A Quantitative Assessment of Precipitation Mechanisms of Thunderstorm Electrification

[摘要] Calculations based on both the Marshall-Palmer distribution equation and the concentrations of solid and liquid hydrometeors compiled by Sartor (1967), have been made of the contributions made by precipitation particles of different sizes to the charging rate, the maximum volume charge density on precipitation and the precipitation current produced within a cloud when a precipitation mechanism of electrification is operating.It was found that at all stages during the growth of the cloud the dimensions of the precipitation particles which provide the major contribution to the electrification are small. For a precipitation rate of 10 mm hr-1 the primary contribution is made by particles of less than 0.1 cm diameter and even in immensely active clouds with a precipitation rate of 200 mm hr-1 the optimum diameter is below 0.2 cm. On the other hand, the diameter of precipitation particles which provide the major contribution to the radar echo intensity increases from 0.25 to 0.42 cm as the precipitation rate increases from 10 to 200 mm hr-1.Calculations showed that the values of precipitation current and volume charge density which several workers have shown to be essential requirements of a tenable theory of thunderstorm electrification can be achieved by a precipitation mechanism operating with a precipitation rate of only about 15 mm hr-1, which corresponds to a precipitation water content of around 0.8 gm m-3.

[学科分类] 大气科学