The emphasis will be based on LES modelling. Furthermore, the disperse phase motion is treated in chapter 3. In chapter 4, the validation process of LES implementation with channel flow is presented. Moreover, prediction profiles of the gas flow are presented and discussed. In addition, disperse phase flow results are presented and discussed such as particle trajectories; pressure drop and cyclone separation efficiency are also discussed. Chapter 5 summarizes and concludes the thesis.

Thesis (Ph. D.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references (leaves 181-193).