Production of Ice Particles in Clouds Due to Aircraft Penetrations

Abstract

Evidence is presented that the passage of an aircraft through supercooled clouds can produce high concentrations of ice particles (> 1000 L?1 at ?8°C in one case). These Aircraft Produced Ice Particles (APIPs) are characterized, initially, both by their high concentration and very uniform size distribution. The ice particles are contained in a cylindrical-like volume of air that is initially oriented along the flight track of the aircraft; the diameter of the cylinder is ?300 m after 5 min of elapsed time. Possible mechanisms for APIPs are discussed. In view of these findings, care must be taken in the interpretation of data on clouds that have been penetrated by aircraft. It seems likely that some previous observations of abnormally high concentrations of ice particles in clouds were due to APIPs. Also, since APIPs mimic some of the effects produced by deliberate artificial seeding, it could complicate the evaluation of cloud seeding experiments.