LIGHTNING CHARGE ANALYSES IN SMALL CONVECTION AND PRECIPITATION ELECTRIFICATION (CAPE) EXPERIMENT STORMS

A least squares method for analyzing multiple, ground-based measuremen ts of electric field changes produced by lightning has been applied to seven small thunderstorms that occurred on July 19 and August 9, 1991 , during the Convection and Precipitation Electrification (CaPE) exper iment. Two of the storms produced little or no cloud-to-ground (CG) li ghtning, and a third produced CG lightning only during its early stage s. A total of 79 flashes were analyzed on July 19 and 315 on August 9. About 58% of these discharges could be fitted to either a point charg e (Q) or a point dipole (P) model, and in this sample, the spatial pat tern of the Q and P solutions was consistent with a tripole or double dipole charge pattern in the cloud. In cases where there was little or no CG lightning, the inferred region of upper positive charge was qui te close to the inferred negative region. Comparisons of the locations of upper P solutions with measurements of radar reflectivity at S ban d show that the P solutions tended to cluster at altitudes where the r eflectivity was between 25 and 35 dBZ. Comparisons of Q (and P) model solutions with the locations of CG flash strike points, determined usi ng a network of wideband direction finders, showed an average horizont al displacement of 3.9 km with a standard deviation of 3.3 km. This di splacement is consistent with the expected random development of a ste pped-leader channel from the altitude of the negative Q region to the ground.