Contact Versus Immersion Freezing of Freely Suspended Droplets by Bacterial Ice Nuclei

Abstract

Droplets freely suspended in the air stream of a wind tunnel were nucleated with dedicated bacterial cells in either the contact or immersion mode. Immersion freezing seemed to give a noncontinuous frequency distribution of freezing with temperature whereas the corresponding curve for contact was monotonic. Although the latter nucleation mode was more efficient by ?2°C, the temperature ranges over which droplets froze by either mode of nucleation were closer to 0°C than those so far published for nonbiogenic ice nuclei of natural origin.