Because of the destructive potential of hailstones, the likelihood of hail formation is an important component of forecasting severe weather. While meteorologists have a good knowledge of the growth characteristics of hailstones, the factors determining whether a particular thunderstorm will produce hail or not are not well understood. Hailstones are roundish in shape, with lobes or proturberances on the surface. The cross section exhibit an onion-type layered structure with alternating opaque and clear layers caused by the presence of more or less numerous air bubbles. The air bubble and crystallographic characteristics reflect the environmental conditions under which the hailstones are formed. Some relationships between hailstone structures and growth environments have been found, with additional clues to be uncovered. Under this grant, Dr. Pflaum will examine the air bubble and crystallographic properties of frozen, soaked rime grown in the laboratory with varied temperature and pressure. A detailed knowledge of the relationship will lead to a better interpretation of growth environments when decoding hailstone structures. The experiments will be conducted at the cloud physics laboratory at the University of Toronto.
