The Emission of Corona from Falling Drops

[摘要] Measurements have been made of the pressure dependence of the electric field strength Fo required to initiate corona from water drops of spherical radius R and charge Q falling between electrodes at a velocity of about 4.5m.sec-1. At a pressure p of 1000 millibars in a positive vertical field a value of Fc of 9.0±0.5kV/cm was required to produce charging of the drops, whereas for p=500 millibars the critical value of Fc was reduced to 5.5±1.0kV/cm. In the presence of a horizontal electric field the critical values of Fo at 1000 and 500 millibars were 6.3±0.3 and 6.9±0.3kV/cm respectively. Equations are developed, based principally on the work of Dawson (1969) and Richards and Dawson (1971), which explain these results and predict that the maximum fields that can exist inside the regions of thunderclouds containing large raindrops will be independent of p at around 12/R0.3e.s.u., corresponding to about 500kV/m. It is suggested that when such fields have been produced inside thundeclouds the emission of corona from disrupting drops will trigger the lightning discharge.

[学科分类] 大气科学