Ice particle habits in Arctic clouds

Ice crystals in atmospheric clouds have shapes, which affect their density, terminal fall velocity, growth rate and radiative properties. In calculations for climate change predictions, weather forecasting of precipitation, and remote sensing retrievals, idealized crystal shapes uch as columns, needles, plates and dendrites are assumed. Using new technology imaging instrumentation with a resolution of 2.3 gm, recent observations in Arctic clouds have shown that such pristine habits only describe approximately 3% of the particles. The measurements were made from an aircraft during April 1998 and cover atemperature range of 0 øC to -45 øC. Boundary layer, multi-layer and cirrus clouds were examined. The commonly observed irregularly shaped particles either consisted offaceted polycrystalline particles or sublimating (solid to vapor) ice particles with smooth curving sides and edges. Since climate warming is now predicted to be largest in the Arctic, and cloud properties significantly affect the radiation balance, it will be necessary toconsider the effects of non-pristine ice particle habits in such calculations and predictions.