Laboratory study of thunderstorm electrification

ELDO E. AVILA; CLIVE P. R. SAUNDERS; NESVIT E. CASTELLANO; HOLLY BAX-NORMAN

Belo Horizonte - Brazil

Conferencia; International Conference on Grounding and Earthing & 1st International Conference on Lightning Physics and Effects; 2004

Title: Laboratory study of thunderstorm electrificationAbstract: Laboratory measurements of the charge transfer separated in rebounding collisions between ice crystals and a graupel pellet growing by riming are analyzed by using a cloud particle imager (CPI). In some of these experiments, the usual negative charging regime noted at low cloud temperatures and moderate water contents is reversed to positive at the end of the measurements when the crystals have grown further. The experiments were performed with an impact velocity of 5.5 m/s, the ambient temperature was varied in the range -15 to -26oC with an effective water content up to 3 g/m3. The CPI shows a clear correlation between the charge sign reversal and the presence of a high proportion of large ice particles or aggregates in the cloud. The results suggest that in collisions between graupel and snowflakes the graupel will charge positively. These are the first measurements of this kind of collision and the findings may have important implications in the thunderstorm electrification process