Laboratory experiments on the effect of organic acids and metals on the charge transfer during ice crystal – graupel collision under the conditions similar to stratiform clouds

Abstract. Laboratory investigations have been carried out to find the sign and magnitude of charge transfer during the collision between ice crystals and graupel in the presence of supercooled water droplets inside the cylindrical steel chamber kept inside a walk-in cold room, which can reach a temperature of −30 °C. The experiments were performed with pure water (Milli-Q, 18.2 Megohms-cm) and with trace amounts of organic acids and metals at low Rime Accretion Rate (<0.40 g m⁻² s^-1) applicable to stratiform clouds in the temperature range −5 to −27 °C. The ice crystals and supercooled droplets collided with the graupel target at a constant impact velocity of 2.2 m/s. The presence of trace chemicals (organics or metals) saw significant increase in the magnitude of charge transferred per crystal collision to the graupel. These experiments therefore suggest that the presence of trace amounts of organics or metals in cloud water can significantly alter the electrical structure of stratiform clouds.