Airborne measurements of the electric field and the charge precipitation particles in convective clouds: Lower positive charge centres

A comparative analysis of two meteorological situations studied in south west France in Summer 1984 is presented: 6 June when the cloud tops stopped below the -20 C level and most of the precipitation particles were positively charged, and 28 June, when typical thunderclouds reaching the tropopause occurred, and exploration at nearly the same level showed that the majority of the particles carried negative charges. The sign of the charge on precipitation particles is concluded as relative to the altitude of the cloud top, which implies a given temperature for the level at which precipitation is formed. A detailed case study of three passes made on 6 June through a small isolated cumulus cloud is given. Evidence is presented for the association of positive charge centres at low altitude with the presence of strongly charged graupel.