Atmospheric icing severity: Quantification and mapping

• Atmospheric icing climatology and its severity represented by an icing severity index
• Measurement from two topographically contrasting sites
• Validation based on measurements and reanalysis (NARR)
• Ice accretion based on cylinder model

Atmospheric icing became a primary concern due to the significant impact and hazardous conditions of its accretion on structures. The objective of this study is to provide a map of icing events over 32 years (1979 to 2010) that describes the severity of winter icing. This information will prove useful to prevent damages and economical losses due to icing events by documenting the risk factor.To validate the icing climatology method, two case studies involving two topographically contrasting sites were selected: a simple terrain site which is the airport of Bagotville, near Saguenay (Canada) and a complex terrain site located in Mt Bélair, near Quebec City (Canada). Ice accumulation calculated by the use of reanalysis data was quantified using ice accretion on a cylinder model. Comparison between measurement and the model over Bagotville revealed insignificant differences in ice accumulation less than 0.3 mm, and in duration of icing events less than 0.2 day. On the other hand, during winter months, the calculation that showed a maximum of 60 mm in January 1999 over Mt Bélair site also had an underestimation of ice accumulation that varies from 5 mm to 16 mm. The horizontal resolution of NARR imposes a challenge on the calculation of icing events over complex terrains, especially during the months of November and March when air temperature is near freezing point. Taking into account the liquid water content, the duration of icing events and the classes of icing events as weighting factors, the icing severity index based on reanalysis data was introduced to assess the severity level of icing events, covering the north-east of Quebec including Quebec City, Sept-Iles, the east of Saguenay, the lower St Lawrence River and the Gaspe region. Consequently, an icing severity index mapping that represents the climatology of in-cloud atmospheric icing was produced.