Analysis and modelling of negative downward lightning current curves between 1985 and 1994 at Morro do Cachimbo research station (MG) / Analise e modelagem de curvas de corrente de relampagos negativos descendentes entre 1985 e 1994, na estacao de pesquisa do Morro do Cachimbo - MG

AUTOR(ES)
DATA DE PUBLICAÇÃO

1998

RESUMO

In this thesis is presented an analysis of 22 negative descendent lightning collected in Brazil from 1985 to 1994 in the Morro do Cachimbo research station (43o 58 26 W, 20o 0039 S) of the Companhia Energética de Minas Gerais (CEMIG). The historic evolution of direct discharge measurements and the thecniques involved are summarised. From the comparation of first return strokes with those of another station in Switzerland, it was noted that electric current wave forms are similar in both countries, although the mean peak current in Brazil (40kA) is greater than that in Switzerland (30 kA) and the average instant in which the peak occurs is greater in Brazil (22 ms) than in Switzerland (13 ms). Differences in subsequent strokes were observed too. To explain such differences it was developed an extension of the Borovski model, from which the conductivity of channel-tower-atmosphere-ground sistem was calculated straightly from mean current curves. The values obtained were 1.21 x 10-6 (W.m)-1 (Brazil) and 2.74 x 10-6 (W.m)-1 (Switzerland). The differences in the peak current and conductivity values were explained based on Ohms Law. It was found that the time to peak current is correlated to the time to peak of derivative current with a linear correlation coeficient of about 94%.The mean third return stroke current was found to be stronger than the second and an explanation for that was suggested. Mcomponents recorded at about 200 ms (peak current values ~2kA) had time to peak lower than those obtained after 1 ms in other research stations.

ASSUNTO(S)

morro do cachimbo (mg) relampagos descarga eletrica raios geofisica espacial condutividade corrente eletrica

ACESSO AO ARTIGO

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