Hydrometeor charges observed below an electrified cloud using a new instrument

Investigation of charges on particles in thunderstorms was conducted during the Severe Thunderstorm Electrification and Precipitation Study. In the case presented here, aircraft measurements of the electric field, and hydrometeor size and charge, were made in a precipitation shaft beneath the base of a small convective cloud which was electrified, but which produced no lightning. A newly designed instrument was used to obtain particle image and charge measurements for particles larger than 0.2 mm in size. Laboratory tests and calculations suggest that under optimum conditions particle charge can be determined with this instrument to within 13% for particles carrying more than a few pC of charge. Uncertainty in charge magnitude increases to 24% in less optimum conditions. It was found in this shower of melting graupel with a peak concentration of similar to 80 particles m(-3) that 70% of the particles were charged, with 98% of the charged particles having positive charge. Peak particle sizes were 2 mm, and peak charges were 25 pC. The magnitude of charge varied widely for particles of a given size, but minimum, average, and maximum charge generally increased as particle size increased. The hydrometeors in this region constituted a lower positive charge center. This center must have developed through microphysical interactions and not charge transferred by lightning discharges.