Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Meteorology, 1979. / Microfiche copy available in Archives and Science. / Bibliography: leaves 86-88. / by Dawna Lisa Paton. / M.S.

As ondas de calor constituem sequências extremas de elevadas temperaturas que podem causar prejuízos biológicos, econômicos e sociais, desta forma demandando discussões em planejamentos estratégicos para a manutenção do funcionamento social. No entanto, inexistem trabalhos que as abordem historicamente em suas complexidades estatísticas, sinóticas e termodinâmicas em toda a extensão da América do Sul (AS), sendo os estudos ora restritivos no tempo, ora restritivos no espaço. Esta dissertação identifica e analisa as ondas de calor sobre a AS em suas distintas áreas de atuação regional, para um período de 30 anos, fazendo uso dos dados diários de reanálise do European Centre for Medium-Range Weather Forecasts (ECMWF), com resolução de 0,75° na área delimitadas pelas coordenadas (60°S15°N) e (8530°W). Para isto adota um critério de identificação objetivo e consistente com a variabilidade da extensão temporal e da intensidade das anomalias positivas de temperaturas, discutindo os aspectos metodológicos não consensuais presentes na literatura. As ondas de calor foram agrupadas segundo os padrões de variabilidade guiados por fenômenos atmosféricos específicos, em uma nova técnica alternativa ao uso das Funções Ortogonais Empíricas, derivada dos mapas de correlações espaciais. Os resultados mostram que as ondas de calor acontecem em qualquer época do ano, preferencialmente no período climatológico de maiores temperaturas; além disso, sua frequência está aumentando com o passar dos anos na AS. Para completar, os mapas de composições das climatologias sinóticas permitem identificar sistemas meteorológicos específicos para cada uma das dez regiões homogêneas identificadas, alguns deles relacionados ao fenômeno El Niño Oscilação-Sul e a padrões determinados de circulação atmosférica, precipitação e Temperatura da Superfície do Mar. Tendo em vista a possibilidade de inclusão da mesma técnica aos estudos globais e para as ondas de frio, este trabalho se insere no início de uma vasta gama de estudos inter-relacionados, dentro do contexto das mudanças climáticas e de considerável interesse socioeconômico envolvido. / Heat waves constitute extreme sequences of high temperatures that can cause biological, economic, and social damages, thus requiring strategic planning discussion for social functioning maintenance. However, there are no papers addressing them from a historical point of view in their statistical, synoptic, and thermodynamic complexities throughout South America (SA), being the studies sometimes restrictive in time, and sometimes restrictive in space. This dissertation identifies and analyses the SA heat waves over their regional areas, for a period of 30 years, making use of reanalysis daily data of European Centre for Medium-Range Weather Forecasts (ECMWF), with 0.75° resolution over the area delimited by the coordinates ranges (60°S15°N) and (8530°W). To do that, it adopts an objective identification criterion consistent with the variability of the temporal extension and the intensity of the positive anomalies of temperatures, discussing the nonconsensual methodological aspects present in the literature. The heat waves were grouped according to the variability patterns guided by specific atmospheric phenomena, in a new alternative technique to the use of the Empirical Orthogonal Functions, derived from the maps of spatial correlations. The results show that the heat waves happen at any time of the year, preferably in the climatic period of higher temperatures; in addition, its frequency is increasing over the years in AS. To complete, the correlation maps of synoptic climatology allow the identification of specific meteorological systems in each of the ten identified homogeneous region, some of them related with El Niño Southern Oscillation and with determined patterns of atmospheric circulation, precipitation, and Sea Surface Temperature. Considering the possibility of including the same technique in global studies and in the case of cold waves, this work is part of a wide range of interrelated studies within the context of climate change and considerable socioeconomic interest involved.

As ondas de calor constituem sequências extremas de elevadas temperaturas que podem causar prejuízos biológicos, econômicos e sociais, desta forma demandando discussões em planejamentos estratégicos para a manutenção do funcionamento social. No entanto, inexistem trabalhos que as abordem historicamente em suas complexidades estatísticas, sinóticas e termodinâmicas em toda a extensão da América do Sul (AS), sendo os estudos ora restritivos no tempo, ora restritivos no espaço. Esta dissertação identifica e analisa as ondas de calor sobre a AS em suas distintas áreas de atuação regional, para um período de 30 anos, fazendo uso dos dados diários de reanálise do European Centre for Medium-Range Weather Forecasts (ECMWF), com resolução de 0,75° na área delimitadas pelas coordenadas (60°S15°N) e (8530°W). Para isto adota um critério de identificação objetivo e consistente com a variabilidade da extensão temporal e da intensidade das anomalias positivas de temperaturas, discutindo os aspectos metodológicos não consensuais presentes na literatura. As ondas de calor foram agrupadas segundo os padrões de variabilidade guiados por fenômenos atmosféricos específicos, em uma nova técnica alternativa ao uso das Funções Ortogonais Empíricas, derivada dos mapas de correlações espaciais. Os resultados mostram que as ondas de calor acontecem em qualquer época do ano, preferencialmente no período climatológico de maiores temperaturas; além disso, sua frequência está aumentando com o passar dos anos na AS. Para completar, os mapas de composições das climatologias sinóticas permitem identificar sistemas meteorológicos específicos para cada uma das dez regiões homogêneas identificadas, alguns deles relacionados ao fenômeno El Niño Oscilação-Sul e a padrões determinados de circulação atmosférica, precipitação e Temperatura da Superfície do Mar. Tendo em vista a possibilidade de inclusão da mesma técnica aos estudos globais e para as ondas de frio, este trabalho se insere no início de uma vasta gama de estudos inter-relacionados, dentro do contexto das mudanças climáticas e de considerável interesse socioeconômico envolvido. / Heat waves constitute extreme sequences of high temperatures that can cause biological, economic, and social damages, thus requiring strategic planning discussion for social functioning maintenance. However, there are no papers addressing them from a historical point of view in their statistical, synoptic, and thermodynamic complexities throughout South America (SA), being the studies sometimes restrictive in time, and sometimes restrictive in space. This dissertation identifies and analyses the SA heat waves over their regional areas, for a period of 30 years, making use of reanalysis daily data of European Centre for Medium-Range Weather Forecasts (ECMWF), with 0.75° resolution over the area delimited by the coordinates ranges (60°S15°N) and (8530°W). To do that, it adopts an objective identification criterion consistent with the variability of the temporal extension and the intensity of the positive anomalies of temperatures, discussing the nonconsensual methodological aspects present in the literature. The heat waves were grouped according to the variability patterns guided by specific atmospheric phenomena, in a new alternative technique to the use of the Empirical Orthogonal Functions, derived from the maps of spatial correlations. The results show that the heat waves happen at any time of the year, preferably in the climatic period of higher temperatures; in addition, its frequency is increasing over the years in AS. To complete, the correlation maps of synoptic climatology allow the identification of specific meteorological systems in each of the ten identified homogeneous region, some of them related with El Niño Southern Oscillation and with determined patterns of atmospheric circulation, precipitation, and Sea Surface Temperature. Considering the possibility of including the same technique in global studies and in the case of cold waves, this work is part of a wide range of interrelated studies within the context of climate change and considerable socioeconomic interest involved.

A time dependent model of the shallow, tropical convective boundary layer is developed and tested. To simplify the treatment of thermodynamic processes and return to first principles of physics, conserved quantities of entropy and total water density are used as primary model variables. In addition, a new shallow cumulus parameterization scheme is developed and is based on the use of a time dependent cloud kinetic energy equation combining local concepts of cloud processes with the use of a special buoyancy length scale. Two model simulations are performed in an attempt to assess the model's performance and the effectiveness of the parameterization scheme. Results indicate that the model does a reasonable job in both representing the equilibrium structure of a shallow convective boundary layer and in generating a realistic boundary layer structure from an initial state consisting of a shallow moist layer with dry air aloft. The cumulus parameterization scheme appears to adequately represent the transport of thermodynamic quantities associated with convective activity and the use of conserved variables provides an effective way of representing the boundary layer structure and treating the mixing processes associated with cloud processes. This work illustrates the usefulness of generalized conserved variables, particularly entropy and total water density, and indicates that the general approach of using a time dependent cloud kinetic energy equation may be effective for representing thermodynamic processes in the tropical boundary layer. / Graduation date: 1992

This thesis aims to improve the understanding of transport and critical layer mixing in the troposphere and stratosphere. A dynamical approach is taken based on potential vorticity which has long been recognised as the essential field inducing the flow and thermodynamic structure of the atmosphere. Within the dynamical framework of critical layer mixing of potential vorticity, three main topics are addressed. First, an idealised model of critical layer mixing in the stratospheric surf zone is examined. The effect of the shear across the critical layer on the critical layer evolution itself is investigated. In particular it is found that at small shear barotropic instability occurs and the mixing efficiency of the critical layer increases due to the instability. The effect of finite deformation length is also considered which extends previous work. Secondly, the dynamical coupling between the stratosphere and troposphere is examined by considering the effect of direct perturbations to stratospheric potential vorticity on the evolution of midlatitude baroclinic instability. Both zonally symmetric and asymmetric perturbations to the stratospheric potential vorticity are considered, the former representative of a strong polar vortex, the latter representative of the stratospheric state following a major sudden warming. A comparison of these perturbations gives some insight into the possible influence of pre or post-sudden warming conditions on the tropospheric evolution. Finally, the influence of the stratospheric potential vorticity distribution on lateral mixing and transport into and out of the tropical pipe, the low latitude ascending branch of the Brewer-Dobson circulation, is investigated. The stratospheric potential vorticity distribution in the tropical stratosphere is found to have a clear pattern according to the phase of the quasi-biennial oscillation (QBO). The extent of the QBO influence is quantified, by analysing trajectories of Lagrangian particles using an online trajectory code recently implemented in the Met Office's Unified Model.

Tempestades severas ocorrem na Região Metropolitana de São Paulo (RMSP) principalmente nos meses quentes e úmidos do ano. Nesta tese, os mecanismos de disparo da convecção profunda são estudados por meio de análises observacionais e simulações numéricas com o Advanced Regional Prediction System (ARPS). A metodologia proposta compreende o uso da parametrização microfísica fria na simulação dos processos físicos que levam à formação de nuvens cumulonimbus, sem o uso da parametrização de cúmulos nas grades de altíssima resolução espacial. Nos eventos estudados, as primeiras células de precipitação observadas e simuladas surgiram em razão da interação entre o escoamento atmosférico na camada limite planetária e a topografia local. As células secundárias foram geralmente mais intensas, uma vez que elas surgiram após o aquecimento diabático adicional. O mecanismo de disparo das células secundárias foi a corrente ascendente induzida pela propagação horizontal das frentes de rajada em baixos níveis da atmosfera das correntes descendentes das células primárias. As frentes de rajada tiveram velocidade de propagação horizontal típica de 6 m s-1. No evento de 02 de fevereiro de 2004, células convectivas profundas foram simuladas com alto grau de realismo no domínio da grade de 3 km de resolução espacial. Observou-se que, neste caso, a frente de brisa marítima pôde atuar como guia de ondas para a colisão entre duas frentes de rajada. A propagação da frente de brisa marítima para o interior do continente ocorreu em conjunção a um forte gradiente de vapor dágua nos níveis mais baixos da troposfera. As células convectivas profundas secundárias surgiram e se desenvolveram exatamente nesta zona de interface, a qual representa o contraste entre as diferentes massas de ar marítima e continental. No evento de 04 de fevereiro de 2004, na grade de 1 km de resolução, a análise objetiva com as medidas das estações de superfície na RMSP correspondente às 1800 UTC indicou a presença de uma ilha de calor urbana com até 4 oC de aquecimento diferencial entre a Capital e vizinhanças. O principal efeito da assimilação destas medidas foi a redução do NCL em até 80 hPa, o que favoreceu o disparo da convecção naquela área. / Severe thunderstorms occur in the Metropolitan Area of São Paulo (MASP) mainly in the warm and wet months of the year. In this work, the triggering mechanisms of deep convection are studied through observed data and numerical simulations with the Advanced Regional Prediction System (ARPS). The proposed methodology focuses in the use of microphysics parameterization of cold clouds to simulate physical process linked to the life cycle of thunderstorms. The cumulus cloud parameterization isnt used in high resolution numerical grids. In the real case studies, both observed and simulated, early convective cells developed as a consequence of the interaction between the planetary boundary layer atmospheric flow and the local topography. The secondary convective cells were generally strongest, once they developed after additional surface diabatic heating. The triggering mechanism of these secondary cells was the updraft induced by gust fronts generated by downdrafts of primary cells. The gust fronts had a typical horizontal propagation velocity of 6 m s-1. In the February 02 2004 event, deep convective cells were simulated with high degree of realism with a 3 km resolution grid. It was observed that, in this case, the sea-breeze front could act as a wave guide to the collision between two different gust fronts. In addition, the sea breeze front propagated to the continental area together with a strong low level water vapor gradient. The secondary deep convective cells arose and developed exactly on this interface zone, which represents the contrast between the oceanic and continental air masses. The interface zone was marked by a water vapor mixing rate of 14 g kg-1. In the February 04 2004 event, the objective analysis, made with some MASP´s surface stations measurements at 1800 UTC in the 1 km resolution grid, indicates the presence of an urban heat island with up to 4 oC of differential heating between São Paulo city and its neighboring area. The main effect in assimilating these surface measurements was the lowering of the lift condensation level up to 80 hPa, which favored the triggering of convection in that area.

Tempestades severas ocorrem na Região Metropolitana de São Paulo (RMSP) principalmente nos meses quentes e úmidos do ano. Nesta tese, os mecanismos de disparo da convecção profunda são estudados por meio de análises observacionais e simulações numéricas com o Advanced Regional Prediction System (ARPS). A metodologia proposta compreende o uso da parametrização microfísica fria na simulação dos processos físicos que levam à formação de nuvens cumulonimbus, sem o uso da parametrização de cúmulos nas grades de altíssima resolução espacial. Nos eventos estudados, as primeiras células de precipitação observadas e simuladas surgiram em razão da interação entre o escoamento atmosférico na camada limite planetária e a topografia local. As células secundárias foram geralmente mais intensas, uma vez que elas surgiram após o aquecimento diabático adicional. O mecanismo de disparo das células secundárias foi a corrente ascendente induzida pela propagação horizontal das frentes de rajada em baixos níveis da atmosfera das correntes descendentes das células primárias. As frentes de rajada tiveram velocidade de propagação horizontal típica de 6 m s-1. No evento de 02 de fevereiro de 2004, células convectivas profundas foram simuladas com alto grau de realismo no domínio da grade de 3 km de resolução espacial. Observou-se que, neste caso, a frente de brisa marítima pôde atuar como guia de ondas para a colisão entre duas frentes de rajada. A propagação da frente de brisa marítima para o interior do continente ocorreu em conjunção a um forte gradiente de vapor dágua nos níveis mais baixos da troposfera. As células convectivas profundas secundárias surgiram e se desenvolveram exatamente nesta zona de interface, a qual representa o contraste entre as diferentes massas de ar marítima e continental. No evento de 04 de fevereiro de 2004, na grade de 1 km de resolução, a análise objetiva com as medidas das estações de superfície na RMSP correspondente às 1800 UTC indicou a presença de uma ilha de calor urbana com até 4 oC de aquecimento diferencial entre a Capital e vizinhanças. O principal efeito da assimilação destas medidas foi a redução do NCL em até 80 hPa, o que favoreceu o disparo da convecção naquela área. / Severe thunderstorms occur in the Metropolitan Area of São Paulo (MASP) mainly in the warm and wet months of the year. In this work, the triggering mechanisms of deep convection are studied through observed data and numerical simulations with the Advanced Regional Prediction System (ARPS). The proposed methodology focuses in the use of microphysics parameterization of cold clouds to simulate physical process linked to the life cycle of thunderstorms. The cumulus cloud parameterization isnt used in high resolution numerical grids. In the real case studies, both observed and simulated, early convective cells developed as a consequence of the interaction between the planetary boundary layer atmospheric flow and the local topography. The secondary convective cells were generally strongest, once they developed after additional surface diabatic heating. The triggering mechanism of these secondary cells was the updraft induced by gust fronts generated by downdrafts of primary cells. The gust fronts had a typical horizontal propagation velocity of 6 m s-1. In the February 02 2004 event, deep convective cells were simulated with high degree of realism with a 3 km resolution grid. It was observed that, in this case, the sea-breeze front could act as a wave guide to the collision between two different gust fronts. In addition, the sea breeze front propagated to the continental area together with a strong low level water vapor gradient. The secondary deep convective cells arose and developed exactly on this interface zone, which represents the contrast between the oceanic and continental air masses. The interface zone was marked by a water vapor mixing rate of 14 g kg-1. In the February 04 2004 event, the objective analysis, made with some MASP´s surface stations measurements at 1800 UTC in the 1 km resolution grid, indicates the presence of an urban heat island with up to 4 oC of differential heating between São Paulo city and its neighboring area. The main effect in assimilating these surface measurements was the lowering of the lift condensation level up to 80 hPa, which favored the triggering of convection in that area.

M.Phil. (Energy Studies) / Southern Africa is a major source of regional aerosols and trace gases from biomass burning, and this creates a need for experimental validation and systematics of the magnitude and frequency of aerosol transport episodes affecting the atmosphere of the region. This study links surface measurements of biomass burning atmospheric aerosols and trace gases with air mass trajectory analysis to determine transport pathways for periods of high and low concentrations. The hypothesis of this study is that from chemical signatures of trace gases and aerosols, as well as trajectory analyses, it is possible to identify sources of these emissions from industrial, traffic, marine and biomass burning activities. Consequently, frequencies, durations, intensities and seasonal variations of trace gases can be established. The study aims to interpret the long-term atmospheric monitoring record from a remote monitoring station at Botsalano (North West Province, South Africa) to determine the origin, frequencies, durations, intensities and seasonal occurrences of aerosol/haze episodes influencing the atmosphere of southern Africa. A suite of trace gas analysers and a Differential Mobility Particle Sizer (DMPS®) were used to measure ground level trace gas and aerosol quantities. MATLAB® scripts were used in performing quality assurance and processing to provide a working set of data from which different fire periods could be selected. Fire signatures, based on excess CO above average tropospheric levels and episodes of enhanced particulate matter concentrations in the 10 to 200 nm range, were identified using MATLAB® scripts and Excel®. Altogether 36 plumes were accepted as biomass burning plumes. Twenty-nine fire plumes had weak signals with excess CO ratios ranging between 0.07 and 0.32; seven plumes had strong signals ranging between 0.41 and 0.64. The occurrence of identified biomass burning plumes was high in the dry season from May to October (83%) and low (17%) during the wet season from November to April. Four pathways were identified for the long-range transportation of biomass burning aerosols to the site: easterly, south-westerly, re-circulation and northerly modes, with occurrence frequencies of 39%, 31%, 22% and 8%, respectively. Anti-cyclonic circulation was observed over southern Africa and was evident in the re-circulation and Indian Ocean slow modes. CO and Aitken-mode aerosol number intensities were generally larger for fire emissions arriving in the easterly and south-westerly air masses when compared with those arriving in re-circulation and northerly air masses. Easterly and south-westerly flows were dominated by Aitken-mode aerosol, whereas accumulation mode particles dominated in the re-circulation and northerly modes. Consequently, easterly and south-westerly flows transported emissions from young/fresh fire plumes, with source regions probably close to Botsalano. Re-circulation and northerly flows were responsible for transport of rather aged plumes from more distant regional fires. Based on forward trajectories, this study revealed that the 2006/2007 measurement period exhibited transport features of a La Niña ENSO during which transport of biomass v burning aerosols towards the south in the Indian Ocean slow and Indian Ocean fast modes was most frequent. This study is significant in that it complements earlier studies of regional aerosol transport over the sub-continent and adds to the understanding of the regional scale generation and transport of trace substances through the atmosphere. Furthermore, the study combines a technique for identifying enhanced CO concentrations as a unique identifier of large scale biomass combustion events with the use of the Aitken-mode particle number densities and size distributions. This technique reveals aspects of aerosol growth dynamics through the changing size distributions, thereby adding fresh insights normally not available through conventional particle volume/mass concentrations measurements.

Les abondances atmosphériques du dioxyde de carbone et du méthane augmentent progressivement, modifiant probablement le climat global de l'atmosphère. Bien que ces effets soient très étudiés dans la troposphère, ils le sont peu dans l'atmosphère moyenne (20 - 120 km) où ils pourraient avoir un impact plus facilement détectable. Nous nous intéressons en particulier à la mésosphère/basse thermosphère (MLT), où apparaissent de plus en plus souvent des nuages mésosphériques polaires (PMC). La MLT est sensible au niveau d'activité solaire, qui varie selon un cycle de onze ans.<p>Nous évaluons les impacts de ces deux changements anthropiques et de ce cycle naturel sur la température et la chimie de la MLT. Pour ce faire, nous participons au développement d'un modèle bidimensionnel de l'atmosphère :SOCRATES. Ce modèle calcule interactivement les moyennes zonales des vents, de la température et de la composition chimique de l'atmosphère en fonction de la latitude (85°S-85°N) et de l'altitude (0-120 km). Avant de nous intéresser au changement global, nous avons dû améliorer SOCRATES pour qu'il reproduise au mieux la situation chimique, dynamique et thermique actuellement observée.<p>Nous avons ainsi modifié la résolution du système chimique; développé une nouvelle paramétrisation de l'absorption par O2 du rayonnement solaire ultraviolet à Lyman-&61537; (121.6 nm) [Chabrillat et Kockarts, 1997] ;créé une approximation des sources thermosphériques de NO; paramétrisé le forçage dynamique par déferlement des ondes de gravité pour reproduire de manière très réaliste les observations actuelles de température dans la MLT ;et développé un algorithme pour prendre en compte non seulement la diffusion turbulente mais aussi la diffusion moléculaire. Tous ces développements sont décrits en détail, et leurs effets sur la physico-chimie de la. MLT sont analysés. Les concentrations chimiques calculées par le modèle sont comparées avec succès à des observations - en particulier de l'ozone et du radical hydroxyle.<p>Nous étudions ensuite en détail l'impact du cycle solaire de onze ans sur la MLT. Une analyse complète du budget thermique nous permet d'établir, par exemple, que la raie Lyman-&61537; est responsable de la moitié du réchauffement entre SOLMIN et SOLMAX. Nous évaluons alors la sensibilité de la MLT à un doublement (théorique) de l'abondance de C02. Nous trouvons qu'aux hautes latitudes et en été, zone d'apparition des PMC, cet effet est très faible. Puis nous réalisons une simulation où le méthane est ramené à son niveau préindustriel. L'accroissement de CH4 depuis cette époque est responsable, non seulement de l'augmentation de la vapeur d'eau dans l'atmosphère moyenne, mais aussi d'un léger refroidissement dans la MLT. Cet effet est maximal dans les régions polaires et en été, là où les deux autres sont minimaux.<p>Nous concluons par une grande simulation intégrée de l'évolution du climat et de la chimie de l'atmosphère moyenne au cours du XXIe siècle. Nous trouvons qu'au niveau d'apparition des PMC, la tendance au refroidissement est plus faible que partout ailleurs. Par contre, la vapeur d'eau augmente plus rapidement en été qu'en hiver. Ces calculs fournissent des indices pour réconcilier les observations plus fréquentes des PMC avec une synthèse des températures mesurées dans l'été arctique, selon laquelle les températures n'auraient pas varié depuis quarante ans.<p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished