Lightning And Precipitation: The Possible Electrical Modification Of Observed Raindrop Size Distributions

Many studies of cloud electrification have suggested that the presence of precipitation in the mixed phase region of the cloud is essential for charge separation and lightning initiation in clouds. However, observations of the rain gush phenomenon, a transient amplification in near-surface intensity after an overhead lightning also suggest that the lightning discharge can substantially enhance precipitation intensity at the ground. But the microphysical link between lightning and enhanced precipitation intensity after lightning is not well understood. With the observation of a transient amplification in the rain intensity and broadening of the corresponding Raindrop Size distribution (RDSD) after the lightning, it is inferred here that the lightning-induced atmospheric ions and prevailing electrical forces may potentially modulate the RDSD as well as the rain intensity by influencing the collision-coalescence process and the growth rate of raindrops after lightning. The time delay between the lightning and subsequent increase in rain intensity at the Earth's surface was observed to be between 2-4 min. Also, a good correlation was observed between the variations in lightning frequency and the rain intensity during thunderstorms with an average time lag of 4 min. Piepgrass et al. (1982) have reported a good correlation between lightning frequency and rainfall when the precipitation lagged the lightning by times of 4 and 9 min. These observations indicate that the association between lightning frequency and rainfall with 4-min time lag (the shorter one) may be a result of the lightning-induced growth of raindrops below the melting layer rather than the enhancement in precipitation in the mixed phase region of cloud. The new knowledge, coupled with our related work (MUDIAR et al., 2018) on stratiform clouds provides a compelling basis for the parameterization of the electrical processes in weather/climate models.