| Winter storms affect all Canadians and many of their impacts are associated with precipitation. This precipitation can occur as rain, snow, freezing rain or ice pellets. Some research has been conducted on all of these types of precipitation but the least attention has been paid to ice pellets. The atmospheric environment conducive to ice pellets is known in general but the detailed nature of the actual particles is not.; To begin to address this issue, a high resolution digital camera was used to photograph ice pellets for 4 hours during a winter storm at Mirabel, Quebec in November 2003. A total of 1023 images were analyzed to determine the morphology, shapes, and size distributions of the ice pellets. Some ice pellets were opaque, others were clear, and some had bands of varying opacity. At most, 7% of the particles were spherical. Many particles exhibited bulges, fractures, and spicules. The occurrence of such features suggests that much or all of the initial freezing occurred on the surface as opposed to the drop interior. Approximately 9% of the particles observed were aggregates of 2-5 smaller particles. The ice pellets ranged up to 5 mm in diameter for aggregate particles and up to 3 mm in diameter for individual particles. The average diameter of all particles was 1 mm. A range of different particle characteristics were observed to be occurring simultaneously throughout the storm. Collectively, such observations as well as process model results imply that different freezing mechanisms were occurring simultaneously, and that collisions between semi-frozen ice pellets must have been occurring to produce aggregates. |
