Antonio C. V. Saraiva

High-speed video and electromagnetic analysis of two natural bipolar cloud-to-ground lightning flashes

High-speed video records of two bipolar cloud-to-ground flashes were analyzed in detail. They both began with a single positive return stroke that was followed by more than one subsequent weak negative stroke. Due to the elevated cloud base height of its parent thunderstorm, the preparatory processes of each subsequent negative stroke were documented optically below cloud base. In the first event (Case 1) it was observed that all four subsequent negative strokes were initiated by recoil leaders that retraced one horizontal channel segment previously ionized by the positive leader. Those recoil leaders connected to the original vertical channel segment and propagated toward ground, producing four subsequent strokes that had the same ground contact point as the original positive discharge. The second event (Case 2), in contrast, presented 15 subsequent strokes that were initiated by recoil leaders that did not reach the original channel of the positive stroke. They diverged vertically toward ground, making contact approximately 11 km away from the original positive strike point. These results constitute the first optical evidence that both single- and multiple-channel bipolar flashes occur as a consequence of recoil leader activity in the branches of the initial positive return stroke. For both events their total channel length increased continuously at a rate of the order of 104 m s−1, comparable to speeds reported for typical positive leaders.

Characterization of lightning observed by multiple high-speed cameras

This study aims to analyze the visible parameters of the cloud-to-ground discharges such as the average multiplicity, continuing current duration and interstroke interval. Several authors already analyzed these parameters for groups of thunderstorms in some regions. Although some authors did not find differences between those characteristics between different regions, there has not been a comprehensive amount of lightning recordings from the same thunderstorm, in order to evaluate such parameters in a storm-to-storm basis. The lightning data for this work was obtained by four high-speed cameras (Phantom v9.1) set to record 2500 frames per second. They were located in Sao Jose dos Campos, Brazil, as part of the project RAMMER (Automated Multi-Camera Network for Monitoring and Study of Lightning Flashes). Five thunderstorm days were selected for this study and some of the data were recorded manually, which provided a higher number of confirmed cloud-to-ground lightning records. A total of 357 flashes were recorded. As far as the authors know, this is the first time that four high-speed cameras are looking to the same thunderstorm from different locations. Because of the number of cameras and their positions, the coverage area is larger, thereby increasing the number of flashes recorded from the same thunderstorm. These samples allow a more representative analysis of the lightning parameters mentioned above.

A new tool to avoid lightning tragedies like in Praia Grande in December 2014

In 29 December 2014 four people were killed by lightning in Praia Grande beach, state of São Paulo, in the Southeast region of Brazil. This was the second largest number of fatalities due to a single lightning in the Brazilian history. In less than 30 minutes, 16 cloud-to-ground flashes occur in a distance less than 5 km from the location of the fatality, detected by the Brazilian Lightning Detection Network (BrasilDAT), in association with a thunderstorm related to a cold front. The article describes a new computational tool to predict the occurrence of this kind of thunderstorm, giving a forecast with great anticipation and large precision that can be used to provide prior alert for the population.

Lightning forecasting using WRF model over EDP distribution companies areas

The lightning forecasting method called Potential Lightning Region (PLR) is a tool that provides the probability of the occurrence of lightning over a region of interest. The definition of the PLR was based on a combination of meteorological variables obtained from high-resolution Weather Research and Forecasting (WRF) model simulations during the summer season in southeastern Brazil. The model parameters used in the PLR calculation were: most unstable Convective Available Potential Energy (mCAPE), K-Index (KI), Total Totals Index (ITT), 700-500 hPa lapse rate of equivalent potential temperature, vertical velocity averaged between 850 hPa and 700 hPa, and ice-mixing ratio integrated from 700 hPa to 500 hPa. Since 2010, a partnership between the Group EDP-Brasil and the Atmospheric Electricity Group (ELAT) of National Institute for Space Research (INPE) is supporting the ClimaGrid Project that aims for developing a new computational system that integrates a wide range of meteorological and environmental variables to the electrical system information, in order to manage the growing impact of climate changes on power systems engineering, and to minimize its effects as well. The PLR has been operational for the first time in the ClimaGrid Project, and, in this study, we present some preliminary results of the PLR campaign during the 2012/2013 summer over EDP distribution companies areas. The thunderstorm case studies discussed here show that PLR works satisfactorily, being a useful tool to help EDP in the maintenance of the power systems.