Formation of Ice Crystals and Dissipation of Supercooled Fog by Artificial Nucleation, and Variations of Crystal Habit at Early Growth Stages

Abstract

Abstract The early stages of ice crystal formation in supercooled fogs were studied in detail by electron microscopy, and ice nucleation experiments using liquid propane seeding were conducted in a thermostatically controlled coldroom. Ice crystals, formed by rapid cooling created by the evaporation of liquid propane from a fine nozzle at temperatures from −0.1 to −40°C, were collected and replicated on filmed grids for electron microscope examinations. Most of the ice crystals formed immediately after the liquid propane seedings were spherical (although ∼20% were hexagonal) with diameters ranging from 0.3 to 3 μm and with a mean diameter of 1.5 μm. Electron microscopy revealed a grain boundary in some of the ice crystals. The production rates of ice crystals per gram of liquid propane seeding were measured at temperatures from −0.1 to −20°C. The production rate increased exponentially at temperatures from −0.1 to −4°C, and remained at about 1011 ice crystals per gram of liquid propane seeding at temperat...