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Positive flashes correspond to approximately only 10\% of the total number of flashes produced by a thunderstorm. However, strokes with high peak currents and long continuing currents are usually present in positive flashes. Therefore, positive flashes are responsible for more intense damage than the negative ones. Positive flashes often are preceded by significant and long duration intracloud (IC) discharge activity. We observe in detail the electric field variations produced by 80 cloud-to-ground lightning flashes in 9 different storms in S. Paulo, Brazil during the summers of 2009-2011. Intracloud discharges preceding the positive cloud-to-ground flashes and some characteristics of the electric field changes produced by the return stroke that occurred at ranges of 3-80 km from the site of the electric field measurements were analyzed. All flashes presented breakdown pulses prior to the return stroke. The mean time interval between the preliminary breakdown pulse (PBP) and return stroke was 157 ms. The pulse train duration have a mean value of 3.1 ms. Only 6 out of 80 cases analyzed did not present pulse trains but only one single bipolar breakdown pulse before the return stroke. In 95\% of cases the initial breakdown pulse presented the same initial polarity of the succeeding return stroke. Time interval between pulses in a pulse train had a mean value of 280 mu s. The mean values of pulse width is 25.2 mu s. The mean values of zero-to-peak risetimes and of the 10-90\% risetimes for 72 return strokes electric field waveforms are 9.5 and 5.7 mu s respectively. The AM value of peak amplitudes of the positive return strokes fields normalized to 100 km is 17.0 V/m.

Brazils wind energy production has escalated up recently. However, the long-term wind projects do not include the yet unknown impacts of climate changes on wind power. This work is an assessment of these impacts by applying forecasts of a climate model and trend analysis over climatological time series from selected ground sites. Findings indicate a favourable scenario for wind power exploitation in Brazil on the long run.

Temos o prazer de apresentar o 3º Relatório de Atividades do Instituto Nacional de Ciência e Tecnologia para Mudanças Climáticas (INCT para MC), que resume os destaques científicos de seus 26 sub-projetos de pesquisa, no período de setembro de 2011 a março de 2013. O documento traz ainda uma descrição resumida dos objetivos, da organização, da infraestrutura e do processo de formação de recursos humanos desta que constitui a maior e mais abrangente rede interdisciplinar de instituições de pesquisa em meio ambiente no Brasil.

Quando visitou o Reino Unido em março de 2006, o presidente Lula firmou um acordo de trabalho conjunto entre Reino Unido e Brasil sobre questões relativas às mudanças climáticas. Atualmente os dois países ainda continuam trabalhando juntos, com o mesmo senso de urgência que a visita do presidente inspirou, para avaliar os impactos das mudanças climáticas e os efeitos do desmatamento sobre o clima do Brasil. Este relatório destaca o que se conseguiu até agora por meio da cooperação e da engenhosidade do INPE e o Met Office Hadley Centre (MOHC).

Agreement for the UK and Brazil to work together on climate-change issues was reached when President Lula visited the UK in March 2006. Today, our two countries still work together, with the same sense of urgency his visit inspired, to assess the impacts of climate change on Brazil and the effects of deforestation on the Brazilian climate. This report highlights what has been achieved so far through the cooperation and expertise of INPE and the Met Office.