| Abstract |
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An analysis of Canadian Lightning Detection Network (CLDN) data recorded during years 2004 - 2006 is performed for two selected areas in Canada within a 20-km radius around two tall structures: the CN Tower (CNT, 553 m) in Toronto and the Superstack (SS, 380 m) in Sudbury. The explored lightning characteristics include stroke polarity, lake water or land termination (WT or LT), ground stroke densities Ngs, stroke peak currents (including values of I50%, I95%, I5%), distributions of parameters. The results show noticeable differences between characteristics of lightning terminated to lake water and land. In Toronto area (Ngs ˜ 3.24 strokes/(km2·year)), a commonly accepted feature, according to which positive strokes exhibit dominating peak currents in comparison to negative ones, is confirmed only for WT lightning (not close to the CNT), especially in the range of high currents. For LT lightning in the range of current amplitudes close to 50% values, the negative strokes are characterized by larger peaks (by more than 30%) with respect to positive ones. No positive strokes to water were recorded within 5 km near the CNT during the period of analysis. While WT events exhibit a lower Ngs than LT ones, they show larger peak currents. The Sudbury area, characterized by a lower lightning activity (Ngs ˜ 0.91 strokes/(km2·year)), shows the common relation between peak currents of positive and negative polarities (first are dominating). For the SS, the estimated number of upward lightning looks rather low: 0.47 strokes or 0.37 flashes per year. For the CNT, it is about 32 strokes or 14 upward flashes per year. Distributions of Ngs along the distance from the tall objects, beside the increased levels near object, contain dips next to object (up to 3 - 7 km). |