Estimating icing amounts caused by freezing precipitation in Canada

Abstract

The Chaine and Skeates icing model is a semi-empirical model. It is based on the formulations proposed by McKay and Thompson (1969). Horizontal ice accretion thickness is assumed to be the observed precipitation amount adjusted by the appropriate ice density. Clear ice density is assumed to be 900 kg/m 3. Vertical ice accretion thickness is proportional to precipitation rate and wind speed. Ice accretion occurs only at temperatures near or below freezing. All impinging water is assumed to turn into ice. The freezing fraction is assumed to be one. Horizontal and vertical ice thicknesses are changed into equivalent radial thickness (Chaine and Castonguay, 1974). All parameters used in this model can be derived from routinely observed meteorological data. Icing amounts estimated by this model are very sensitive to wind speed and precipitation rate. Model simulated 30-year return period equivalent radial ice amounts for 20 Quebec locations are compared with collocated Passive Ice Meter data and the results are found to be reasonable. The variation of ice amount with height can be estimated by a log function proportional to 10 m icing amounts, except in British Columbia. Also the 30-year return period equivalent radial ice estimates due to freezing precipitations for 303 locations in Canada are calculated and an Ice Map is plotted. In the future, more work needs to be done to estimate ice amounts due to other forms of icing such as in-cloud rime icing and wet snow. These quantities should be added to the current amounts to make the ice map complete. Anecdotal ice information should be collected to validate the map.