THUNDERCLOUD ELECTRIC FIELD SOUNDINGS WITH INSTRUMENTED FREE BALLOONS
WEBER, MARK EDWARD
Doctor of Philosophy thesis
A Balloon Electric Field Sensor, released into a thunderstorm at Langmuir Laboratory on 12 August 1976, measured the electric vector and wind profile along its track. During a major portion of its ascent, the instrument was in an intense updraft. We infer a maximum vertical wind component of about 15m/s. Horizontal flow, at 10-15m/s towards the northeast, was encountered above 7000m (msl). The behavior of the electric vector indicated that the balloon rose through an 800m thick region of positive charge in the lower portion of the cloud. Above this, negative charge extended from 5200m to 8200m (msl). We imputed intense horizontal electric field components to a volume of negative charge, situated near 6700m (msl) in a region where the rainfall rate was only about 3mm/hr. Lightning subsequently discharged this volume. The cloud contained positive charge above 8200m; however, an increase in the electric field's magnitude after a lightning flash probably resulted from a nearby negative distribution, close to the radar echo top. Electrical corona, induced in pointed rods affixed to a radiosonde, was measured as the sonde rose through a thundercloud on 21 July 1978. The storm's most vigorous activity was well to the south of Langmuir Lab. Although our instrument was carried 6000m in this direction, it did not reach the region of heaviest precipitation. The corona record indicates that strong fields and charge of both polarities were encountered during the ascent. An abrupt decline in upwards directed corona current as the instrument passed through the cloud's upper surface may have resulted from a negative screening layer.