CHARGING IN ICE-ICE COLLISIONS AS A FUNCTION OF THE AMBIENT-TEMPERATURE AND THE LARGER PARTICLE AVERAGE TEMPERATURE

Measurements of charge transfer between ice particles are reported. Th e ambient temperature and the average graupel temperature are presente d as an alternative pair of variables describing the charge transferre d between ice particles during a collision. These variables are altern ative to the generally used air temperature and liquid water content. A new charging diagram is also presented here. The results suggest tha t other variables would be necessary to better describe the phenomena. Some of the current hypotheses on charge transfer are also discussed. The data gathered in the present experiment correspond to collisions made in a wind tunnel between a cylinder growing by riming and ice sph eres of 100 mu m in diameter; the velocity was between 5 and 6 m s(-1) . The ambient temperature was between -8 degrees and -24 degrees C. Th e target temperature was adjusted with a Peltier element keeping the t arget always equal or above than the ambient temperature. The implicat ions of these results to the thunderstorm electrification are discusse d.