Diagrams of Ice Growth Environments Designed for Educational Use

A web search for “ice habit diagram” will return figures from textbooks and papers that have substantive differences. Contributing to the differences among diagrams is inconsistent terminology and in some cases older source materials that were subsequently shown to contain errors. To fill this gap in educational materials on ice microphysics for students, we have designed simplified diagrams adapted from specialist ice habit figures and terminology in previous work. The revisualized diagrams emphasize the relatively small number of ice growth forms by vapor deposition arising directly from the underlying surface processes by which mass is added to a crystal – tabular, columnar, branched, side-branched, tabular polycrystalline and columnar polycrystalline – and where these growth forms occur as a function of air temperature and relative humidity with respect to water. In contrast to categorization of final particle shape, the concept of ice growth form uniquely connects regions of the diagram to the physical pathways by which an ice crystal grows. Key processes that are simple to visualize with the refined diagrams include that branched and side branched growth responsible for dendrites only occur in environments with RHwater >= 100% and that myriad shapes of observed ice particles are often the result of a sequence of growth forms that occur as the particle traverses different temperature and humidity environments as it falls. We showcase applications of the diagram to identify sequences of environmental conditions and physical processes (such as vertical motion or ventilation) experienced by individual particles using examples of very high-resolution Particle Habit Imaging and Polar Scattering (PHIPS) imagery from winter storms sampled during the NASA Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) field campaign. Open source software to tailor the diagrams for a user’s specific needs includes options to plot the information in terms of relative humidity with respect to ice and vapor density excess.