Cloud Condensation Nuclei (CCN) in Freezing Drizzle

Nevada System Of Higher Education, Desert Research Institute, Reno NV

Investigators

Abstract

This grant supports the participation of Dr. Hudson in the AIRS II project (second Alliance Icing Research Study), a collaboration of American, Canadian, and European agencies and institutions motivated by the practical problem of aircraft icing. The AIRS field program is scheduled for the winter of 2003-04 and based at Mirabel Airport, north of Montreal, Canada, where a surface observing network and ground-based remote-sensing equipment will be located. Dr. Hudson and his colleagues will be responsible for cloud microphysical observations aboard the NSF C-130 aircraft operating out of Cleveland, Ohio. The main scientific objective is to explain the circumstances by which regions of supercooled cloud can form and continue to exist though ice crystals may also be present. The C-130 will be equipped for measuring the water content and ice content of clouds; the concentration, size, habit, and density of ice crystals; the concentration of ice-forming nuclei; and the concentration and characteristics of aerosol particles both within the project area and in the air upstream of where the clouds form. Dr. Hudson will operate his CCN (cloud condensation nuclei) spectrometers to give information on the nucleating ability of aerosol particles in and around the clouds of interest. Attention will be focused on the large nuclei that are active at low values of supersaturation. These are the particles that quickly grow to sizes large enough to promote coalescence and the formation of drizzle-size drops, which are a major cause of aircraft icing. CCN are a critical link in the sequence of events leading from aerosols in the clear air, to the formation of cloud droplets, to the generation of either ice crystals or raindrops. The research contributes not only to the fundamental understanding of microphysical processes in supercooled clouds but also to the advancement of aviation safety.