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[1] The interaction of lightning with the 553-m high CN Tower in Toronto is modeled using the antenna theory model. A simple lossless wire structure is used to represent the tower. The return-stroke channel is modeled as a lossy vertical antenna attached to the tower top. The lossy antenna and the wire structure representing the tower are assumed to be fed at their junction point by a voltage source. The voltage waveform of this source is selected so that the source current resembles a typical lightning current waveform not influenced by the presence of the tall strike object. An electric field integral equation in the time domain is employed to calculate the lightning return stroke current distribution along the CN Tower and along the lightning channel. The equation is solved numerically using the method of moments. The lightning current flowing in the tower at the 474-m level above ground, predicted by the antenna theory (AT) model, compares favorably with the measurements conducted at the CN Tower. Once the temporal and spatial distributions of the current along the tower and along the lightning channel are determined, the corresponding remote electromagnetic fields are computed. Waveshapes of modelpredicted electric and magnetic fields at a distance of 2 km from the tower are in good agreement with measurements. The contribution of the tower to the electric and magnetic fields at 2 km is about four to five times the contribution of the lightning channel.

[1] In this paper, simultaneous GPS time-stamped measurements of the electric and magnetic fields at three distances and of the return stroke current associated with lightning strikes to the Toronto CN Tower (553 m) during the summer of 2005 are presented. The lightning return stroke current was measured using a Rogowski coil installed at a height of 474 m above ground level (AGL). The vertical component of the electric field and the azimuthal component of the magnetic field were measured simultaneously at distances of 2.0 km, 16.8 km, and 50.9 km from the CN Tower. The propagation path from the CN Tower to the first two stations (2.0 and 16.8 km) was along the soil and through the Toronto city, whereas for the third location (50.9 km) the propagation path was nearly entirely across Lake Ontario. The waveforms of the electric and magnetic fields at 16.8 km and 50.9 km exhibit a first zero crossing about 5 ms after the onset of the return stroke. This early zero crossing is part of a narrow undershoot. For fields at 50.9 km the expected zero crossing at about 40 ms is also observed. Metallic beams and other conducting parts in buildings on which electric and magnetic field sensors were located cause an enhancement effect on the measured fields. Although an enhancement can be identified both on the electric and the magnetic fields, the degree of enhancement is actually more significant for the electric field than for the magnetic field. It is shown that the value of the wave impedance (E-field peak to H-field peak ratio) could give an estimate of the enhancement effect of the building on the electric field. Propagation effects (decrease of field amplitude and increase of its risetime) can also be observed in experimental records. It is shown that the fields at 50.9 km are less affected by such attenuation, compared to those at 16.8 km, presumably because the path of propagation is mostly across Lake Ontario. Measured waveforms are compared with theoretical predictions obtained using the five engineering return stroke models extended to include the presence of the strike object, namely, transmission line (TL), modified transmission line (MTLL and MTLE), Bruce-Golde (BG), and traveling current source (TCS) models. A reasonable agreement is found with all five engineering models for the magnetic field waveforms at the three considered distances, although the peak values of the computed fields are systematically about 25% lower than measured values. None of the models was able to reproduce the early zero crossing and the narrow undershoot. As far as the electric field is concerned, larger differences have been observed between simulations and measurements. This may be due to the fact that the enhancement effect of the building on the electric field is stronger than that on the magnetic field. The expression relating current and field peaks associated with strikes to tall structures is also tested JOURNAL

Using Canadian National (CN) Tower lightning data acquired during the summer of 2005, the performance characteristics of the North American Lightning Detection Network (NALDN) were evaluated, including the flash detection efficiency, stroke detection efficiency, absolute location error, location accuracy model error (50%, 90%, and 99% error ellipses), and peak current estimation. The NALDN detected seven out of the seven flashes recorded at the CN tower, resulting in a 100% flash detection efficiency. Furthermore, the NALDN detected 21 out of the 38 return strokes recorded at the tower, resulting in a stroke detection efficiency of 55%. Relative to the CN tower, the NALDN was found to have a median and mean absolute stroke location error of 0.358 and 0.395 km, respectively, for the 21 detected strokes. It was also demonstrated that the NALDN stroke location error seems to have a clear bias towards the north of the CN tower and a slight bias toward the east, with 18 of the 21 strokes predicted to be northeast of the tower. The 50%, 90%, and 99% error ellipses provided by the NALDN were also evaluated. It was found that 71% of the detected strokes (15 out of 21) were enclosed by the 50% error ellipse, 90% of the detected strokes (19 out of 21) were enclosed by the 90% error ellipse, and 95% of the detected strokes (20 out of 21) were enclosed by the 99% error ellipse. The minimum value for the 50% error ellipse axis is set at 0.4 km by Vaisala, Inc., and 20 of the 21 detected strokes had a semimajor axis length of 0.4 km, suggesting that the median location error for strokes hitting the CN tower is 0.4 km or less. The 0.358 km median location error obtained for the 21 detected strokes appears to support this. The dependence of stroke detection efficiency and location error on the characteristics of the current measured at the CN tower is evaluated. The NALDN is found to overestimate the current peak, which is possible to explain for tall-structure lightning. The dependence of stroke detection efficiency and location error on the characteristics of the CN tower lightning-generated electromagnetic pulse, measured 2 km north of the tower, is also evaluated.

Successful simultaneous measurements of significant parameters for lightning strikes to the Canadian National (CN) Tower in Toronto have been performed since the summer of 1991. Three 10‐bit 10‐ns computer‐controlled double‐channel digitizers, with long segmented memory, have simultaneously captured the current derivative at the CN Tower and the corresponding electric and magnetic fields 2.0 km north of the tower. Lightning flashes to the tower were videotaped from two mutually perpendicular directions for the purpose of constructing a three‐dimensional image of the lightning path. Furthermore, the return stroke velocity, a parameter also needed for the analysis of lightning radiation models, has been measured by a computer‐controlled photodiode system. In this paper all relevant parameters for a CN Tower lightning stroke, observed on August 17, 1991, are shown and analyzed.

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