Análise das características dos relâmpagos na região sudeste do Brasil / Lightning characteristics in southeastern Brazil

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

The first climatological studies of cloud-to-ground (CG) lightning flashes characteristics in Brazil were published at the middle of 90. However, at that time, the lightning detection network used to be composed by only a few sensors, which restricted the analyses to some specific regions. In the beginning of this decade, new studies were published using lightning data provided by a larger network, covering all the southeastern region of Brazil. However, the periods of data are constrained to only a few years. Currently, the establishment of the RINDAT (Integrated National Lightning Detection Network), which covers six states of the country (GO, MG, ES, SP, RJ, PR), makes possible to accomplish, for the first time, a climatological study of the CG lightning flashes characteristics over the southeastern region of Brazil based on a 6-year lightning dataset (1999-2004). However, as the network experienced several changes in its sensor configuration throughout this period, it was required the development of a detection efficiency model (DEM) that could be used to compensate the variations in the overall network detection efficiency, which directly affects the CG lightning data. Moreover, over the last years, several works in literature have reported that the urban areas affect the characteristics of the local CG lightning flashes. Thus, employing air pollution and meteorological data measured by CETESB automatic stations over the São Paulo metropolitan region (RMSP), a more detailed study of its atmospheric environment was performed as an effort to identify which factors (air pollution or thermodynamics) could be acting more effectively at the local CG lightning activity (by increasing the number of CG flashes, and decreasing the percentage of CG positives flashes and the negative peak current). Thereby, this work made three important contributions for the lightning research in Brazil. The first one was the development of a DEM for the RINDAT, which results revealed its potential to support, in the future, studies of the CG lightning flashes characteristics over regions with poor network coverage by correcting the lightning data. However, some new improvements are still necessary so that the DEM can better retrieve the actual distributions of the peak current and can also correct the multiplicity values. The second was the climatological study of the CG lightning flashes over the southeastern region of Brazil, which presented the geographical distribution of the CG lightning activity and its possible correlation with the topography and the meteorological systems. The urban effect over the large cities was also observed by the increase of the local CG lightning activity and the reduction of the percentage of CG positives flashes and the negative peak current. The temporal analyses have shown some particular characteristics of the CG lightning flashes, such as the diurnal and seasonal variation of the peak current and multiplicity, and differences in the diurnal, monthly and annual behavior of the negative and positive CG flashes. Finally, the urban effect analysis over the RMSP revealed that the air pollution and the thermodynamics together could better explain the observations as if they were considered separately. It was then proposed the Urban Effect Theory, which establishes that the thermodynamics remains the basic mechanism for thunderstorm generation. However, for urban environments, when the air pollution reaches a critical level, it starts to control the convection by changing the temperature profiles at the boundary layer.

ASSUNTO(S)

geosÍfica espacial poluição atmosférica cloud-to-ground discharges ilhas de calor Àreas urbanas cities tempestades thunderstorms air pollution raios remote sensors relâmpagos brasil (região sudeste) signal detection lightning space geophysics heat islands brazil (southest region) redes de detecção detection network detecção de sinais sensores remotos

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