Evaluation of the Performance Characteristics of the North American Lightning Detection Network Based on Tall-Structure Lightning

Abstract

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.

FDTD analysis of lightning electromagnetic pulses considering topography and presence of grounded strike object

“…The correction factor, which is defined as the ratio of a field-to-current conversion factor for lightning strike to a tall object to that for the corresponding lightning strike to flat ground (given as 2cd/v for magnetic field, where d is the distance between lightning strike and observation points), derived for the 553-m CN Tower for case (b) is given as f tall_top =[1+ bot (1+ top )] v/(v+c), where  bot is the current reflection coefficient at the bottom of the tall object,  top is the current reflection coefficient at the top of the tall object for upward-propagating waves, v is the return-stroke wavefront speed, and c is the speed of light. For  bot =0.9,  top =-0.67 (these correspond to the lightning-channel equivalent impedance of 1000  and the tall-object characteristic impedance of 200 ), and v=c/3, the correction factor is f tall_top =0.32, which is close to the observed ratio (0.38 on average) of the peak current measured directly near the tower top and corresponding NALDN-reported peak current [2].…”

Overview of Recent Progress in Lightning Research and Lightning Protection

“…Performance characteristics of the NALDN have been recently evaluated using rocket-triggered lightning [17], [18], video recordings [88], and instrumented towers [83].…”

On validation of FCCFs for lightning striking tall objects considering propagation effect of finitely conducting earth

“…The returnstroke discharging current I SC (h,t) includes two components-a breakdown current and a corona current. Each of the two components is calculated by using the analytical expression suggested in [43] as below, 12 …”