Supercooled large drops (SLD) associated with freezing precipitation (FP) represent a critical hazard to aircraft flight operations. Thus, it is crucial to forecast whether clouds are composed of innocuous ice crystals or the dangerous SLD. It is well known that the icing intensity within a supercooled cloud is related both to the supercooled liquid water content (SLWC) and to the mean volume diameter (MVD) of the droplet population (Newton, 1978: J. Aircraft, 15, 374). Recently, a relatively sophisticated cloud physics package has been formulated (Tremblay et al., 1996: Tellus, 48A, 483) for numerical weather prediction models. However, in this package as in other current mixed phase cloud schemes, only the SLWC can be inferred and no information about the MVD can be obtained. Thus, icing intensity forecasts are still a challenge. In addition, even if a high resolution nested model capable of simulating cloud scales (e.g., the Canadian MC2) is available, no microphysical modeling study has been attempted for scheme validation or to study conditions favorable to the formation of SLD. Aircraft data collected during the Canadian Freezing Drizzle Experiments (Isaac et al., 1998: AMS Conf. Cloud Phys., Everett, Wash.) in areas where freezing rain and freezing drizzle are the most common in North America (Newfoundland, 1995 and Ottawa. 1996/97 and 1997/98) provide a unique database for modeling studies and validation.
The objectives of this work are to use the Canadian Freezing Drizzle Experiment research aircraft data to evaluate the ability of the mixed-phase cloud scheme of Tremblay et al.(1996) to forecast the presence of supercooled water and to study the possibility of improving the scheme in order to provide some useful information on the MVD of the droplet population.
The 8th Conference on Aviation, Range, and Aerospace Meteorology