Nuvens desempenham um papel fundamental no balanço radiativo terrestre, e o conhecimento de suas propriedades micro e macrofísicas é importante para o estudo do clima global. O desenvolvimento convectivo de nuvens está intimamente relacionado ao comportamento microfísico de seus hidrometeoros, os quais são influenciados pela variação nas concentrações de aerossóis disponíveis na atmosfera. Este trabalho utiliza o sensoriamento remoto por satélites para analisar a evolução diurna de propriedades ópticas de hidrometeoros de nuvens sobre a Amazônia. Para tanto, medidas de radiância efetuadas pelos canais 1, 2 e 4 do satélite geoestacionário GOES 13 para os anos de 2012, 2013, 2014 e 2015 foram aliadas a códigos computacionais de transferência radiativa visando a obtenção de estimativas de raios efetivos de gotas e partículas de gelo em nuvens convectivas. A variação temporal de parâmetros microfísicos ao longo do dia foi analisada durante as estações seca e úmida em dois locais prístinos e outros dois locais significativamente atingidos pela fumaça de queimadas na Amazônia. A profundidade óptica de aerossóis ( a em 550 nm) variou de 0,1 a 0,2 na maior parte do ano (estação úmida) sobre todos os locais. Na estação seca nos sítios prístinos observou-se um a em torno de 0,5 unidades, e de cerca de 0,8 nos sítios degradados. Os resultados mostram que para todos os locais analisados há 32% mais pixels de nuvens durante a estação úmida do que na seca. As distribuições relativas de refletâncias em 0,63 m e da temperatura de brilho em 11 m indicam que em todos os sítios e épocas do ano há predominância de nuvens menos espessas e mais quentes sobre a Amazônia. A análise da refletância em 3,90 m indicou que nos quatro locais ocorre uma redução do raio efetivo de hidrometeoros de nuvens quentes na estação seca em relação à estação úmida. A distribuição de raios efetivos é bimodal para todos os sítios e estações analisados, sendo a variação diurna dessa distribuição consistente com processos de desenvolvimento vertical de nuvens e crescimento de hidrometeoros. Esse mecanismo ocorre de maneira distinta em locais mais e menos poluídos, sendo que para regiões mais poluídas e desmatadas o desenvolvimento vertical de tamanhos de partículas na época seca se dá de maneira mais lenta do que na úmida. Para as áreas mais atingidas pela pluma de fumaça durante a estação seca os raios efetivos de gotas/cristais de gelo com temperatura de brilho maior que -20°C praticamente não mudam, sofrendo uma variação máxima de 2 m num período de 2 horas. Para o mesmo intervalo de temperaturas e de tempo a estação seca em ambientes mais limpos apresenta uma variação de até 6 m nos raios efetivos das partículas. Esse resultado é parcialmente compatível com modelos conceituais que procuram explicar efeitos microfísicos de aerossóis sobre o tamanho de hidrometeoros em nuvens. O atraso no crescimento vertical de hidrometeoros é mais pronunciado perto do meio dia solar e em locais onde as concentrações de aerossóis provenientes de queimadas são maiores. / Clouds play a key role in Earths radiative balance. The knowledge of its micro and macrophysical properties is important for the study of global climate. The life cycle of convective clouds is closely related to the microphysics of its hydrometeors, which are influenced by many factors including variations in the concentration of atmospheric aerosols. This study uses remote sensing by a satellite to analyze the diurnal evolution of reflective properties of clouds over Amazon. Radiance measurements performed by channels 1, 2 and 4 of the imager instrument onboard GOES-13 geostationary satellite, from 2012 to 2015, were analyzed using radiative transfer and computational codes. This allowed deriving estimates of the effective radius of cloud droplets and ice particles in convective clouds. The temporal variation of microphysical parameters throughout the day was analyzed during the dry and wet seasons at two pristine sites and two other sites significantly affected by biomass burning smoke in the Amazon. The aerosol optical depth ( a at 550 nm) ranged from 0.1 to 0.2 for most of the year (wet season) over all sites. In the dry season at the pristine sites a a of about 0.5 units was observed, while about 0.8 units were measured at the degraded sites. The results show that for all analyzed sites there were 32% more cloudy pixels during the wet season than in the dry season. The relative distribution of reflectance at 0.63 m and the brightness temperature at 11 m indicate that at all sites and times of the year there is a predominance of shallow warm clouds in the Amazon. The analysis of the reflectance at 3.90 m indicated that at the four sites a reduction of the effective radius of hydrometeors in warm clouds occurs in the dry season in comparison to the wet season. The distribution of effective radius is bimodal for all sites and seasons. The diurnal variation of this bimodal distribution is consistent with processes of vertical cloud development and hydrometeor growth. This mechanism occurs differently in the pristine and degraded sites. At polluted and deforested regions the vertical development of particle sizes in the dry season occurs more slowly than in pristine ones. For the areas more affected by smoke plumes during the dry season the effective radius of drops/ice crystals of clouds with brightness temperature greater than -20°C show small changes with height, undergoing a maximum variation of 2 m in 2 hours. For the same temperature range and time interval in the dry season, clouds in cleaner environments showed a variation up to 6 m in the effective radius of particles. This result is partly compatible with conceptual models that seek to explain microphysical effects of aerosols on the size of hydrometeors. The vertical growth delay of hydrometeors is more pronounced near local solar noon and in places where the concentration of smoke aerosols is higher.

Este trabalho procura mostrar como a mulher ortodoxa judia é representada no cinema israelense. A partir da análise de três filmes: Kadosh, de Amos Gitai, produzido em 1999; Hasodot (Segredos Íntimos), de Avi Nesher, produzido em 2007 e Chufshat Kaitz (My Father, my Lord), de David Volach, produzido em 2007, busca-se compreender como se deram os processos culturais que determinaram alguns comportamentos da sociedade ortodoxa judaica em relação à mulher, enfocando os seguintes temas: fertilidade feminina, homossexualidade, a educação das mulheres e o silêncio. Como arcabouço teórico central estão as obras Vigiar e punir e A microfísica do poder, de Michel Foucault e as fontes tradicionais judaicas, como o Talmud, a Bíblia Hebraica, e outros textos canônicos, utilizadas no sentido de entender como o conhecimento se transforma em poder dentro da sociedade ortodoxa judaica e, nesse contexto, como a mulher é sujeitada por ele. / This paper seeks to show how the orthodox jewish woman is represented in Israeli cinema. From the analysis of three films: Kadosh by Amos Gitai, produced in 1999; Hasodot (The Secrets) by Avi Nesher, produced in 2007 and Chufshat Kaitz (My Father, My Lord) by David Volach, produced in 2007, we look to understand how cultural processes have led to some behaviors of the orthodox jewish community facing women, focusing on the following topics: female fertility, homosexuality, women\'s education and silence. Central theoretical framework are the works by Michel Foucault: Discipline and Punish and The microphysics of power, and the traditional Jewish sources, as the Talmud, the Hebrew Bible, and other canonical texts, used in order to understand how knowledge is transformed into power within the orthodox jewish society and in this context, as the woman is subjected by it.

A detailed understanding of cloud microphysical processes is crucial for a large range of scientific disciplines that require knowledge of cloud particles for accurate climate and weather prediction. This thesis focuses on 3 measurement campaigns, encompassing both airborne and ground based measurements of the microphysical structures observed in cold, warm and occluded frontal systems around the United Kingdom, stratocumulus clouds in the Arctic and many different clouds observed over a 6 week period at a high-alpine site in the Swiss Alps. Particular attention was paid to the origin and distribution of both primary and secondary ice and the dominant features associated with ice phase processes. During investigation of cold, warm and occluded frontal systems associated with mid-latitude cyclones around the U.K., secondary ice was often found to dominate the number and mass concentrations of ice particles in all systems. The presence of large liquid droplets was sometimes observed in close proximity to regions of secondary ice production. The existence of these provides a possible mechanism by which rime-splintering is greatly enhanced through the creation of instant rimers as the large drops freeze. In-situ measurements during the cold frontal case were used to calculate rates of diabatic heating during a comparison between bin-resolved and bulk microphysics schemes. Observations in arctic stratocumulus clouds during spring and summer seasons revealed higher ice concentrations in the summer cases when compared to the spring season. This is attributed to secondary ice production actively enhancing ice concentrations in the summer, due to the higher temperature range the clouds spanned. At Jungfraujoch in the Swiss Alps, ground based measurements allowed us to obtain high spatial scale resolution measurements of cloud microphysics and we found transitions between high and low ice mass fractions that took place on differing temporal scales spanning seconds to hours. During the campaign measurements of aerosol properties at an out of cloud site, Schilthorn, were made. When analysing a Saharan Dust Event that took place a possible link between the number of U.V. fluorescent particles and the number of ice particles was found in the temperature range around -10 ºC.

La météorologie tropicale est un élément majeur pour le fonctionnement de l’atmosphère et pour le climat terrestre. Le satellite Megha-Tropiques regroupe des instruments de télédétection utilisant des algorithmes de restitution complexes. Cette thèse participe à la mise au point de stratégies de validation de ces algorithmes par l’acquisition d’une meilleure connaissance de la phase glacée des systèmes convectifs de méso-échelle (MCS) tropicaux, en s’appuyant sur la campagne de mesures réalisée à Niamey au Niger à l’été 2010. De nombreux MCS à fort contenu en glace (IWC, Ice Water Content) ont été documentés à la fois par une instrumentation aéroportée, et par des radars au sol. Les informations obtenues grâce aux sondes aéroportées, et l’utilisation d’une loi masse-diamètre permettent de calculer une valeur de réflectivité Zin-situ. Le développement d’une méthode de colocalisation des mesures réalisées par les radars sol sur la trajectoire de l’avion a abouti à la validation du calcul de Zin-situ. La relation entre la réflectivité et l’IWC n’a pas été clairement observée pour le radar-précipitation du MIT. De plus, l’IWC est mieux documenté avec un radar-nuage qu’avec un radar-précipitation car ce dernier est trop sensible aux cristaux de grande taille. Les mesures in-situ s’avèrent donc indispensables pour obtenir l’information microphysique utile à la validation des algorithmes de restitution satellites et elles ne peuvent pas être remplacées par des mesures de réflectivités effectuées depuis le sol. L’utilisation du modèle numérique WRF (Weather Research and Forecasting) pourrait également permettre de connaître au mieux les MCS. Pour le cas d’étude analysé dans cette thèse, la modélisation a généré une ligne de grains mais n’a pas reproduit correctement toutes les caractéristiques du MCS réellement observé. Des différences dynamiques et microphysiques sont apparues. L’analyse du champ de réflectivité simulé grâce aux CFAD (Contoured Frequency by Altitude Diagrams) a montré une sous-estimation de la réflectivité par rapport aux observations. L’utilisation du schéma microphysique de Morrison, plus complexe que celui de Thompson initialement employé, n’a pas permis d’améliorer les résultats. Les performances du modèle WRF ne sont pas encore suffisantes pour aider à la validation des algorithmes de restitution satellites. / Tropical meteorology is a major issue for atmospheric physics and earth’s climate. The Megha-Tropiques satellite combines several teledetection instruments which need complex restitution algorithms. This work contributes to the development of validation’s strategies for these algorithms. This requires a better knowledge of the tropical mesoscale convective systems’ (MCS) ice phase. In this thesis, we use data from the Niamey’s (Niger) campaign, which took place during summer 2010. Numerous MCS with high Ice Water Content (IWC) were analyzed with an airborne instrumentation and ground radars. Reflectivity Zin-situ is calculated using airborne microphysic probes’ information and a mass-diameter relationship. A spatial and temporal interpolation technique is developed to colocalize the aircraft position with ground radar measurements. This method leads to the validation of Zin-situ calculation. The relationship between reflectivity and IWC is not satisfactory for the MIT precipitation radar. Moreover, the cloud radar gives better informations about the IWC than the precipitation radar. Indeed, precipitation radars are too sensitive to large ice crystals. Therefore, in-situ measurements are essential to get microphysic information in order to validate restitution algorithms used by satellites. They can’t be replaced by ground based reflectivity measurements. The WRF (Weather Research and Forecasting) model was used in order to get a better knowledge of MCS. In this work, we analyzed one case study. For this case, WRF generates a typical squall line but it doesn’t correctly reproduce every observed characteristics. Several dynamical and microphysical differences appear between simulation and observations. The simulated reflectivity field is analyzed by CFAD (Contoured Frequency by Altitude Diagrams) and it shows a general underestimated reflectivity compared to the observations. The Thompson microphysic scheme is replaced by the more complex Morrison scheme, but this modification doesn’t improve the results of the simulation. Consequently, the WRF model isn’t yet efficient enough to help with the restitution algorithms’ validation.

The Second Aerosol Characterization Experiment (ACE-2) data set along with ECMWF reanalysis meteorological fields provided the basis for the single column model (SCM) simulations, performed as part of the PACE (Parameterization of the Aerosol Indirect Climatic Effect) project. Six different SCMs were used to simulate ACE-2 case studies of clean and polluted cloudy boundary layers, with the objective being to identify limitations of the aerosol/cloud/radiation interaction schemes within the range of uncertainty in in situ, reanalysis and satellite retrieved data. The exercise proceeds in three steps. First, SCMs are configured with the same fine vertical resolution as the ACE-2 in situ data base to evaluate the numerical schemes for prediction of aerosol activation, radiative transfer and precipitation formation. Second, the same test is performed at the coarser vertical resolution of GCMs to evaluate its impact on the performance of the parameterizations. Finally, SCMs are run for a 24–48 hr period to examine predictions of boundary layer clouds when initialized with large-scale meteorological fields. Several schemes were tested for the prediction of cloud droplet number concentration (N). Physically based activation schemes using vertical velocity show noticeable discrepancies compared to empirical schemes due to biases in the diagnosed cloud base vertical velocity. Prognostic schemes exhibit a larger variability than the diagnostic ones, due to a coupling between aerosol activation and drizzle scavenging in the calculation of N. When SCMs are initialized at a fine vertical resolution with locally observed vertical profiles of liquid water, predicted optical properties are comparable to observations. Predictions however degrade at coarser vertical resolution and are more sensitive to the mean liquid water path than to its spatial heterogeneity. Predicted precipitation fluxes are severely underestimated and improve when accounting for sub-grid liquid water variability. Results from the 24–48 hr runs suggest that most models have problems in simulating boundary layer cloud morphology, since the large-scale initialization fields do not accurately reproduce observed meteorological conditions. As a result, models significantly overestimate optical properties. Improved cloud morphologies were obtained for models with subgrid inversions and subgrid cloud thickness schemes. This may be a result of representing subgrid scale effects though we do not rule out the possibility that better large-forcing data may also improve cloud morphology predictions.

With a nearly twice as strongly pronounced temperature increase compared to that of the Northern Hemisphere, the Arctic is especially susceptible to global climate change. The effect of clouds on the Arctic warming is especially uncertain, which is caused by misrepresented cloud microphysical processes in atmospheric models. This thesis aims at employing a scale- and definition-aware comparison of models and observations and will propose changes how to better parameterize Arctic clouds in atmospheric models. In the first part of this thesis, ECHAM6, which is the atmospheric component of the MPI-ESM global climate model, is compared to spaceborne lidar observations of clouds from the CALIPSO satellite. This comparison shows that ECHAM6 overestimates Arctic low-level, liquid containing clouds over snow- and ice-covered surfaces, which consequently leads to an overestimated amount of radiative energy received by the surface. Using sensitivity studies, it is shown that the probable cause of the model biases in cloud amount and phase is related to misrepresented cloud microphysical parameterization (i.e., parameterization of the Wegener-Bergeron-Findeisen process and of the cloud cover scheme) in ECHAM6. By revising those processes, a better representation of cloud amount and cloud phase is achieved, which helps to more accurately simulated the amount of radiative energy received by the Arctic in ECHAM6. The second part of this thesis will focus on a comparison of kilometer-scale simulation with the ICON model to aircraft observations from the ACLOUD campaign that took place in May/June 2017 over the sea ice-covered Arctic Ocean north of Svalbard, Norway. By comparing measurements of solar and terrestrial surface irradiances during ACLOUD flights to the respective quantities in ICON, it is shown that the model systematically overestimates the transmissivity of the mostly liquid clouds during the campaign. This model bias is traced back to the way cloud condensation nuclei get activated into cloud droplets in the two-moment, bulk microphysical scheme used. By parameterizing subgrid-scale vertical motion as a function of turbulent kinetic energy, a more realistic CCN activation into cloud droplets is achieved. This consequently results in an improved representation of cloud optical properties in the ICON simulations. Furthermore, the results of two studies to which contributions have been made during the Ph.D. will be summarized. In Petersik et al. 2018, the impact of subgrid-scale variability in clear-sky relative humidity on hygroscopic growth of aerosols in the aerosol-climate model ECHAM6-HAM2 has been explored. It was shown that the revised parameterization of hygroscopic growth of aerosols resulted in a stronger swelling of aerosol particles, which consequently causes an increased backscattering of solar radiation. In the study of Costa-Suros et al. 2019, it is explored whether it is possible to detect and attribute aerosol-cloud interactions in large-eddy simulation over Germany. It was shown that an increase in cloud droplet number concentration could be attributed to an increased aerosol load, while such an attribution was not possible for other cloud micro- and macrophysical variables.

We propose a mathematical procedure to derive a stochastic parameterization for the bulk warm cloud micro-physical properties of collision and coalescence. Unlike previous bulk parameterizations, the stochastic parameterization does not assume any particular droplet size distribution, all parameters have physical meanings which are recoverable from data, all equations are independently derived making conservation of mass intrinsic, the auto conversion parameter is finely controllable, and the resultant parameterization has the flexibility to utilize a variety of collision kernels. This new approach to modelling the kinetic collection equation (KCE) decouples the choice of a droplet size distribution and a collision kernel from a cloud microphysical parameterization employed by the governing climate model. In essence, a climate model utilizing this new parameterization of cloud microphysics could have different distributions and different kernels in different climate model cells, yet employ a single parameterization scheme. This stochastic bulk model is validated theoretically and empirically against an existing bulk model that contains a simple enough (toy) collision kernel such that the KCE can be solved analytically. Theoretically, the stochastic model reproduces all the terms of each equation in the existing model and precisely reproduces the power law dependence for all of the evolving cloud properties. Empirically, values of stochastic parameters can be chosen graphically which will precisely reproduce the coefficients of the existing model, save for some ad-hoc non-dimensional time functions. Furthermore values of stochastic parameters are chosen graphically. The values selected for the stochastic parameters effect the conversion rate of mass cloud to rain. This conversion rate is compared against (i) an existing bulk model, and (ii) a detailed solution that is used as a benchmark. The utility of the stochastic bulk model is extended to include hydrodynamic and turbulent collision kernels for both clean and polluted clouds. The validation and extension compares the time required to convert 50\% of cloud mass to rain mass, compares the mean rain radius at that time, and used detailed simulations as benchmarks. Stochastic parameters can be chosen graphically to replicate the 50\% conversion time in all cases. The curves showing the evolution of mass conversion that are generated by the stochastic model with realistic kernels do not match corresponding benchmark curves at all times during the evolution for constant parameter values. The degree to which the benchmark curves represent ground truth, i.e. atmospheric observations, is unknown. Finally, among alternate methods of acquiring parameter values, getting a set of sequential values for a single parameter has a stronger physical foundation than getting one value per parameter, and a stochastic simulation is preferable to a higher order detailed method due to the presence of bias in the latter. / Graduate / 0725 0608 0405 / davidc@uvic.ca

Le littoral méditerranéen français est fréquemment affecté en automne par des épisodes de forte pluie. La région montagneuse des Cévennes – Vivarais (Massif Central) est une des régions affectées par ces épisodes de précipitations intenses (appelés Cévenols) qui peuvent provoquer des catastrophes naturelles entraînant des dommages économiques importants et des pertes de vies humaines. La prévision de tels épisodes par les modèles numériques de prévision du temps a été considérablement améliorée; cependant, des incertitudes en ce qui concerne leur intensité demeurent. L’amélioration des paramétrisations microphysiques dans ces modèles de prévision est un élément clé pour la réduction des erreurs. Le but de cette étude était de mieux comprendre les processus microphysiques qui régissent les épisodes de fortes précipitations et l’impact des particules d’aérosol atmosphériques sur ces précipitations en exploitant les observations du programme de recherche HYMEX et de la campagne de mesures associée qui s’est déroulée en 2012 dans le Sud de la France. L’étude s’est portée sur l’épisode de précipitation intense observé le 26 Sept. 2012 lors de la Période d’Observations Intenses (POI) 7a. Les observations disponibles ont été évaluées et comparées aux résultats de simulations effectuées avec le DEtailed SCAvenging Model (DESCAM, Flossmann and Wobrock; 2010) qui est un modèle tridimensionnelle utilisant un schéma bin pour représenter de manière détaillée la microphysique nuageuse ainsi que les interactions entre les particules d’aérosols et les nuages. Les observations utilisées ont été faites à partir d'instruments au sol et des mesures aéroportées in situ et permettent d'évaluer le modèle. Les observations au sol sont issues de radars en bande X, de Micro-Rain Radars (MRR), de disdromètres, mais également d’une réanalyse statistique des mesures de pluie par pluviomètres et radars opérationnels (Boudevillain et al. 2016). Les observations aéroportées in-situ ont été réalisées à l’aide de sondes microphysiques et du radar nuage RASTA embarqués à bord de l'avion de recherche français, le Falcon-20. Le rôle de la pollution sur le développement et l'évolution de l’épisode de précipitation intense du POI7a a été étudié en modifiant la concentration des particules d’aérosol à l’aide de spectres en aérosols observés lors de la campagne de mesures. Les résultats ont montré que la concentration initiale des particules d’aérosol influence la distribution spatiale et la quantité des précipitations, ainsi que le contenu vertical en eau de pluie et en eau glacée du système nuageux précipitant. Pour le cas étudié, une augmentation de la concentration initiale en nombre de particules d’aérosol diminue la quantité totale de pluie au sol. Enfin, une étude de sensibilité supplémentaire sur le choix du domaine de simulation a permis de montrer le rôle essentiel de la dynamique et de l’humidité des basses couches atmosphériques de grande échelle sur la représentation du système précipitant. / The French coastline in the Mediterranean Sea is affected by heavy rainfall episodes especially in autumn. Cévennes – Vivarais, which is part of the Massif Central Mountains, is one of the affected regions. The associated heavy precipitation episodes (HPE), namely “Cévenols”, can cause natural disasters with important economic damages and life losses. The prediction of such episodes by Numerical Weather Prediction (NWP) models has been significantly improved; uncertainties remain though, regarding their occurrence and strength. The improvement of microphysical parameterizations in NWP models is one key-component for the reduction of forecast errors. The aim of this study was provide a better understanding of the microphysical processes that govern HPE and their interaction with atmospheric aerosol particles (APs) by exploiting observations from the HYMEX research program.The present study focused on the HPE from the HYMEX Intense Observation Period (IOP) 7a, whose observations were assessed and compared with modelling results from the bin-resolved microphysics scheme DEtailed SCAvenging Model (DESCAM, Flossmann and Wobrock; 2010) with 3D dynamics. This research model uses a detailed representation of the APs. Observations from ground-based instruments, as well as in-situ measurements were used for the evaluation of the model’s performance. The ground-based dataset consists of X-band Radars, Micro-Rain Radars (MRR), disdrometers, but also a rainfall reanalysis by rain gauges and operational radars (Boudevillain et al. 2016). Moreover, hydrometeor probes and the 95GHz cloud radar RASTA provided observations on-board of the French research aircraft Falcon-20.The role of pollution on the development and evolution of the HPE of IOP7a was investigated, as well. Considering that the highest AP concentrations were observed during IOP7a, the followed strategy was to perform model simulations by using less polluted observed AP spectra with lower total number concentrations. The results showed that the initial AP concentration influences the spatial distribution and quantity of rainfall, as well as the vertical properties of the rain water content and the ice water content of the precipitating cloud system. For the studied cases, with increasing the initial number concentration of APs, the total rain amount was decreased. Finally, the present study revealed a critical role of the model’s large-scale configuration necessary to correctly represent the dynamics.

Os sistemas convectivos da região Amazônica possuem características microfísicas peculiares, que variam de um caráter convectivo marítimo (estação chuvosa) a continental (estação de transição seca-chuvosa). Essas características modulam a eletrificação desses sistemas, porém ainda não se sabe quais são os processos dominantes que intensificam o número de descargas elétricas de uma estação para outra: efeito dos aerossóis, termodinâmico, grande-escala ou topografia? Para responder à essa pergunta, o objetivo deste trabalho foi identificar e quantificar a importância de cada um desses efeitos na eletrificação dos sistemas convectivos da Amazônia. A metodologia foi baseada em análises de dados observacionais do experimento de campo DRYTOWET e em um modelo numérico com parametrizações de transferências de cargas e descargas elétricas. A análise do ciclo anual das descargas elétricas do tipo nuvem-solo (CGs) mostrou que a atividade elétrica dos sistemas precipitantes da região sudoeste da Amazônia aumenta durante a transição da estação seca para a estação chuvosa (Agosto a Setembro), associada aos sistemas convectivos com maior desenvolvimento vertical que acontecem nesse período. Com o estabelecimento da estação chuvosa (Novembro a Março), o número de CGs diminui porém a atividade elétrica ainda se mantêm. A porcentagem desses totais de CGs que tinham polaridade positiva (+CGs) tem média de 12% durante todo o ano, aumentando drasticamente para até 25% em Setembro, durante a transição entre as estações secas e chuvosa. Esse aumento da %+CGs ocorreu simultaneamente ao aumento da poluição atmosférica provocada pela queima de biomassa das pastagens realizada pelos fazendeiros locais, que as preparam para a agricultura e pecuária durante o início das primeiras chuvas. Por outro lado, o aumento da %+CGs das tempestades também ocorreu preferencialmente sobre a área de pastagem do estado de Rondônia. Através da análise de dados de radar dos sistemas precipitantes que ocorreram durante o experimento DRYTOWET, foi constatado que as tempestades positivas (tempestades que produzem mais de 50% de +CGs em 50% de seu tempo de vida) se formaram em ambientes mais secos e com alturas do nível de convecção por levantamento (NCL, altura da base da nuvem) maiores do que as demais tempestades (tempestades negativas), durante todo o experimento mas com maiores diferenças durante o final da estação seca (Setembro-Outubro). Com altura da base da nuvem mais elevada, a espessura da camada quente (ECQ - base da nuvem até a isoterma de 0oC) diminui, aumentando assim a velocidade das correntes ascendentes através de um melhor processamento da energia potencial disponível para convecção (CAPE) devido a um menor entranhamento. O aumento da velocidade das correntes ascendentes dentro da nuvem resulta em tempestades mais profundas e mais intensas. O efeito do aumento do NCL é uma característica das regiões com vegetação de pastagem, onde a razão entre o calor sensível e latente na superfície é maior do que as áreas florestadas, aumentando a altura da camada limite planetária. As diferenças de concentração total e distribuição de tamanho dos aerossóis devido ao aumento da poluição durante a transição entre as estações seca e chuvosa não foram conclusivas quanto a um possível efeito na distribuição de hidrometeoros das tempestade positivas e negativas, uma vez que o ciclo diurno da concentração dos aerossóis acompanha o ciclo diurno da camada limite planetária, que também regula o efeito da ECQ. Simulações numéricas com um modelo 1D de nuvem, acoplado à parametrizações de transferências de cargas elétricas entre hidrometeoros e raios, mostraram que a estrutura termodinâmica da atmosfera foi a maior responsável pela eletrificação das tempestades simuladas, aumentando a velocidade das correntes ascendentes. O efeito do aumento do número de aerossóis, que inibe da fase quente da nuvem e conseqüentemente fortalece a da fase fria da nuvem fornecendo mais vapor e gotículas de nuvem para essa região, provocou a diminuição da quantidade de granizo nas tempestades simuladas e o aumento de partículas agregadas menores, como os flocos de neve e graupel, diminuindo a freqüência de raios. / Amazonian convective systems have unique microphysical characteristics, varying from a maritime convective behavior (rainy season) to a continental behavior (wet-dry transition season). These characteristics modulate the electrification of these systems, however it is still not well understood which are the dominant processes that intensify the frequency of lightning from one season to another: aerosol effect, thermodynamics, large-scale variability, landscape or topography? To answer this question, the objective of this study was to identify and quantify the importance of each one of these effects on the electrification of convective systems over the Amazon. The methodology was based on the analysis of observational data from the field experiment DRYTOWET and a numerical model with charge transfer parameterizations and lightning discharges. The cloud-to-ground (CG) lightning discharges annual cycle presented that the electrical activity of the southwestern Amazonian precipitating systems increased during the transition between the dry and wet seasons (August to September), in association with the convective systems deepening. With the establishment of the wet season (November to March), the number of CGs decreased but the electrical activity continued. The mean annual percentage of cloud-to-ground lightning of positive polarity (+CGs) was 12%, increasing drastically to 25% in September during the transition between the dry and wet seasons. This percentage of +CGs raise happened simultaneously with the increase in the atmospheric pollution due to the pasture biomass burning, held by local farmers to prepare the soil for agriculture and livestock during the begging of first rains. On the other hand, the increase in %+CGs also occurred preferentially over pasture areas of Rondonia state. Through the analysis of radar precipitating systems that occurred during the field campaign DRYTOWET, it was noted that positive thunderstorms (storms that produced more than 50% of +CGs over 50% of their life time) were initiated in drier and higher lift condensation levels (cloud base height) environments than other storms (negative thunderstorms) during all the field experiment, especially in the end of the dry season (September-October). A higher cloud base height is associated with a shallower warm cloud depth (cloud base height to the 0oC isotherm) and consequently less entrainment, increasing the updrafts due to a more efficient processing of the convective available potential energy (CAPE). This increase in updrafts inside the clouds results in deeper and stronger thunderstorms. The higher cloud base heights is a characteristic from pasture regions, where the ratio between sensible and latent heats at surface is greater than forested areas, which increases the top of the planetary boundary layer. The differences in the aerosol total concentration and size distribution, due to the increase in the atmospheric pollution during the transition between the dry and wet seasons, were inconclusive in a possible aerosol effect in the strength of positive and negative thunderstorms, once the aerosol concentration diurnal cycle follows the cycle of the planetary boundary layer, that also regulates the warm cloud depth effect. Numerical simulation of an 1D cloud model, coupled with charge transfer between the hydrometeors, showed that the thermodynamic structure was the main responsible feature for cloud electrification, increasing the updraft velocities. The pollution effect was masked in simulations, which inhibit the warm precipitation and consequently strength the the mixed and cold regions of the cloud, was responsible for an increase in the number of smaller aggregated particles, like snow flakes and graupel, decreasing the electrification and lightning frequency.

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.