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model-derived wind gusts determined by each method are then compared to wind reports from the Storm Prediction Centerâ s severe storm reports archive and reports from observing stations. Model-derived wind gusts are then compared to the observed wind gusts for varying times of day and observed wind gust ranges. Wind gust frequency plots are examined for each wind method to determine accuracy and to characterize any patterns. The T1 method was the most accurate overall for this study, but was shown to be less sensitive to varying atmospheric conditions. The T2 method was the least accurate of the three methods during all situations. The WINDEX method performed well in most situations and was nearly as accurate as the T1 method, while WINDEX also proved to be the most sensitive of the three to varying mesoscale conditions.

A three-dimensional mechanistic model of the middle atmosphere is used to model various classes of equatorial wave motions that are observed in the atmosphere. These waves are thought to be largely responsible for the forcing of the quasi-biennial oscillation (QBO) in the tropical lower stratosphere. By generating a combination of different classes of equatorial waves in the model, an oscillation which has many similarities to the observed QBO is produced in the model. The numerical model used is run in a variety of configurations, including running it at different vertical resolutions and with two different radiation parameterisation schemes. It is found that model used in the project must be modified to allow the accurate modelling of equatorial waves. Several modelling problems are encountered while applying the modifications necessary in the model; the steps necessary to rectify these problems are detailed in this thesis. Equatorial waves are then forced in this modified model under a range of conditions and their interaction with the mean flow is observed. Their dissipation mechanisms and the influence of changes in model conditions on these waves are investigated. The model is found to be generally very successful in modelling these equatorial waves. Modelling of the QBO is one of the principle aims of this project and a QBO is successfully generated in a variety of model configurations. The modelled QBO is found to be sensitive to changes in the temperature structure of the model (brought about by changes in the model's radiation scheme) and several experiments are performed in order to learn what processes affect this sensitivity. A QBO is then generated in series of model runs where the state of the model is varied from very idealised (where temperatures in the model are relaxed towards an isothermal state by the radiation scheme) to a state that is far more realistic (a perpetual January run with realistic boundary information). A fairly realistic QBO is generated throughout many of the experiments. The properties of this QBO are investigated and compared to the observed QBO. The model is then run with planetary waves forced in addition to the QBO. The interaction between the planetary waves and the QBO is investigated. It is found that the planetary waves have little effect on the QBO propagation. The QBO however has a fairly strong modulating effect on the planetary waves in certain regions.

This thesis describes an experimental technique for measuring the atomic-oxygen concentration under simulated upper atmosphere conditions.

The gas phase reactions of atomic chlorine with hydrogen sulfide, ammonia, benzene, and ethylene are investigated using the laser flash photolysis / resonance fluorescence experimental technique. In addition, the kinetics of the reverse processes for the latter two elementary reactions are also studied experimentally. The absolute rate constants for these processes are measured over a wide range of conditions, and the results offer new accurate information about the reactivity and thermochemistry of these systems. The temperature dependences of these reactions are interpreted via the Arrhenius equation, which yields significantly negative activation energies for the reaction of the chlorine atom and hydrogen sulfide as well as for that between the phenyl radical and hydrogen chloride. Positive activation energies which are smaller than the overall endothermicity are measured for the reactions between atomic chlorine with ammonia and ethylene, which suggests that the reverse processes for these reactions also possess negative activation energies. The enthalpies of formation of the phenyl and β-chlorovinyl are assessed via the third-law method. The stability and reactivity of each reaction system is further rationalized based on potential energy surfaces, computed with high-level ab initio quantum mechanical methods and refined through the inclusion of effects which arise from the special theory of relativity. Large amounts of spin-contamination are found to result in inaccurate computed thermochemistry for the phenyl and ethyl radicals. A reformulation of the computational approach to incorporate spin-restricted reference wavefunctions yields computed thermochemistry in good accord with experiment. The computed potential energy surfaces rationalize the observed negative temperature dependences in terms of a chemical activation mechanism, and the possibility that an energized adduct may contribute to product formation is investigated via RRKM theory.

Ein neues Schema für die Parametrisierung der Schwerewellen und ihres Einflusses auf die mittlere Atmosphäre ist für COMMA-LIM (COlogne Model of the Middle Atmosphere - Leipzig Institute for Meteorology) übernommen worden. Während das bisher in COMMA-LIM genutzte aktualisierte Lindzen-Schema (Lindzen, 1981) die Ausbreitung und das Brechen einzelner Wellen berechnet, geht das Warner und McIntyre-Schema von einem Spektrum der Schwerewellen aus. Beide Schemata gehen von Schwerewellen im mittleren Frequenzbereich zwischen Brunt-Väisäla Frequenz und Rotationsrate der Erde aus (N >> ω >> f). Erste Ergebnisse werden vorgestellt. / A new scheme for the parametrizing of the gravity waves and their impact on the mean circulation of the middle atmosphere has been adapted to COMMA-LIM (COlogne Model of the Middle Atmosphere - Leipzig Institute for Meteorology). The current version based on the Lindzen-scheme (Lindzen, 1981) calculates the propagation and breaking of 48 single waves while the new Warner and McIntyre - scheme uses a spectral approach of gravity waves. Both schemes are based on the medium frequency approach locating the gravity waves between the Brunt-Väisälä-frequency and the rotation rate of the earth ((N >> ω >> f). First results are presented.

The uncertainty in the determination of the momentum and scalar fluxes remains one of the main obstacles to accurate numerical forecasts in low to moderate wind conditions. For example, latent heat fluxes computed from data using direct covariance and bulk aerodynamic methods show that there is good agreement in unstable conditions when the latent heat flux values are generally positive. However, the agreement is relatively poor in stable conditions, particularly when the moisture flux is directed downward. If the direct covariance measurements are indeed accurate, then they clearly indicate that the bulk aerodynamic formula overestimate the downward moisture flux in stable conditions. As a result, comparisons of the Dalton number for unstable and stable conditions indicate a marked difference in value between the two stability regimes. Investigations done for this thesis used data taken primarily at the Air-Sea Interaction Tower (ASIT) during the Coupled Boundary Layers and Air-Sea Transfer (CBLAST) Experiment 2003 from the 20-27 August 2003. Other data from the shore based Martha's Vineyard Coastal Observatory (MVCO) and moored buoys in the vicinity of the ASIT were also incorporated. During this eight day period, the boundary layer was often characterized by light winds, a stably stratified surface layer and a swell dominated wave field. Additionally, the advection of warm moist air over cooler water resulted in fog formation and a downward flux of moisture on at least three occasions. Therefore, a primary objective of this thesis is to present a case study to investigate the cause of this shortcoming in the bulk formula under these conditions by examining the physical processes that are unique to these boundary layers. Particular attention will be paid to the behavior of the Dalton number in a stable marine atmospheric boundary layer under foggy conditions using insights derived from the study of fog formation and current flux parameterization methods.

Orientador: Raquel Fernandes Pupo Nogueira / Coorientador: Maria Lúcia Arruda de Moura Campos / Banca: Lilian Rothschild / Banca: Adalgiza Fornaro / Resumo: A chuva é um mecanismo fundamental para a remoção de substâncias da atmosfera, cuja análise pode trazer informações importantes sobre a composição química da baixa troposfera local-regional. Neste trabalho, amostras de água de chuva foram coletadas no Instituto de Química de Araraquara, de janeiro de 2008 a dezembro de 2012. A determinação de carbono orgânico dissolvido (COD) e carbono orgânico não purgável (CONP) foi feita pelo analisador de carbono e a quantificação de AA e FA por derivatização com a solução ácida 2,4-DNPH, em que as respectivas hidrazonas formadas foram determinadas por cromatografia líquida de alta eficiência (CLAE) com detecção em 360 nm. O pH apresentou uma média ponderada pelo volume (MPV) de 5,6 (n= 107) e uma boa correlação com o íon Ca2+ (r= 0,5809), indicando que a ressuspensão do solo pode ter contribuído para neutralizar parte da acidez. A MPV das concentrações de K+ e Ca2+ foi de 3,9 (n= 106) e 4,8 (n= 105) μmol L-1, respectivamente, sendo que a concentração de K+ apresentou variação sazonal, com um aumento no período de safra da cana-deaçúcar, indicando a sua importante fonte na queima de biomassa. A MPV de COD (n= 118) encontrada em Araraquara foi de 263 ± 30 μmol L-1 sendo superior no período de safra da cana-de-açúcar (314 ± 46 μmol L-1; n= 74) do que no período de entressafra (182 ± 24 μmol L-1; n= 44). As concentrações de COD em Araraquara apresentaram correlações lineares significativas com K+ (0,8098) e com Ca2+ (0,6972), indicando que a queima de biomassa e a ressuspensão do solo são importantes fontes de emissão de carbono orgânico para a atmosfera. As concentrações de COD foram sempre superiores nos primeiros milímetros de chuva quando comparadas com o evento completo. Porém, o COD teve uma queda menos... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The rain is a fundamental mechanism for the removal of substances from the atmosphere, which analysis can provide important information on the local-regional composition. In this work, samples of rainwater were collected at the Institute of Chemistry of Araraquara, from January 2008 to December 2012. Determination of dissolved organic carbon (DOC) and non purgeable organic carbon (NPOC) was made by carbon analyzer and AA and FA were quantified after derivatization with acid solution of 2,4-DNPH, where the respective hydrazones formed were determined by high performance liquid chromatography (HPLC) with detection at 360 nm wavelength. The pH presented a volume weighted average (VWA) of 5.6 (n= 107) and presented significant correlation with Ca2+ (r = 0.5809) indicating that soil resuspension may have contributed to neutralization of part of the acidity. The VWA of K+ and Ca2+ concentration was 3.9 (n = 106) and 4.8 (n = 105) μmol L-1, respectively,and the concentration of K+ showed seasonal variation, with an increase during the period of sugarcane harvest, indicating its major source in biomass burning. The MPV DOC (n = 118) found in Araraquara was 263 ± 30 μmol L-1 being higher during the harvest of sugar cane (314 ± 46 μmol L-1, n = 74) than in nonharvest period (182 ± 24 μmol L-1, n = 44). The concentrations of DOC in Araraquara showed significant linear correlations with K+ (0.8098) and Ca2+ (0.6972), indicating that biomass burning and soil resuspension are important sources of organic carbon to the atmosphere. DOC concentrations were always higher in the first millimeters of rain in comparison with the entire event. However, the DOC had a less steep decrease, indicating that these species are removed from the atmosphere by the process of below cloud and in cloud. The percentage... (Complete abstract click electronic access below) / Mestre

Thesis (MTech (Chemistry))--Cape Peninsula University of Technology, 2017. / The purpose of the present study was to apply data collected monthly over a 6-year period along the almost 200 km long St. Helena Bay Monitoring Line in the Southern Benguela upwelling system to investigate co-variation between an upwelling index calculated from nearby wind records and physical and chemical properties along the transect. The extent to which the well-documented seasonal upwelling cycles is manifested at the surface along an inshore-offshore variation was investigated in the context of implications for the validity of remote sensing as a monitoring tool in this ocean area and to improve understanding of the physical drivers of biological processes in St. Helena Bay. This study shows that surface temperature and nutrient concentrations exhibit very poor seasonality and weak correlation with the upwelling index. This is, despite clear evidence for spatial inshore-offshore gradients in temperature, nutrients, and chlorophyll-a, consistent with an upwelling regime. The upper ocean temperature gradient shows a much better correspondence to the upwelling index but at the same time demonstrates that surface heating, and not vertical mixing related to upwelling, controls the upper ocean temperature gradient. In this study linear lagged correlations were also examined and discussed to gain insight into the effect upwelling has on the surface waters in St. Helena Bay with the view of determining the following: (1) Does upwelling lead to an increase or decrease of the water properties? (2) What is the characteristic lag between an upwelling event and its effect on these water properties? (3) Is the effect and/or lag different for the different seasons? and (4) Is the effect and/or lag different for stations inside the bay and those outside the bay?. A combination of surface turbulent cooling through upwelling occurred after a lag of 8 to 10 days in winter and early summer, but less than half in late summer, similar to results obtained with salinity. However, the rest of the salinity results fit in poorly with the temperature results. The only significant correlation obtained with the inshore stations during late summer is the inexplicable positive correlation at a lag of 7 days. For all three seasons virtually none of the oxygen results fit the expected pattern. All three nutrients showed a more positive correlation coefficient and significance than the negative ones. Significant negative correlations occurred mainly during late summer at lags of 7 to 9 days caused by planktonic depletion of nutrients. Also, in this season, significant positive correlations between south-north wind and nutrients only occurred at short lags. This observation supports the earlier temperature-based conclusion that the influence of upwelling develops most rapidly at this time of the year. A rapid increase in chlorophyll-a levels followed by nutrient enrichment of the surface layers are evident. iii The results suggest that remote sensing techniques would be inadequate tools to monitor upwelling events in the Southern Benguela. Secondly, the incidence of phytoplankton blooms is more likely triggered by stratified conditions associated with surface heating than relaxation of upwelling winds. Finally, these results also emphasise the importance of validating lagged outputs against real-time measurements in supporting a simpler hydrological model in narrowing down these significant uncertainties.

This thesis presents the results from investigations into various features of the dynamics of the middle atmosphere. Wind measurements from the meteor radar on Ascension Island and temperatures measured by the Aura MLS instrument are used to characterise Ultra-Fast Kelvin Waves (UFKW) in the MLT-region. Rainfall rates from TRMM are used as a proxy for latent heat release in an investigation of the excitation of UFKW, and results are compared with predictions of the Kyushu-GCM. Amplitudes and vertical wavelengths are determined, as are the accelerations resulting from wave dissipation. Intra-seasonal oscillations (ISOs) are observed in the wave amplitudes and accelerations, and oscillations with the same periods are observed in the rainfall and MLT-region winds, suggesting that UFKW play a role in carrying the tropospheric ISOs to higher regions. The seasonal and interannual variability of the tidal field over Ascension Island is investigated. Amplitudes, phases and vertical wavelengths of the diurnal and semidiurnal tides are reported on. Our observations of tidal parameters are compared with the predictions of the extended Canadian Middle Atmosphere Model (eCMAM) and the Whole Atmosphere Community Climate Model (WACCM). Correlations between tidal amplitudes, the stratospheric Quasi-Biennial Oscillation (QBO) and the El Nin ̃o Southern Oscillation (ENSO) are discussed. The Hocking (2005) method is adapted to recover monthly-mean gravity-wave momentum fluxes and wind variances either side of the Drake passage gravity-wave hotspot. The ability of the method to recover momentum fluxes over each radar are tested by sampling a series of specified (known) wave fields of increasing complexity with the actual meteor distributions, and comparing the recovered momentum fluxes with the specified values. The analysis is then applied to the real data to obtain climatologies of the MLT-region variances and momentum fluxes for a composite year of the 2008 to 2012 data.