No abstract

Recent laboratory experiments and in situ observations have produced results in broad agreement with respect to ice crystal habits in the atmosphere. These studies reveal that the ice crystal habit at 2208C is platelike, extending to 2408C, and not columnar as indicated in many habit diagrams found in atmospheric science journals and texts. These diagrams were typically derived decades ago from laboratory studies, some with inherent habit bias, or from combinations of laboratory and in situ observations at the ground, observations that often did not account for habit modification by precipitation from overlying clouds of varying temperatures. Habit predictions from these diagrams often disagreed with in situ observations at temperatures below 2208C. More recent laboratory and in situ studies have achieved a consensus on atmospheric ice crystal habits that differs from the traditional habit diagrams. These newer results can now be combined to give a comprehensive description of ice crystal habits for the atmosphere as a function of temperature and ice supersaturation for temperatures from 08 to 2708C, a description dominated by irregular and imperfect crystals. Cloud particle imager (CPI) habit observations made during the Second Alliance Icing Research Study (AIRS II) and elsewhere corroborate this comprehensive habit description, and a new habit diagram is derived from these results.

A detailed study of mixed‐phase clouds associated with frontal systems obtained from a large dataset collected by the Convair 580 aircraft of the National Research Council (NRC) of Canada is presented. The total length of analysed in‐cloud legs having total‐water content (TWC) >0.01g m−3 was about 44×103km. The ice–water fraction (µ3=ice−water content/TWC) had a minimum in the range 0.1<µ3<0.9, and two maxima for liquid clouds (µ3<0.1) and ice clouds (µ3>0.9). The concentration of particles in glaciated clouds was found to be nearly constant at 2 – 5 cm −3 for temperatures −35°C