The role of anticylones in replenishing surface cold air and modulating freezing rain duration.

Introduction: Freezing rain (FZRA), a hazardous meteorological phenomenon, is associated with airflows from both cyclones and anticyclones. Though researchers have placed primary emphasis on the cyclone's role in FZRA, we intend to examine the anticyclone's role in transporting near-surface cold air. More specifically, we study its impact on the duration of FZRA in a region of orographically enhanced vulnerability, namely at Quebec City (YQB), located in the St-Lawrence River Valley (SLRV). This region is an active zone of freezing rain due to orographic influences that promote pressure-driven channeling. Methods: Within the SLRV region, we define a severe event using a minimum duration threshold of six hours and found 47 severe freezing rain cases during a 30-year period (1979-2008). We then partitioned these cases into categories based on precipitation phase change and 850hPa geostrophic relative vorticity. Results: We found that the duration of freezing rain is determined in large part by the intensity and location of the anticyclone. Discussion: The anticyclone enhances pressure-driven channeling, and this channeling provides the replenishment of cold air at the surface required to maintain FZRA . Identifying these anticyclonic features provides a novel approach to determine the potential duration of FZRA events. [ABSTRACT FROM AUTHOR]