Characteristics of lightning at tall structures and adjacent areas based on detection network data

Characteristics of lightning occurred at four selected tall structures (heights of 316 to 629 m) and in surrounding areas to ground (for four distance ranges within radius R = 20 km) are determined on the basis of data collected by the North American Lightning Detection Network during 10 years (2000-2009). Two structures are freestanding (CN Tower and Inco Superstack, SS) and two are guyed (CIII TV Tower and KLVY TV mast). Presented results include statistical characteristics on multiplicity, interstroke intervals and stroke peak current values. In general, as often accepted, tall structure (TS) lightning are characterized by somewhat increased multiplicity (e.g., median values of 2 to 3 for negative flashes) than that of flashes in surrounding zones (1.6 to 1.8), but this is not valid for the SS (1.43 vs 1.7 to 1.95) located in the region of low ground flash density (~0.67 flashes/(km
²
·year)). Flashes of high multiplicity (m >10) and even having m larger than at TS are often observed also at remote zones to flat ground and water surface, which was checked also by case studies. Variations of peak current values within one multiple-stroke flash in time and space are addressed. For remote zone of the KVLY (2.3-18 km), the interstroke intervals are characterized by: mode - 60 ms, median value - 86 ms. In analysis of stroke peak current statistical distributions, the EM field enhancement effect of tall structures was taken into account. Estimated peak current values for the events attributed to the TSs are lower (I
_50%
= 3.4 to 13.8 kA) than that of observed negative subsequent events in surrounding areas 2.3-20 km (I
_50%
= 12.9 to 16 kA) and typically not exceeding noticeably the values of the IEEE Standard distribution (I
_50%
= 12 kA). In surrounding areas for negative flashes the difference between currents of first and subsequent strokes is rather small (exception is SS area), and the range for both is I
_50%
≈ 13 to 20 kA.