COMPUTED CONDITIONS OF CORONA EMISSION FROM RAINDROPS

The altitude of corona emission from charged raindrops located in a ve rtical ambient electric field is calculated by coupling the corona exp erimental results obtained by Dawson (1969) with the raindrop model of Coquillat and Chauzy (1993). This model provides the drop shape and e lectric surface field necessary to calculate the corona occurrence alt itude from a fitting of Dawson's data. The original results are presen ted in the form of vertical profiles of the critical field, which is t he ambient field that causes disruption or a corona. These results arc directly comparable with in situ measurements of electric field, rain drop size, and net charge. If we make the assumption that positive str eamer propagation is of prime importance for lightning initiation, the critical field profiles allow us to determine the minimum net charge of a drop which could initiate a discharge in a given ambient field.