Observations within two regions of charge during initial thunderstorm electrification

Airborne electric field measurements in two small thunderstorms in New Mexico show the existence of a narrow region of charge in each storm during the early stage of electrification. In one case a net negative region of charge was observed at about 7 km (‐ 12°C) about 1.5 km below the radar cloud top, when the electric field was only 600 V m −1 , and could be accounted for by total charge of −0–01 C with a maximum net space charge density of −0.15 nCm −3 , assuming spherical symmetry. This region of charge was about 500 m across and appears to have been associated with an updraught‐downdraught transition zone. In the other cloud, a region of net positive charge, also about 500m across, was detected at 7.7 km (‐20°C) about 500 m below the radar cloud top, when the electric field was about 2000 Vm −1 . In both regions of charge, supercooled liquid water and ice particles including graupel were present, and ice particle concentrations, sizes, and collision rates were at a relative maximum, suggesting that the charge generation occurred via a precipitation‐based mechanism.