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 (λ) 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 λ is
zλλλ
From 26 pairs of values of z and T, covering the range 5 to 81 thunderdays per year, the proposed relationship is
zTTT
zT
Information on z for high latitudes is sparse. It is probable that z lies between 1 and 2 for λ > 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 λ 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 λ and T are known, the proposed estimate of z for λ up to 60° and T up to 84 is
zλTλTλ
