The Ratio of Cloud to Cloud-Ground Lightning Flashes in Thunderstorms

Abstract

Observations of the ratio of cloud to cloud-ground lightning flashes in thunderstorms have been reviewed, and used to obtain empirical relationships between this ratio (z), latitude (?) and annual thunder-days (T). The 29 observations, covering a latitude range 69°N to 37°S, gave a mean value of z of 3.35. The empirical relationship proposed between z and ? is z(?) = 4.16 + 2.16 cos3?, 0 ≤ ? ≤ 60°. From 26 pairs of values of z and T, covering the range 5 to 81 thunderdays per year, the proposed relationship is z(T) = 1.0 + 0.063T, 10 ≤ T ≤ 84 z = 6.3, T > 84. Information on z for high latitudes is sparse. It is probable that z lies between 1 and 2 for ? > 60° and T < 10. The existence of a relationship between z and T is attributed to the fact that both are related to latitude. The relationship between z and ? probably depends on the variation of freezing level height with latitude, and a possible relationship between z and freezing level height is examined. Where both ? and T are known, the proposed estimate of z for ? up to 60° and T up to 84 is z(?T = (4.16 + 2.16 cos3?)[0.6 + 0.4T/(72 ? 0.98?)].