Guillermo G. Aguirre Varela

Temperature Dependence of Static Charging in Ice Growing by Riming

Abstract Charge transfer between colliding ice particles is measured using a wind tunnel inside a cold room. A cylinder growing by riming in a wind tunnel was used as a target for collisions between 5 and 6 m s−1 with ice spheres of 100-µm diameter. The target temperature was adjusted to simulate different liquid water concentrations. As the target temperature increased, for air temperatures below −18°C, initial positive target charging reversed sign to negative; with a further temperature increase the charging reversed sign again. These measurements, which are relevant to thunderstorm electrification, were carried out with and without riming and results are compared with other works. A novel approach is presented here suggesting a new pair of variables describing the charging.

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 μm in diameter; the velocity was between 5 and 6 m s−1. The ambient temperature was between −8° and −24°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.