Revista de Biologia e Ciências da Terra ISSN: 1519-5228 [email protected] Universidade Estadual da Paraíba Brasil

Januário dos Reis, Ruibran; Abreu, João Francisco de Distribution of atmospheric discharges in Revista de Biologia e Ciências da Terra, vol. 10, núm. 2, 2010, pp. 154-160 Universidade Estadual da Paraíba Paraíba, Brasil

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Volume 10 - Número 2 - 2º Semestre 2010

Distribution of atmospheric discharges in Minas Gerais

Ruibran Januário dos Reis1, João Francisco de Abreu2

ABSTRACT The Companhia Energética de Minas Gerais – CEMIG (Energy Company of Minas Gerais) has studied the atmospheric discharge phenomenon and its influence on transmission lines since 1971. Initially, data were gathered from records in notebooks; after that, counters were used; and finally, the source was a survey network of atmospheric discharges data in real time. Collected data for this study comprehend the period from 1989 to 2002, with a total of 15,330,571 atmospheric discharges. The database was generated from information about latitude, longitude and polarity of each atmospheric discharge. The “cinturão” (belt), the region with the highest atmospheric discharges density, located in an east-west direction, has already been found by other researchers, but this study shows the exact position of the nuclei with higher densities.

Keywords: Atmospheric Discharges, GIS, Minas Gerais, Climatology

Distribuição de descargas atmosféricas em Minas Gerais

RESUMO A Companhia Energética de Minas Gerais – CEMIG tem estudado o fenômeno das descargas atmosféricas e sua influência nas linhas de transmissão desde 1971. Inicialmente, os dados eram obtidos de registros em livros de anotações; posteriormente, eram usados contadores; e finalmente, a fonte passou a ser uma rede de levantamento de dados referentes a descargas atmosféricas em tempo real. Os dados coletados para este estudo compreendem o período de 1989 a 2002, num total de 15.330.571 descargas atmosféricas. O banco de dados foi gerado a partir de informações sobre a latitude, a longitude e a polaridade de cada descarga atmosférica. O cinturão, a região com a densidade mais alta de descargas atmosféricas, localizada na direção leste-oeste, já foi analisado por outros pesquisadores, mas este estudo mostra a posição exata dos núcleos com densidades mais latas.

Palavras-chave: Descargas atmosféricas, GIS, Minas Gerais, Climatologia

1. INTRODUCTION qualitative form. Knowledge about the physical properties of those discharges and protection Benjamin Franklin’s experiment in 1750 systems began to come up in 1920s. The opened the doors to the study of atmospheric installation of the first atmospheric discharges discharges. This phenomenon, until then purely Storm Location System – SLT of Latin America explicative, started to take a quantitative form, in Minas Gerais, carried out by Cemig at the because Franklin showed the existence of end of 1988, provided the beginning of a electrical loads in lightning. According to database with information about atmospheric Krider (1999), for more than 170 years the study discharges occurring around the state. For each of atmospheric discharges remained in its atmospheric discharge that occurs, the system

154 provides information about latitude, longitude, 2. BASIC CONSIDERATIONS hour, polarity and intensity, in addition to maintaining a database. The main goal of this In general, one can say the Minas Gerais study is to map the atmospheric discharges relief, characterized by elevated plains, climatology through the analysis of time and depressions and valleys, has resulted from an space data, and also the total average annual alternation of morphoclimatic processes amount of discharges that occurred in Minas activity, sometimes favorable to the formation Gerais; a regional analysis of the atmospheric of large flattening surfaces, and sometimes to discharges polarity is included. linear engraving, with the deepening of water streams (Cetec, 1983). Figure 1 shows, in a 1:50,000 scale map, the average relief of Minas Gerais, a state that has valleys and mountains with elevations ranging from 200 to 2,890 m.

Figure 1 – Minas Gerais altimetric map

This research analyzed only cloud-soil According to Naccarato (2001), the lightning, which is responsible for 70% of non- occurrence of positive frequency can vary and, programmed turnoffs in Cemig’s distribution in some cases, even be superior to the negative and transmission area. This lightning can be one. Reference is made to three factors that positive or negative. According to Uman seem to influence the percentage of positive (1987), negative lightning corresponds to 90% lightning: of the total, in average terms.

155 a) The altitude of positive loads next to the top of the cloud is related to the geographic latitude and to the year’s seasons. The lesser the latitude, the greater the positive center height, which renders difficult the occurrence of positive lightning. The same happens in summer, when the clouds are normally higher. b) The variation of the horizontal wind velocity with the height is directly associated to meteorological conditions. The greater the winds gradient with the height, the greater the positive loads displacement regarding Figure 2 – Grid used for obtaining annual average the negative ones (cloud shearing), which discharges in Minas Gerais. renders it easy for positive lightning to reach the soil. 4. RESULTS c) Storm cloud dissipation. As the rain Figure 3 shows the monthly average eliminates the negative load centers at the distribution of atmospheric discharges in Minas cloud basis, only the positive centers remain Gerais. The months of January, February, in the higher parts. Without the armoring of November and December present the highest negative load centers, the possibility of number of discharges, while February and occurrence of positive lightning toward the November present the highest monthly average soil increases. number of atmospheric discharges. Uman et al. (1989), Berger (1994), Pinto The months between May and Jr et al. (2000), Naccarato (2001) and Mesquita September are the ones with the smallest (2001) describe the sequence of processes that indexes of discharges. involve lightning with negative loads.

3. DEVELOPMENT

Several works have been published with information about atmospheric discharges observed by the SLT, all of them aiming at the elaboration of an atmospheric discharges statistics: Araújo, et al., 1990; Carvalho, et al., 1995; Diniz, et al, 1996; Pinto, et al., 1999; Naccarato, K.P., 2001; Reis, et al. (2001) and Reis, et al. (2001). According to the data collected by the SLT in the period from 1989 to 2000, the Figure 3 – Monthly average atmospheric discharges in establishing of an annual average climatology of Minas Gerais atmospheric discharges in Minas Gerais was investigated. The map of atmospheric discharges Data were collected for a 20 x 20 km density, in Figure 4, was made from the grid in Minas Gerais (Figure 2). calculation of the atmospheric discharges average in all 853 cities of Minas Gerais. Altogether, 15,330,571 atmospheric discharges data that occurred from 1989 to 2002 were used.

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Figure 4 – Comparison between the densities of atmospheric discharges observed by the counters and by SLT

5. ANALYSIS OF THE RESULTS Table 1 - Shows the list of 20 Minas Gerais cities with the highest indexes of atmospheric discharges density Table 1 shows the list of 20 Minas City Density

Gerais cities that present the highest indexes of Ibirité 7.959034 atmospheric discharges density. In Belo Ouro Branco 7.873761

Horizonte, Barreiro borough presents the 7.76088 highest density indexes and Venda Nova region 7.529011 presents the lowest values. 7.374197

Figure 4 shows the relation between Itaverava 7.037172 positive and negative atmospheric discharges in da Noruega 6.977416

Minas Gerais. One observes that 77% of the 6.547065 occurred discharges were negative, while the Sarzedo 6.542627 positive ones correspond to only 23 %. Similar 6.533101 values have also been found by other authors, 6.402351 who studied cases in some of Minas Gerais 6.352518 regions (PINTO e PINTO, O. Jr et al. 1993; São Brás do Suaçuí 6.243161

ODIM et al., 1998; GIN et al., 1999; MENDES Piranga 6.135208 et al., 1998; NACCARRATO, 2001). 6.051948

Santa Rita do Jacutinga 6.037101

Medeiros 6.016643

Ouro Preto 5.994894

Capela Nova 5.961859

Mário Campos 5.957143

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Figure 4 – Relation between atmospheric discharges of positive and negative polarities

Figure 5 shows the relation between Along the “belt” of atmospheric discharges positive and negative discharges by Minas maximum density, the relation between positive Gerais State regions. In the northwest, north and and negative discharges is near the State northeast regions, the positive discharges average value. percentage is lower than the negative one.

Figure 5 – Comparison between the positive and negative polarities in each region of Minas Gerais

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6. CONCLUSION ARAÚJO, R.L. et al. Applied lightning research in an inter-tropical mountainous area. In: I- The different kinds of climate existing in SIDEE – THE FIRST INTERNATIONAL Minas Gerais are due to factors of macro-, CONFERENCE ON POWER meso- and micro-scale origins. The activity of a DISTRIBUTION, Belo Horizonte, Minas South Atlantic semi-stationary anticyclone Gerais, novembro, p.11-14, 1990. defines a semiarid climate in the north and northeast regions of Minas Gerais. The cold AYOADE, J.O. Introdução à climatologia para fronts that reach the State in the SW-NE os trópicos. Difel, 1983, 332p direction are responsible for the beginning of the rainy season, from October to April, and BENETI, C.A. et al. RIDAT – Rede Integrada also for the floods. de Detecção de Descargas Atmosféricas no Altimetry, relief shape and continental Brasil: Situação Atual, Aplicações e dimensions define the wind corridors and space Perspectivas. In: XIII CONGRESSO distribution of the temperature and relative air BRASILEIRO DE METEOROLOGIA, Rio de moisture. So, the orographic and convective Janeiro, 2000. processes come up. They are responsible for the distribution of rain in some months of the year, CARVALHO, A.M. et al. Pesquisa de descargas most of the times together with atmospheric atmosféricas em Minas Gerais – principais discharges. parâmetros aplicáveis à engenharia. In: XIII Although this study was carried out with SNPTEE – SEMINÁRIO NACIONAL DE information collected from sensors in different PRODUÇÃO E TRANSMISSÃO DE situations, it did not influence the final result, ENERGIA ELÉTRICA, Florianópolis, 1995. because the maximum density “belt” is placed inside the covered area of highest precision. DINIZ, J.H., CARVALHO, A.M. e The months of November, December, CHERCHIGLIA, L.C.L. Lightning Research January and February are the ones with the Carried out by Companhia Energética de Minas highest monthly average values of atmospheric Gerais – Brazil. In: 23rd INTERNATIONAL discharges. The rains occurring in the month of CONFERENCE ON LIGHTNING November are due mainly to orographic and PROTECTION (ICLP). Firenze, Italy, convective processes. Occasional cold fronts September 1996. arrive at the State, and their main function is to increase the relative air moisture. MAIA, F.P.G.M. Alguns aspectos dinâmico- The annual average density of climatológicos em Minas Gerais. 1986. atmospheric discharges in some cities of Minas Dissertação (Mestrado) - Universidade Federal Gerais is close to the highest values found in de Viçosa- UFV, 1986. South Africa and Mexico. The discovery of the “belt” of maximum atmospheric discharge had NACCARATO, K.P. Estudo de relâmpagos no already occurred in the past. Nevertheless, Brasil com base na análise de desempenho do according to the volume of information used in sistema de localização de tempestades. 2001. this research, it is possible not only to confirm Dissertação (Mestrado) – Instituto Nacional de its existence, but also to identify isolated nuclei Pesquisas Espaciais - INPE-CGE, 2001. inside the system. PINTO, O. et al. Cloud-to-ground lightning in REFERENCES southeastern Brazil in 1993. Journal of Geophysical Research, v. 104, n. d24, p. 31, 369-379, 1999. ABREU, J.F. and BARROSO, L.C. - Geografia, Modelos de Análise Espacial e GIS. Belo PRATES, J.E. Controles associados à Horizonte: Ed. PUC Minas, 2003. distribuição espacial da precipitação no verão

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