Calculating lightning strike distance

Lightning strike distance

Return stroke current magnitude and strike distance (length of the last stepped leader) are interrelated. A number of equations have been proposed for determining the striking distance.

The principal ones are as follows:

1. S = 2 x I + 30(1−e ^{− I / 6.8}) –  Darveniza (1975)
2. S = 10 x I^0.65 – Love (1987; 1993)
3. S = 9.4 x I^2/3 – Whitehead (1974)
4. S = 8 x I^0.65 – IEEE (1985)
5. S = 3.3 x I^0.78 – Suzuki (1981)

where:

S is the strike distance in meters
I is the return stroke current in kiloamperes

It may be disconcerting to note that the above equations vary by as much as a factor of 2:1. However, lightning investigators now tend to favor the shorter strike distances given by Equation 4.

Anderson, for example, who adopted Equation 2 in the 1975 edition of the Transmission Line Reference Book (1987), now feels that Equation 4 is more accurate.

Mousa (1988) also supports this form of the equation. The equation may also be stated as follows:

I = 0.041 x S^1.54