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. The ambient temperature and the average graupel temperature are presented as an alternative pair of variables describing the charge transferred between ice particles during a collision. These variables are alternative to the generally used air temperature and liquid water content. A new charging diagram is also presented here. The results suggest that 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 spheres 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. The target temperature was adjusted with a Peltier element keeping the target always equal or above than the ambient temperature. The implications of these results to the thunderstorm electrification are discussed.