How much lightning strikes the ground?
Lightning is unpredictable but, on average, lightning strikes within a cloud outnumber lightning strikes from the cloud to the ground. The relative likelihood of these two types of lightning is known to vary with latitude but the precise reasons for this variation are not completely understood. Now Colin Price and David Rind of the NASA Goddard Institute for Space Studies, New York, have proposed that the fraction of lightning striking within the cloud increases with the depth of the sub-freezing part of the thunderstorm (Geophys. Res. Lett. (1993) 20 463).
