Impacto da microfísica das tempestades nas características físicas e elétricas dos relâmpagos

Abstract

Brazil has a higher annual (approximately 96 million) incidence of lightning, making the energy, telecommunication sectors and the Brazilian population highly susceptible to the impacts of this phenomenon. The study of lightning and the properties of storm clouds is strategic and of fundamental importance to support the development and improvement of immediate weather forecasting tools. However, there is still a gap in understanding how the microphysical properties of storm clouds impact lightning characteristics (such as type, polarity, size and duration). widely used over the last few decades. In this context, the general objective of the present study is to evaluate the impact of the microphysics of storms on the physical and electrical characteristics of lightning. The storms that are the focus of this research are those that occurred in the Metropolitan Region of São Paulo (RMSP) between November 2011 and March 2012, which were obtained during the CHUVA-Vale do Paraíba campaign. In the first stage of the work, Very Higher Frequency (VHF) sources from the São Paulo Lightning Mapper Array (SPLMA) network and return discharges from the Brazilian Atmospheric Discharge Detection Network (BrasilDAT) were used. With this database, the diurnal cycle of lightning properties was evaluated. The results showed that the highest amount of lightning occurs in the afternoon, approximately from 2 pm to 5 pm local time. Although the frequency of lightning strikes is higher in the afternoon, shorter lightning strikes predominate in this period. It was also observed that the period of the day with the highest occurrence of lightning does not coincide with the period of the day that presents the highest current peaks, indicating that storms caused by late afternoon thermodynamic instability involve less intense lightning in terms of electrical currents. In the second and third stages of the work, the relationship between the microphysical properties and the physical and electrical properties of lightning was examined. Both the duration and the length of the lightning flashes showed a positive relationship with the Eco Top variable of 45 dBZ, that is, the greater the duration/length are large hydrometeors found at greater heights. On the other hand, the area of the lightning showed a higher correlation with the microphysical variables crystal volume and graupel; while the amount of lightning sources was better correlated with the Waldvogel Height. In addition, intracloud and cloud-to-ground lightning are well correlated with Vertically Integrated Ice. In lifecycle terms, storms begin to flash in phase 1 (initiation) of their lifecycle, and increase until they reach their peak in the phase between initiation and maturation. A similar behavior occurred in relation to the number of sources, area and duration of lightning, which increase since the beginning of the storm and reach their maximum in phase 2. After the peak in phase 2 (intermediate time between the first radar echo and maturation), the variables mentioned above decreased during their life cycle until their dissipation. On the other hand, the peak current variable of the BrasilDAT network reached its peak in phase 3 (maturation). Also analyzed in greater detail was a case study of two storms, one with a few lightning strikes and the other with a lot of lightning. This project deepened the knowledge about the impact of microphysics on the properties of lightning and opened opportunities for the improvement of weather forecast models, and as a consequence, it may provide the minimization of damages linked to the negative effects of these storms.