The objective of this study is to detect zones of supercooled drizzle using data from a vertically pointing radar (VPR). This radar was used in the AIRS (Alliance Icing Research Study) experiment held at Mirabel Airport from November 1999 to February 2000. For cases where conditions favor the formation of drizzle drops with a diameter sufficiently large, a second mode with a distinct speed and reflectivity can be separated from that received from snow. That the second mode corresponds to supercooled drizzle is verified by comparing reflectivities and speeds with aircraft data taken during AIRS. For cases without bimodality, regions of icing may be localized by a computation of the mass flux gradient. Accretion of supercooled water on snow (riming) increases both its density and fall speed. Thus, a sudden increase in snow fall speed indicates the presence of supercooled water. A conceptual model describing necessary conditions for the formation of supercooled drizzle is proposed. This model is based on the analysis of a synoptic situation present for two days of intense icing.

Fabry, Frédéric (Supervisor)