The sky view factor (SVF) is an important radiometric parameter for assessing the canopy energy budget of urban areas. There are several methods to determine the SVF observationally. The most common ...is taking a photo with a digital camera equipped with a fish-eye lens and then converting ratio of sky area to canopy area into SVF. However, most urban canopy models use this variable as derived from idealized canopy geometry. To evaluate the effect of inputting observed SVFs in numerical models, we evaluated a mesoscale model’s performance in reproducing surface wind and surface temperature when subjected to different ways of SVF prescription. The studied area was the Metropolitan Area of São Paulo (MASP) in Brazil. Observed SVFs were obtained for 37 sites scattered all over the MASP. Three simulations, A, B, and C, with different SVF and aspect-ratio prescriptions, were performed to analyze the effect of SVF on the urban canopy parameterization: Simulation A (standard) used the original formulation of the Town Energy Budget (TEB) model, computing the SVFs from the aspect-ratios; Simulation B used the observed SVFs, but keeps aspect-ratios as original; and Simulation C used the aspect-ratios computed from observed SVFs. The results show that in general inputting observed SVFs improves the model capability of reproducing temperature at surface level. The comparison of model outputs with data of regular meteorological stations shows that the inclusion of observed values of SVFs enhances model performance, reducing the RMSE index by up to 3 ∘C. In this case, the model is able to better reproduce the expected effects in the wind field, and consequently the temperature advection, of the urban boundary layer to a large urban area. The result of Simulation C shows that the surface wind and temperature intensity for all urban types is higher than those of Simulation A, because of the lower values of the aspect ratio. The urban type with high density of tall buildings increase up to 1 ms-1 in the wind speed, and approximately 1 ∘C in temperature, showing the importance of a better representation of the urban structure and the SVF database improvement.
In the context of the impact of urbanization on climate change, this work aims to evaluate the sensitivity of the thermal and radiative properties of building surfaces in urban areas to the urban ...heat island intensity, a local scale meteorological phenomenon. For this, variations of albedo values, emissivity, thermal conductivity and heat capacity of roofs, streets and walls were simulated through an urban scheme coupled with the BRAMS mesoscale atmospheric model for the metropolitan area of São Paulo, considering two main urban types. The simulations show that, in general, looking for cold surface situations, the change of building material can contribute to a reduction of up to 3 °C for São Paulo. In addition, the role of orientation and the typological characteristics of constructions should be taken into account. In this sense, it is expected that this work guides civil engineers and builders to search for new materials in order to reduce the effects of urbanization on the local climate.
One of the central problems in large cities is air pollution, mainly caused by vehicular emissions. Tropospheric ozone is an atmospheric oxidizing gas that forms in minimal amounts naturally, ...affecting peoples’ health. This pollutant is formed by the NO2 photolysis, creating a main peak during the day. Nighttime secondary peaks occur in several parts of the world, but their intensity and frequency depend on the local condition. In this sense, this works aims to study the local characteristics for tropospheric nocturnal ozone levels in the Metropolitan Area of São Paulo, in Brazil, using the Simple Photochemical Module coupled to the Brazilian Developments on the Regional Atmospheric Modeling System. For this, three different situations of nocturnal occurrence were studied. The results show that the nocturnal maximum of ozone concentrations is related to the vertical transport of this pollutant from higher levels of the atmosphere to the surface and is not related to the synoptic condition.
According to IPCC reports, global climate change is likely to be accompanied by a greater frequency, intensity, and duration of heat waves in urban areas. This is related to predicted and ongoing ...variation of atmospheric temperature and its association with the dynamical evolution of cities. Changes in the roughness pattern of the surface, wind intensity, soil available humidity and radiative properties compared to the natural surfaces characterize the formation of the Urban Heat Island (UHI). A dynamical downscaling of A2 and B1 SRES's future scenarios from Intergovernmental Panel on Climate Change were performed for Londrina, a medium-size city of Southern Brazil, using the Weather Research and Forecasting model. The main objective of this study is to investigate the impact of these scenarios on the UHI formation and intensity based on different input data, and its role and influence in the rural area. For this, an evaluation of the model and a comparison with the scenarios were done to mitigate the current trends. The results show a tendency in the current situation in following the pessimistic A2 scenario. Also, a drier rural area for the sustainable projection (B1) is found which implicates in a higher temperature and wind patterns modification for both sites, urban and rural region. Both future projections have a direct influence on the UHI intensity and formation, yielding effects in the agriculture and affecting conditions on human comfort over the region.
This paper presents a simple method to obtain urban effective albedo based on the sky-view factor (SVF) data. In the method described herein, a two-dimensional canyon is the prototype to model the ...urban geometry. To obtain the effective albedo for urban areas, surface albedo values of different facets (roof, wall and road) are assumed. The effective albedo changes with respect to the sky-view factor so that the starting point was to make use of a digital camera equipped with a fish-eye lens to obtain the sky-view factor for 36 sites located in the Metropolitan Area of São Paulo (MASP). To easily compute the effective canyon albedo from the local SVFs, it was assumed that the shortwave radiation in the interior of the canyon is reflected on walls and street infinitely-many times. The model was capable to reproduce the evolution of effective albedo for the center of MASP. The SVF decreases with increasing building coverage or increasing building height, enabling a higher values of the urban heat island intensity. Even not take into account the role of plan built area density or the facade density, this work could attribute a value of 0.5 based on the literature.
•Sky-view factors (SVFs) were obtained using a fish-eye lens for São Paulo.•Solar radiation scheme considers infinite reflections.•The scheme is applied to obtain the effective albedo.•Relationship between effective albedo and SVF is almost linear at midday.
The representation of the influence of vegetation on meteorological variables inside the urban canopy is a modeling challenge. The interaction of vegetation canopy parameterization for urban regions ...in mesoscale modeling was implemented and analyzed in this work. The BRAMS model equipped with the TEB was used to simulate a calm wind and clear sky period in the Metropolitan Area of São Paulo. The impact of vegetated areas on cities was estimated by calculating the surface fluxes due to vegetation and artificial materials, weighing individual contributions by using each component fraction inside a model grid. An evaluation of the vegetation impact on atmospheric conditions was made by comparing simulated temperature and specific humidity with surface observations, atmospheric sounding values and land-surface temperature product retrieved from MODIS/TERRA. The inclusion of vegetation clearly improves the simulated air temperature, the vertical structure of the urban boundary layer and the calculation of surface fluxes. Although some improvements in the model are still necessary, it is clear that the model is very sensitive to the presence of the vegetation and continuous efforts should be made to better understand the related process and to provide better tools for urban planning and other important activities in urban areas.
•An urban-vegetation parameterization with weighting turbulent fluxes is evaluated.•Inclusion of urban vegetation provides better accuracy for mesoscale simulations.•Modeling vegetation is important even for cities with low index of green areas.
According to IPCC reports, a greater frequency, intensity and duration of heat waves in urban areas are expected. This is related to the dynamical evolution of the cities, due the changes of the ...natural surface modifies the roughness pattern reduce the wind intensity, modify the available humidity in the soil and the radiative properties. These topics characterize the formation of the urban heat island (UHI). A dynamical downscaling of A2 and B1 future scenarios was made for Londrina, a medium-size city of Southern Brazil, using Weather Research Forecasting model, to investigate the impact of this projections on the UHI formation and intensity, as well for rural area, which consistent an important agricultural landscape. For this, an evaluation of the model and the scenarios were done to investigate the current trends. The results shows a tendency of following the worst proposed scenarios (A2), and a drier rural area for the sustainable projection, which has directly influence on the urban heat island intensity and formation, and in the agriculture of the region.
O presente trabalho teve por objetivo caracterizar as circulações locais que se formam na região central do Chile (RCC). Uma análise sinótica para o ano 2004 mostrou que durante o verão a condição de ...tempo dominante foi de céus claros associados à presença do Anticiclone Subtropical do Pacífico Sul com o deslocamento de baixas pressões litoral que mudam o regime de ventos. Dados da Armada do Chile mostraram que, no litoral da Região de Valparaíso, a amplitude anual de temperatura é de aproximadamente de 8 ºC. Os extremos de temperatura ocorrem entre as 09 e 12 UTC para as mínimas e 18 e 21 UTC para as máximas. O vento apresenta um ciclo anual com domínio da componente oeste no verão e componente leste no inverno. Maiores intensidades estão associadas à passagem de sistemas frontais no inverno. A brisa marítima é melhor caracterizada nos valores médios horários do vento no período de verão, sendo observada a partir das 12 UTC, com ventos de maior intensidade entre 18 e 21 UTC. A brisa terrestre é observada a partir das 00 UTC com ventos de menor intensidade que na brisa marítima. Dados da CONAMA-RM mostraram um ciclo diurno de temperatura bem definido na Região Metropolitana de Santiago com as temperaturas mínimas ocorrendo entre 06 e 09 HL e valores máximos entre 14 e 16 HL. Ao agrupar as estações localizadas dentro e fora dos limites urbanos foi possível identificar o efeito da ilha de calor (IC). Para o período de verão a IC apresentou intensidades positivas e no inverno uma maior freqüência de valores negativos. A intensidade do vento sofre também os efeitos da cidade, observando-se uma redução desta nas estações que se localizam no centro da Grande Santiago. Valores mínimos de intensidade do vento por períodos prolongados levaram a um incremento nas concentrações de material particulado. A diminuição nas concentrações está associada à passagem de frentes e ao incremento na intensidade do vento. Os efeitos da cidade na atmosfera foram estudados com mais detalhamento mediante a utilização do BRAMS. A análise sinótica mostrou uma região de vento fraco e baixo gradiente barométrico na região de estudo para a maior parte do período. Foi possível identificar a brisa marítima com maior intensidade do vento entre 18 e 19 UTC. A brisa terrestre foi identificada na maior parte das noites, com intensidade de vento maior próximo das 04 UTC. As cidades localizadas na RCC apresentam a tendência de resfriar o ar próximo da superfície e modificam a intensidade do vento e os padrões de umidade relativa. Embora os efeitos das cidades tenham sido encontrados, os efeitos da topografia no escoamento são ainda mais importantes, gerando circulações sobre a região central do Chile que não são completamente modificadas pela presença das cidades.
The objective of this work was to characterize the local circulations that are generated in the Central Chile (CC) region. A synoptic analyze for 2004 show that clear sky weather conditions associated to the Subtropical Anticyclone of South Pacific (SASP) was dominant during the summer. Coastal lows moving from north to CC interacts with SASP changing the wind regime. Meteorological data from Armada do Chile showed that on the coast of Valparaíso, the annual temperature amplitude was approximately 8 ºC. Temperature extremes occur between 09 and 12 UTC for minimum and 18 and 21 UTC for maximum values. The wind showed an annual cycle, with dominant direction to west during summer, while in wintertime, wind dominant direction is to the east. Higher values of wind speed are associated with frontal passages during winter. The sea breeze was better seen in the wind mean hourly values between 12 UTC and 21 UTC with higher wind speeds at 18 UTC. Land breeze was observed around 00 UTC, with lower wind speeds than in the sea breeze case. Meteorological data form CONAMA-RM showed a well defined diurnal cycle of temperature in the Metropolitan Region of Santiago with minimum temperatures occurring between 06 and 09 LT and maximum values between 14 and 16 LT. The urban heat island effect was seen grouping urban and non urban meteorological stations. The urban heat island is, in general, positive during the summer but, during the winter, negative values of intensity are frequent. The wind speed also shows the urban effects, with a wind speed decrease in the meteorological station inside the city. Long periods of low wind speed are associated with an increase in the particulate matter concentrations. The decrease in these concentrations is associated with the passage of frontal systems, as well as wind speed increase. The city effects on the atmosphere were studied in more details through the use of BRAMS. The synoptic analysis showed a weak wind region and low pressure gradient in the study region for most part of the period. The sea breeze was identified with higher wind speeds between 18 and 19 UTC. The land breeze was identified in the most part of the nights, with higher wind speeds near 04 UTC. The cities situated in CC have a tendency to cool down the air near to the surface and modify the wind speed and relative humidity patterns. Although the effects of the cities have been found, the topography effects on the wind flow are even more important, generating circulations over Central Chile that are not completely modified by the presence of the cities.
Este trabalho teve como objetivo analisar as condições meteorológicas favoráveis e desfavoráveis à dispersão de poluentes, com ênfase no ozônio, nas áreas urbanas associadas à Região Metropolitana de ...São Paulo (RMSP) e a Grande Santiago (GS). Medidas de concentração de estações localizadas em ambas as áreas de estudo foram utilizadas para determinar o comportamento médio, o número de ocorrências de ultrapassagens de padrão de qualidade do ar e o aumento noturno das concentrações de ozônio num período de dez anos. Foi encontrado que o máximo horário acontece próximo das 14 horas (horário local) nas duas regiões, e que existe uma tendência à diminuição no número de ultrapassagens do padrão de qualidade do ar associado a este poluente. Na RMSP é possível observar um máximo secundário durante a madrugada, enquanto que este fenômeno não é claramente observado nos valores médios de concentração na GS. Com dados da Reanálise do NCEP/NCAR foi visto que a ocorrência deste fenômeno está associada a configurações sinóticas específicas na GS, enquanto que na RMSP não existe padrão sinótico específico que diferencie casos com e sem aumento de ozônio noturno. Um novo módulo fotoquímico (NPM), contendo 95 reações foi inserido no modelo BRAMS na tentativa de melhorar o prognóstico das concentrações de poluentes, principalmente em relação ao ozônio. O NPM mostrou melhor desempenho que o módulo fotoquímico original do modelo (SPM; Simple Photochemical Module) para todos os poluentes considerados, salvo o ozônio, para o qual o SPM apresentou melhores índices estatísticos em 5 das 7 estações avaliadas. As características locais associadas à ocorrência simultânea ou não de aumento na concentração de ozônio foram estudadas utilizando o modelo BRAMS com o módulo SPM ativado, sendo verificado que o aumento de ozônio na RMSP está associado, principalmente, ao transporte vertical deste poluente a partir de níveis mais elevados da atmosfera, enquanto que o transporte horizontal é a maior contribuição para o aumento das concentrações de ozônio durante o período noturno na GS.
This work aimed to analyze the favorable and unfavorable meteorological conditions for pollutant dispersion, especially ozone, at the Metropolitan Area of São Paulo (MASP) and the Greater Santiago (GS). Ozone concentration measurements from stations located in both urban areas were used to determinate the mean behavior, the number of standard air quality exceedances and the increase on nocturnal ozone concentration over a 10 years period. It was found that the diurnal maximum occurs around 14 local time in both urban areas, and that there is a diminishment tendency of the total cases of standard air quality exceedances during all period. A secondary maximum of ozone concentration was observed in MASP at night, which was not clearly seen on mean values over GS. By using the NCEP/NCAR Reanalysis data it was seen that the occurrence of this phenomenon is associated to specific synoptic patterns for GS, while there is no specific synoptic pattern for the MASP cases, with or without nocturnal increase in ozone concentrations. A New Photochemical Module (NPM), containing 95 reactions was coupled to BRAMS model in an attempt to improve the prediction of air pollutants, especially ozone. The NPM showed a better performance than the original module, the SPM (Simple Photochemical Module), for all considered pollutants but ozone. For this pollutant, the SPM presents better statistical indexes for 5 of the 7 stations analyzed. The local characteristics related to simultaneous occurrence of nocturnal ozone increase was studied using the SPM-BRAMS model, which showed that the secondary nocturnal maximum of ozone concentrations in MASP are related to vertical transport of this pollutant from higher levels of the atmosphere to the surface, while the horizontal transport is a major contributor to the increase of ozone concentrations in the GS during the night.
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