Riming electrification mechanism for charge generation within a thundercloud

Abstract

A time dependent model for the rate of growth of the electric field within a thundercloud by the process of graupel formation (riming electrification) has been presented. The parameters of the model are: p 0, the precipitation intensity; q, the charge acquired by the graupel in each collision it makes with an ice crystal and 〈p〉, the charge transfer efficiency. Sets of values for the field growth and the maximum field have been obtained by varying these parameters. It is found that the estimated field for the initiation of a lightning flash (3.4 × 10 5 Vm −1) within a time of about 1200 s can be achieved, taking a reasonable value of q = −1.67 × 10 −14 C only for P 0 ≳ 5.56 × 10 −6 m s −1(20 mm h −1) and 〈 p〉 ≳ 0.5. The maximum attainable electric field, E max , itself is not sensitive to the value of q, within a reasonable range of variation in it (for a given p 0), but its rate of growth is: it grows faster, if g is larger.