Charge separation in non-riming conditions

LUQUE, M.Y.; BURGESSER, RODRIGO E.; CASTELLANO, NESVIT, E.; AVILA, ELDO E.

OKLAHOMA

Conferencia; XV International Conference on Atmospheric Electricity, 15-20 June 2014, Norman, Oklahoma, U.S.A.; 2014

ICAE

Extensive evidence from aircraft observations in thunderstorms have shown that substantial electriccharge is to be found on millimeter-sized hydrometeors; indicating that the ice phase play an importantrole in the process of charge separation inside the clouds. Electric charge is separated during the contacttime between graupel and ice crystals and then particles with opposite charge could be carried away atdifferent regions of the clouds due to gravitational force and convective currents. This process coulddevelop the different charged regions in clouds.Laboratory measurements have shown that the magnitude and sign of the charge transfer to graupelparticles during interactions with ice crystals is a function of the cloud microphysical conditions. In fact, itdepends on: the cloud temperature, supercooled water concentration, cloud droplet size distribution, icecrystal size and impact velocity.Few experiments were conducted under non riming conditions and under zero liquid water contentbecause the low magnitude of the charging current but ice particles with significant charge is observed instratiform cloud regions where the ambient is subsaturated respect to liquid water.New laboratory measurements of the charge transfer in collisions between vapor-grown ice crystalsand a graupel particle (2 mm diameter) in non-riming conditions are presented in this work. Theexperiments were all performed for a supersaturated-atmosphere with respect to ice and subsaturated withrespect to liquid water; which ensures the environment free of supercooled liquid water droplet. Therelative humidity of the air inside the chamber was controlled and measured during the measurements.The experiments were conducted for ambient temperatures between ?7°C and ?20°C and air velocityaround 3 m/s.