Publicações

The urban effect over the lightning activity is a recent subject. The first works start at the end of the 20th century. After this study, many others studies were made to cities in Europe, USA and Brazil. Apparently the urban effect on lightning activity is a combination of thermodynamic effect (Urban Heat Island) due to differential heating of the surface over the cities (thermal hypothesis) and the increasing pollute concentrations in the local atmosphere (aerosol hypothesis), caused mainly by human activity. Thus, this paper aims to carry out a review of four important studies about the influence of urban effect on lightning activity to important areas of Brazil. These studies are: Naccarato et al. (2003), Pinto et al. (2004) and Farias et al. (2008, 2012). The first two studies concluded that there is an increase in lightning activity and a decrease in the percentage of positive CG flashes. The others two papers showed the presence of a weekly cycle in lightning activity over Sao Paulo city.

Drought is documented in causing drawdowns of surface reservoirs and impacting water supplies all over the globe. One such documented case occurred in Southern Brazil, over the Cantareira System (CS), one of the largest in the world, as well as one used to supply 8.8 million customers, including metropolitan São Paulo city. The March 2014 prolonged drought over the region supplying the Cantareira System caused a drop in the reservoirs down to 14.0% of their usable capacity, its lowest recorded level since 1974, the year of commencement of operation. Southeastern South America has a well-defined wet austral summer monsoon, with a marked precipitation regime of more than 800 mm of accumulated precipitation over the region, which was significantly curtailed during the drought episode. The large-scale atmospheric and oceanic patters are investigated to highlight the mechanisms associated with the drought event. In this paper, we investigated possible teleconnections of the capacity of the reservoir and sea surface temperature at remote regions. The Standard Precipitation Index (SPI), used to characterize the severity of precipitation deficiency, illustrates the magnitude and spatial extent of the interruption of precipitation supply. The paper concludes with an analysis of the performance of the seasonal precipitation forecast for December, January and February 2014 produced with the operational seasonal prediction system used at the Center for Weather Forecasts and Climate Studies of the National Institute for Space Research (CPTEC/INPE).

A região Semiárida brasileira é afetada por secas recorrentes que comprometem a agricultura de subsistência da região. Dentre as culturas de subsistência cita-se o milho tendo grande importância na alimentação humana e animal. Devido às secas recursivas, a produtividade dessa cultura é muito baixa na maioria dos municípios dessa região e, consequentemente, afeta a segurança alimentar da população e suprimento de alimentos para os animais. Assim, estudos que gerem ferramentas para monitoramento e prevenção das quebras de safras poderão contribuir para um melhor planejamento por parte dos tomadores de decisão, afim de mitigar os efeitos da seca na agricultura e garantir a segurança alimentar. Visando avançar nos estudos sobre o tema, é objetivo da presente tese avaliar a precisão das estimativas de rendimento de milho na região semiárida do Brasil usando o modelo AquaCrop alimentado por previsões sazonais do modelo Eta, com até quatro meses de antecedência. Para o desenvolvimento da tese serão utilizados dados meteorológicos observados, provenientes do INMET e do CPTEC/INPE, e dados de previsão climática sazonal, provenientes do modelo Eta, dados experimentais da fenologia das culturas de milho e sorgo, disponibilizados pela EMBRAPA e IPA, e informações de produtividade por município, disponibilizadas pelo IBGE, bem como dados de propriedades fisico-hídricas do solo, disponibilizados pela EMBRAPA e IPA e obtidos, também, a partir de funções de pedotransferência, para toda região Semiárida. O período de testes com AquaCrop será de 2001 a 2013. Espera-se que o modelo AquaCrop possa simular o rendimento da cultura de milho para toda região Semiárida do Brasil de maneira eficiente e que os dados de previsão climática possam melhorar a antecedência da previsão de safra.

The objective of this study is to assess the climate simulations and projections over South America using the regional climate Eta Model driven by fully coupled Earth System Model HadGEM2-ES of the Met Office Hadley Centre. The HadGEM2-ES was designed to run the major scenarios for IPCC AR5 and comprises Earth system components such as terrestrial and ocean carbon cycle and tropospheric chemistry. Over the past years the regional climate Eta Model has been used to produce climate change scenarios over South America (Pesquero et al. 2009, Chou et al. 2012, Marengo et al. 2012). In this study, Eta model was configured with 38 vertical layers, 20-km grid size and was run over 19602005 based on historical emissions, and 20062100 based on RCP4.5 scenarios to simulate possible future changes. We have evaluated the regional climate simulation for some areas in Brazil, particularly for Amazon and Northeast, Southeast and South regions of Brazil. Annual cycle of precipitation and surface temperature for these areas was compared with CRU (Climatic Research Unit) observational data. Simulated and projected patterns of mean fields of precipitation, temperature and upper and low-level circulation were analyzed for austral summer and winter. The regional model reproduces reasonably well the spatial patterns of the precipitation and temperature. The downscaling with Eta model improved the simulation of the seasonal cycle of precipitation and temperature over Brazil and some regions when compared with HadGEM2-ES. The projections suggested increases in DJF and JJA temperature of up to 4 °C in continental South America, with more intense changes occurring in the second half of the twenty-first century. The precipitation projections showed the major changes in summer.

Upward lightning from tall objects can be either self-initiated (SIUL), that is, leaders originating due to locally strong electric fields but without any preceding lightning, or triggered by prior lightning discharges in the general vicinity, termed lightning-triggered upward lightning (LTUL). The LTULs can be triggered by (1) nearby +CG return strokes propagating through previous leader networks near the tall object, or (2) the overhead proximity of horizontally propagating negative stepped leaders from either IC or +CGs. Examples of both modes of LTULs are presented. The meteorological environments in which LTULs occur in the U.S. high plains show a strong similarity to the convective regimes (trailing MCS stratiform regions) and the parent lightning which trigger sprites.

Electromagnetic emissions from lightning flashes are observed by a slitless spectrum spectrograph. A Phantom V9.1 high-speed camera is used with a spatial resolution of 1632 x 400 pixels, at 3000 fps and exposure time of 330 μs. A grism (diffraction grating plus prism) that has 600 lines/mm and a spectral ranger 600-1050 nm were coupled to this camera. The lightning observations were made in the city of São José dos Campos (latitude: 23° 11’25.15”S, longitude: 45°53’3.44”W), Sao Paulo, Brazil, focusing on cloud-to-ground lightning events, with both negative or positive polarities. Data from sensors of the BrasilDAT and RINDAT networks were also used to gather additional information (location, polarity and peak current estimation). The objective of this work is to observe for the first time the time-resolved characteristics of lightning emission in the near infrared in Brazil.