A Região Metropolitana de São Paulo (RMSP) conta com mais de 20 milhões de habitantes em 7958 km², o que a caracteriza como uma megacidade. Este fato ocasiona o efeito de ilha de calor que pode resultar em interações complexas com circulações de mesoescala, tais como a brisa marítima, podendo influenciar nos padrões de circulação local e afetar diretamente o tempo e o clima da região. Dessa forma, através da modelagem numérica com o modelo de mesoescala WRF este trabalho se propôs a analisar e avaliar os possíveis efeitos da expansão da mancha urbana - passada e futura - na modificação destes padrões em duas estações do ano de 2007: inverno (18/08) e verão (07/03). Para isto introduziu-se diferentes manchas urbanas no modelo, supondo nenhuma urbanização, urbanização observada em 1952 e em 2007, bem como uma suposta urbanização prevista para o ano de 2030. O acoplamento de um modelo de dossel urbano junto ao WRF também foi avaliado, e os resultados mostraram que para o inverno a inclusão do mesmo se mostrou dispensável, enquanto para o verão as simulações em que o módulo esteve ativo se mostraram mais coerentes à realidade. Para as duas estações observou-se a influência da expansão da mancha urbana nos eventos de brisa marítima, sendo que quanto maior a área urbanizada maior o tempo de deslocamento da frente de brisa continente adentro, podendo a diferença chegar a 2 horas. Diferenças na temperatura também puderam ser vistas, principalmente à noite no período de inverno, de forma que algumas regiões chegaram a apresentar 6 °C a mais em 2007. Observou- se uma frente de umidade acompanhando a frente de brisa marítima e quanto maior a urbanização, menor a quantidade de umidade associada, chegando a uma redução de 22% durante o inverno e de 33% durante o verão. No inverno não foram observadas grandes diferenças na precipitação, enquanto que no verão foram encontradas diferenças significativas em praticamente todo o domínio de simulação, chegando a 50 mm em determinadas regiões (a mais ou a menos). Tais diferenças na precipitação não se mostraram lineares com a expansão da mancha urbana. Cortes verticais não evidenciaram circulações bem definidas associadas à ilha de calor, nem para o inverno nem para o verão, no entanto, claramente pôde-se observar a influência que a expansão urbana tem sobre os episódios de brisa marítima, em quaisquer das variáveis meteorológicas analisadas. / The Metropolitan Area of São Paulo (MASP) has over 20 million inhabitants over a 7958 km² area, which characterizes a megacity. This fact causes the heat island effect that can result in complex interactions with mesoscale circulations such as the sea breeze and can influence the local circulation and directly affect the weather and climate of the region. Therefore, through numerical modeling of the atmosphere using the WRF mesoscale model this work analyses and evaluates the possible effects of urban expansion - past and future on the modification of these patterns in two days representatives of the winter and summer (18/08 and 07/03, respectively). For that purpose we introduced different types of urban areas in the model, assuming no urbanization, using the urbanization observed in 1952 and 2007 as well as a hypothetical urbanization numerically predicted for the year of 2030. The coupling of an urban canopy model (UCM) along with WRF was also evaluated and the results showed that the inclusion of UCM proved to be unnecessary during wintertime. However, in the summer, the simulations where the module was activated were more consistent with reality. For the two seasons we observed the influence of urban expansion in the events of sea breeze, and the higher the urbanized area more increased was the travel time of the sea breeze front inland, being the time difference as high as 2 hours. Differences in temperature were also observed, especially at night in the winter, so that some regions were as high as 6 °C hotter in 2007. A moisture front accompanying the sea breeze front and the higher the urbanization the lower the amount of moisture associated, reaching a reduction of 22% during winter and 33% during the summer. During the winter no major differences were observed in precipitation, while in the summer significant differences were found almost over all simulation domain, reaching 50 mm in certain regions (positive or negative). Such differences in precipitation were not linear with the expansion of urban area. Vertical sections did not show well-defined circulations associated with urban heat island, neither for the winter nor for summer, however, we can clearly observe the influence that urban area extension has on episodes of sea breeze in any of the weather variables.

<p>Three different studies have been made; an analysis of the general weather situation at three weather stations in Svalbard, close to the main settlement Longyearbyen; an instrumental comparison between three weather stations operating at nearly the same place during a few days in October 2006; and a case study of a weather station at the mountain Breinosa compared to the station in the valley beneath.</p><p>The analysis of the general weather at the three stations, Adventdalen (data used from 2004-2006), Svalbard Airport (data used from 1994-2004) and Gruvefjellet (data used from 2002-2005) showed that it is clear that the local surroundings do contribute to a more locally produced weather. The mean wind speed in Adventdalen was shown to be 5.1 m/s and the wind direction was mostly from inland towards the coast. Channelling effects dominates the winds in the valley, resulting in high wind speeds. The channelled winds from Adventdalen often reach Svalbard Airport (average wind speed 4.8 m/s). At the Airport there is also a contribution of winds (mostly in summer) originating from the sea, e.g. sea breeze. In times when the weather at Svalbard Airport was more continental, Adventfjorden and Isfjorden were likely to be covered by ice. The higher location of Gruvefjellet most often contributes to low temperatures and an average wind speed of 3.9 m/s. However, the temperature at Adventdalen and the Airport are often colder than at Gruvefjellet due to the frequency of temperature inversions.</p><p>The instrumental comparison concerned three stations in Adventdalen. Data from the stationary weather station was compared with data from two temporarily stations during 4-7th October 2006. It is apparent that the stationary station needs calibration, at least when looking at the pressure measurements, where there clearly is an offset in the data.</p><p>The third study was a case study concerned data from a station at the mountain Breinosa and Adventdalen. A new weather station will be put up during 2007 and data (16th December 2005 until 12th January 2006) from a temporarily station was used when determining the differences from the station down in the valley (Adventdalen). The wind speed is often just as high in the valley as at Breinosa due to channelling effects. The temperature in Adventdalen seems to be affected by the temperature at Breinosa. The air is chilled and sinks down to be channelled through the valley. There are some occasions when the temperature at the mountain is higher than beneath. During those events the wind speed is low and a temperature inversion develops at the ground.</p> / <p>Tre olika studier genomförts; en analysering av data från tre väderstationer på Svalbard;en instrumentell jämförelse mellan tre väderstationer på Svalbard nära huvudorten Longyearbyen; en fallstudie av data från en väderstation på berget Breinosa jämfört med situationen i Adventdalen nedanför.</p><p>Undersökningen av generella vädersituationen vid de tre stationerna, Adventdalen (data från 2004-2006), Svalbard Flygplats (data från 1994-2004) och Gruvefjellet (data från 2002-2005) visade tydligt att den lokala omgivningen bidrar mycket till hur vädret formas. Medelvindhastigheten i Adventdalen var 5,1 m/s och vindriktningen mestadels längs dalen ut mot fjorden. Kanaliseringseffekter dominerar vindarna i dalen och bidrar till de höga vindhastigheterna. Kanaliserade vindar från Adventdalen når ofta Svalbard Flygplats (medel vindhastighet 4,8 m/s). Vid Flygplatsen finns också ett visst bidrag från vindar utifrån havet (mestadels under sommaren), d.v.s. sjöbris. I situationer då vädret vid flygplatsen varit mer kontinentalt så har Adventfjorden mest troligt varit täckt av is.</p><p>Gruvefjellets höga placering bidrar till låga temperaturer och en medelvindhastighet på 3.9 m/s. Dock är temperaturen är ofta lägre i Adventdalen och vid Flygplatsen på grund av att det ofta förekommer temperaturinversioner i marknivå.</p><p>Den instrumentella jämförelsen berörde tre stationer i Adventdalen. Data från den stationära stationen jämfördes under 4-7 oktober 2006 med data från två temporära stationer. Det är tydligt att den stationära stationen är i behov av kalibrering. I alla fall är det uppenbart vid studien av lufttrycket som tydligt är förskjutet och visar ett lägre tryck.</p><p>Tredje studien var en fallstudie och data undersöktes från berget Breinosa och Adventdalen. En ny väderstation kommer att monteras på Breinosa under 2007 och data (16 december 2005 till 12 januari 2006) från en temporär station användes i studien. Vindhastigheten är ofta lika hög i dalen som på berget på grund av kanaliseringseffekter. Temperaturen i dalen förefaller vara påverkad av temperatursituationen på berget. Avkyld luft sjunker och kanaliseras ner i dalen. Det finns några tillfällen då temperaturen på berget Breinosa är högre än nere i dalen. Under de situationerna avtar vindhastigheten och en temperaturinversion bildas i marknivå.</p>

Three different studies have been made; an analysis of the general weather situation at three weather stations in Svalbard, close to the main settlement Longyearbyen; an instrumental comparison between three weather stations operating at nearly the same place during a few days in October 2006; and a case study of a weather station at the mountain Breinosa compared to the station in the valley beneath. The analysis of the general weather at the three stations, Adventdalen (data used from 2004-2006), Svalbard Airport (data used from 1994-2004) and Gruvefjellet (data used from 2002-2005) showed that it is clear that the local surroundings do contribute to a more locally produced weather. The mean wind speed in Adventdalen was shown to be 5.1 m/s and the wind direction was mostly from inland towards the coast. Channelling effects dominates the winds in the valley, resulting in high wind speeds. The channelled winds from Adventdalen often reach Svalbard Airport (average wind speed 4.8 m/s). At the Airport there is also a contribution of winds (mostly in summer) originating from the sea, e.g. sea breeze. In times when the weather at Svalbard Airport was more continental, Adventfjorden and Isfjorden were likely to be covered by ice. The higher location of Gruvefjellet most often contributes to low temperatures and an average wind speed of 3.9 m/s. However, the temperature at Adventdalen and the Airport are often colder than at Gruvefjellet due to the frequency of temperature inversions. The instrumental comparison concerned three stations in Adventdalen. Data from the stationary weather station was compared with data from two temporarily stations during 4-7th October 2006. It is apparent that the stationary station needs calibration, at least when looking at the pressure measurements, where there clearly is an offset in the data. The third study was a case study concerned data from a station at the mountain Breinosa and Adventdalen. A new weather station will be put up during 2007 and data (16th December 2005 until 12th January 2006) from a temporarily station was used when determining the differences from the station down in the valley (Adventdalen). The wind speed is often just as high in the valley as at Breinosa due to channelling effects. The temperature in Adventdalen seems to be affected by the temperature at Breinosa. The air is chilled and sinks down to be channelled through the valley. There are some occasions when the temperature at the mountain is higher than beneath. During those events the wind speed is low and a temperature inversion develops at the ground. / Tre olika studier genomförts; en analysering av data från tre väderstationer på Svalbard;en instrumentell jämförelse mellan tre väderstationer på Svalbard nära huvudorten Longyearbyen; en fallstudie av data från en väderstation på berget Breinosa jämfört med situationen i Adventdalen nedanför. Undersökningen av generella vädersituationen vid de tre stationerna, Adventdalen (data från 2004-2006), Svalbard Flygplats (data från 1994-2004) och Gruvefjellet (data från 2002-2005) visade tydligt att den lokala omgivningen bidrar mycket till hur vädret formas. Medelvindhastigheten i Adventdalen var 5,1 m/s och vindriktningen mestadels längs dalen ut mot fjorden. Kanaliseringseffekter dominerar vindarna i dalen och bidrar till de höga vindhastigheterna. Kanaliserade vindar från Adventdalen når ofta Svalbard Flygplats (medel vindhastighet 4,8 m/s). Vid Flygplatsen finns också ett visst bidrag från vindar utifrån havet (mestadels under sommaren), d.v.s. sjöbris. I situationer då vädret vid flygplatsen varit mer kontinentalt så har Adventfjorden mest troligt varit täckt av is. Gruvefjellets höga placering bidrar till låga temperaturer och en medelvindhastighet på 3.9 m/s. Dock är temperaturen är ofta lägre i Adventdalen och vid Flygplatsen på grund av att det ofta förekommer temperaturinversioner i marknivå. Den instrumentella jämförelsen berörde tre stationer i Adventdalen. Data från den stationära stationen jämfördes under 4-7 oktober 2006 med data från två temporära stationer. Det är tydligt att den stationära stationen är i behov av kalibrering. I alla fall är det uppenbart vid studien av lufttrycket som tydligt är förskjutet och visar ett lägre tryck. Tredje studien var en fallstudie och data undersöktes från berget Breinosa och Adventdalen. En ny väderstation kommer att monteras på Breinosa under 2007 och data (16 december 2005 till 12 januari 2006) från en temporär station användes i studien. Vindhastigheten är ofta lika hög i dalen som på berget på grund av kanaliseringseffekter. Temperaturen i dalen förefaller vara påverkad av temperatursituationen på berget. Avkyld luft sjunker och kanaliseras ner i dalen. Det finns några tillfällen då temperaturen på berget Breinosa är högre än nere i dalen. Under de situationerna avtar vindhastigheten och en temperaturinversion bildas i marknivå.

Methane measurements over lake Tämnaren show a pronounced diurnal variation with high values at night and low values during daytime. The atmosphere over the lake and its surroundings is simulated with two different settings and resolutions of the WRF model during a period of eight days in May 2011 to investigate if a lake/land breeze circulation could be the cause of the observed methane variation. A night time land breeze can give rise to convergence over Tämnaren of the natural methane emissions from the lake which possibly could explain the diurnal variation. Analysis show that although Tämnaren is large enough to initiate a fully closed circulation these events are likely going to be rare because of the strong dependence of the background wind speed and cannot therefore be the cause of the pronounced diurnal variation. A fairly moderate wind speed will dominate over the thermodynamical forcing necessary to create a lake breeze. Even so, it is possible that a closed or nearly closed circulation could enhance the diurnal pattern with an increase of methane concentration at night and a decrease during the day. The reason for the high night time methane concentration is more likely due to the accumulation in a shallow internal boundary layer that develops over the lake combined with high night time methane flux caused by waterside convection. / Mätningar av metankoncentrationen över Tämnaren visar en tydlig dygnsvariation med höga värden på natten och låga under dagtid. Atmosfären över sjön med omgivning modelleras med två olika inställningar och upplösningar av WRF modellen under en åttadagarsperiod i Maj 2011 för att undersöka om en sjö- och landbriscirkulation kan vara orsaken till den observerade metanvariationen. På natten kan en landbris ge upphov till konvergens över Tämnaren av de naturliga metanutsläppen vilket skulle kunna vara en möjlig förklaring till dygnsvariationen. Vidare analys visar att Tämnaren är tillräckligt stor för att initiera en sluten cirkulation men dessa händelser är troligtvis sällsynta på grund av det starka inflytandet av bakgrundsvinden och kan därför inte vara orsaken till den uttalade metanvariationen. En relativt måttlig vind kommer dominera över den termodynamiska effekt som är drivande för skapandet av sjö- och landbris. Trots detta är det möjligt att en sluten eller nästan sluten cirkulation kan förstärka metanhaltens dygnsvariation med en ökning på natten och minskning under dagen. Orsaken till den observerade höga metankoncentrationen på natten är troligare en ackumulering i ett grunt internt ytskikt som bildas över Tämnaren kombinerat med höga nattliga metanflöden till följd av konvektion i sjön.

A Região Metropolitana de São Paulo (RMSP) conta com mais de 20 milhões de habitantes em 7958 km², o que a caracteriza como uma megacidade. Este fato ocasiona o efeito de ilha de calor que pode resultar em interações complexas com circulações de mesoescala, tais como a brisa marítima, podendo influenciar nos padrões de circulação local e afetar diretamente o tempo e o clima da região. Dessa forma, através da modelagem numérica com o modelo de mesoescala WRF este trabalho se propôs a analisar e avaliar os possíveis efeitos da expansão da mancha urbana - passada e futura - na modificação destes padrões em duas estações do ano de 2007: inverno (18/08) e verão (07/03). Para isto introduziu-se diferentes manchas urbanas no modelo, supondo nenhuma urbanização, urbanização observada em 1952 e em 2007, bem como uma suposta urbanização prevista para o ano de 2030. O acoplamento de um modelo de dossel urbano junto ao WRF também foi avaliado, e os resultados mostraram que para o inverno a inclusão do mesmo se mostrou dispensável, enquanto para o verão as simulações em que o módulo esteve ativo se mostraram mais coerentes à realidade. Para as duas estações observou-se a influência da expansão da mancha urbana nos eventos de brisa marítima, sendo que quanto maior a área urbanizada maior o tempo de deslocamento da frente de brisa continente adentro, podendo a diferença chegar a 2 horas. Diferenças na temperatura também puderam ser vistas, principalmente à noite no período de inverno, de forma que algumas regiões chegaram a apresentar 6 °C a mais em 2007. Observou- se uma frente de umidade acompanhando a frente de brisa marítima e quanto maior a urbanização, menor a quantidade de umidade associada, chegando a uma redução de 22% durante o inverno e de 33% durante o verão. No inverno não foram observadas grandes diferenças na precipitação, enquanto que no verão foram encontradas diferenças significativas em praticamente todo o domínio de simulação, chegando a 50 mm em determinadas regiões (a mais ou a menos). Tais diferenças na precipitação não se mostraram lineares com a expansão da mancha urbana. Cortes verticais não evidenciaram circulações bem definidas associadas à ilha de calor, nem para o inverno nem para o verão, no entanto, claramente pôde-se observar a influência que a expansão urbana tem sobre os episódios de brisa marítima, em quaisquer das variáveis meteorológicas analisadas. / The Metropolitan Area of São Paulo (MASP) has over 20 million inhabitants over a 7958 km² area, which characterizes a megacity. This fact causes the heat island effect that can result in complex interactions with mesoscale circulations such as the sea breeze and can influence the local circulation and directly affect the weather and climate of the region. Therefore, through numerical modeling of the atmosphere using the WRF mesoscale model this work analyses and evaluates the possible effects of urban expansion - past and future on the modification of these patterns in two days representatives of the winter and summer (18/08 and 07/03, respectively). For that purpose we introduced different types of urban areas in the model, assuming no urbanization, using the urbanization observed in 1952 and 2007 as well as a hypothetical urbanization numerically predicted for the year of 2030. The coupling of an urban canopy model (UCM) along with WRF was also evaluated and the results showed that the inclusion of UCM proved to be unnecessary during wintertime. However, in the summer, the simulations where the module was activated were more consistent with reality. For the two seasons we observed the influence of urban expansion in the events of sea breeze, and the higher the urbanized area more increased was the travel time of the sea breeze front inland, being the time difference as high as 2 hours. Differences in temperature were also observed, especially at night in the winter, so that some regions were as high as 6 °C hotter in 2007. A moisture front accompanying the sea breeze front and the higher the urbanization the lower the amount of moisture associated, reaching a reduction of 22% during winter and 33% during the summer. During the winter no major differences were observed in precipitation, while in the summer significant differences were found almost over all simulation domain, reaching 50 mm in certain regions (positive or negative). Such differences in precipitation were not linear with the expansion of urban area. Vertical sections did not show well-defined circulations associated with urban heat island, neither for the winter nor for summer, however, we can clearly observe the influence that urban area extension has on episodes of sea breeze in any of the weather variables.

Eventos de brisa marítima (BM) são comuns na Região Metropolitana de São Paulo (RMSP). No verão, em particular, estão associados com tempestades, chuvas, rajadas de vento, granizo e descargas atmosféricas intensas na RMSP. Utilizou-se o método de OLIVEIRA e SILVA DIAS (1982) para identificar os eventos de BM. Todos os eventos de BM entre 2005 e 2008 foram analisados por meio de medições de superfície, altitude, radares meteorológicos, satélite e modelagem numérica da atmosfera. Em geral, a penetração da frente de BM na RMSP ocorre entre o meio e o fim da tarde com aumento da temperatura do ponto de orvalho. Ainda, o ambiente urbano mais aquecido tende a intensificar as tempestades que podem produzir enchentes, alagamentos, queda de árvores, entre outros impactos socioeconômicos muito significativos. A partição anual pluviométrica devido a BM foi estimado com o radar meteorológico de São Paulo. Os resultados indicam um núcleo de máxima precipitação acumulada com pico de 600 mm sobre a RMSP, muito maior que no entorno dessa. A modelagem com o ARPS permitiu simular condições médias espaciais em baixos, médios e altos níveis de diversas variáveis dos eventos analisados. As simulações de controle e específicas com ARPS sugerem um impacto significativo da cobertura do solo na distribuição espacial da precipitação. As análises foram complementadas com medições do radar meteorológico MXPOL e demonstram a importância desse tipo de sensoriamento remoto na detecção e previsão a curtíssimo prazo da penetração de BM, com alta resolução espaço-temporal. / Sea breeze events (SB) are common in Metropolitan area at São Paulo (MASP). Particularly, in the summer, SB triggers over MASP deep convection, heavy rainfall, wind gusts, hail and lightning. OLIVEIRA and SILVA DIAS (1982) method was used to identify the SB events. SB events between 2005 and 2008 were analysed by means of surface and upper air measurements, weather radar, satellite and numerical modelling. In general, the SB front penetrates in MASP between midafternoon and evening increasing dew point. Moreover, the warmer urban environment tends to intensify storms that produce flooding, falling trees, among other large socioeconomic impacts. The annual rainfall partition due to SB was estimated using the São Paulo weather radar. The results indicate a core of maximum rainfall accumulation of 600 mm over MASP, much larger than that in the vicinity. The modelling with ARPS allowed simulate conditions spatial average in low, medium and upper levels of several variables of the analysed events. Moreover, the ARPS system was used to simulate SB with control and specific runs. Results suggest significant impact of surface cover on rainfall distribution. MXPOL weather radar measurements of SB were important in detecting and nowcasting SB inflow at very high spatial and temporal resolution.

Longshore sediment transport rate was measured during energetic sea breeze activity, on intermediate-to-reflective sandy beaches in Southwestern Australia. Estimates of suspended load were obtained using backscatter sensors, current meters and streamer traps. Total load was determined using fluorescent tracer sand and an impoundment study. The measurementsw ere cross-compareda nd usedt o evaluates everalw idely-used longshore transport equations. The streamer trap measurement revealed an exponential distribution of the suspended sediment flux with vertical mixing decreasing in the onshore direction. A continuous time series of the longshore suspended sediment flux across the surf zone was obtained by combining the streamer trap measurements with data collected using surf zone instruments. Comparison of the suspended longshore flux with the total longshore flux derived from the dispersal of the sand tracer indicated that the relative contribution of the suspendedlo ad to the total load was at least 59 %. The movement of sandt racer on four different beaches demonstrated that nearshore sediments were transported obliquely across the surf zone, challenging our conventional view of dividing nearshore sediment transport into cross-shore and longshore components. Furthermore, tracer was found to move from the outer surf zone to the swash zone and vice versa, indicating a cross-shore sediment exchange. The contribution of the swash zone to the total longshore flux was estimated around 30-40 %. Despite large differences in the temporal and spatial scales of the measurement techniques, the littoral drift rates are comparable, suggesting a northward transport rate of 138,000-200,000 m3 year-1. Longshore sediment transport during sea breezes is mainly the result of a high longshore energy flux exerted by wind waves. This is accurately predicted by the equations of Inman and Bagnold (1963) and CERC (1984). The bimodal wave field, characteristic of Southwestern Australia, renders the Kamphuis (1991b) formula unsuitable in this instance.

This study investigates how well the Regional Atmospheric Modelling System (RAMS) simulates the sea breeze from False Bay (False Bay sea breeze) at a small resolution of 200m. It describes the influence of the sea breeze in the Stellenbosch wine growing district focusing on temperature, relative humidity and wind speed and direction through three case studies, using three different synoptic conditions. The RAMS simulations are verified against measurements done by automatic weather stations in the study area for all three case studies. The first synoptic condition investigated is when light onshore flow occurred over the south-western Cape. The RAMS model simulated the vertical and horizontal structure of the sea breeze from False Bay very well. However RAMS predicted the onset of the sea breeze 3 hours earlier than the AWS data predicted. The flow was off-shore in the second case study. The RAMS simulations as well as the observed data from the automatic weather stations, showed the two sea breezes influencing the study area, one from Table Bay, west of Stellenbosch, and one from False Bay. In this case study the model simulated the flatter head and stronger False Bay sea breeze. The third case study investigated the influence of strong onshore synoptic conditions, in which the model and observed values showed that no sea breeze developed from False Bay. From the three case studies it was found that the sea breeze is influenced by the synoptic flow and that the sea breeze causes cooling of between 3°C and 16°C and relative humidity (RH) increase of between 16 – 57% depending on the synoptic flow. RAMS was able to simulate the sea breeze theoretically correct and has the potential to be used to identify climatological areas in the wine growing areas of the Western Cape. / Dissertation (MSc)--University of Pretoria, 2007. / Geography, Geoinformatics and Meteorology / Unrestricted

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.