Abstract
Abstract. An 8-year climatological analysis (1989–1996) of lightning network data over Belo Horizonte, a large city located in Southeastern Brazil, and nearby surrounding areas has indicated a significant enhancement of approximately 100% in the negative flash density and of 50% in the positive flash density over and downwind of the city, compared with the other adjacent areas. A decrease of 25% in the percentage of positive flashes was also observed over and downwind of the city. No urban effect was evident in the peak current of both negative and positive flashes. These results are in agreement with the recent results obtained by Steiger et al. (2002) for Houston, except that the strength of the effect is twice larger than in Houston. The reason for this difference is not clear. Key words. Meteorology and atmospheric dynamics (atmospheric electricity; convective processes; lightning)
Highlights
Westcott (1995) was the first to reveal the effect of several cities on enhancing cloud-to-ground (CG) lightning activity over and downwind of the cities
Steiger et al (2002) were the first to investigate the urban effect on lightning characteristics, such as the percentage of positive flashes and peak current, based on a 12-year climatological analysis (1989–2000) of the National Lightning De-Correspondence to: I
The contamination by intra-cloud flashes may extend above this threshold, mainly for positive flashes, the above consideration has no influence on the results presented in this paper
Summary
Westcott (1995) was the first to reveal the effect of several cities on enhancing cloud-to-ground (CG) lightning activity over and downwind of the cities. Several recent studies (Orville et al, 2001; Soriano and Pablo, 2002; Steiger et al, 2002; Naccarato et al, 2003) have confirmed this result. They have attributed the effect to the urban heat island circulation, even though a possible role of air pollution has been suggested. Steiger et al (2002) were the first to investigate the urban effect on lightning characteristics, such as the percentage of positive flashes and peak current, based on a 12-year climatological analysis (1989–2000) of the National Lightning De- Several authors have found evidence of urban effects on the local weather phenomena (Myrup, 1969; Braham, 1974; Huff and Changnon, 1973; Semonin and Changnon, 1974; Changnon et al, 1981; Landsberg, 1981; Karl et al, 1988, Balling and Idso, 1989). Steiger et al (2002) were the first to investigate the urban effect on lightning characteristics, such as the percentage of positive flashes and peak current, based on a 12-year climatological analysis (1989–2000) of the National Lightning De-
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