Observational Study of Wind Channeling within the St. Lawrence River Valley

Abstract

The presence of orography can lead to thermally and dynamically induced mesoscale wind fields. The phenomenon of channeling refers to the tendency for the winds within a valley to blow more or less parallel to the valley axis for a variety of wind directions above ridge height. Channeling of surface winds has been observed in several regions of the world, including the upper Rhine Valley of Germany, the mountainous terrain near Basel, Switzerland, and the Tennessee and Hudson River Valleys in the United States. The St. Lawrence River valley (SLRV) is a primary topographic feature of eastern Canada, extending in a southwestnortheast direction from Lake Ontario, past Montreal (YUL) and Quebec City (YQB), and terminating in the Gulf of St. Lawrence. In this study the authors examine the long-term surface wind climatology of the SLRV and Lake Champlain Valley (LCV) as represented by hourly surface winds at Montreal, Quebec City, and Burlington, Vermont (BTV). Surface wind channeling is found to be prominent at all three locations with strong bidirectionalities that vary seasonally. To assess the importance of the various channeling mechanisms the authors compared the joint frequency distributions of surface wind directions versus 925-hPa geostrophic wind directions with those obtained from conceptual models. At YUL, downward momentum transport is important for geostrophic wind directions ranging from 2408 to 3408. Pressure-driven channeling is the dominant mechanism producing northeasterly surface winds at YUL. These northeasterlies are most prominent in the winter, spring, and autumn seasons. At YQB, pressure-driven channeling is the dominant physical mechanism producing channeling of surface winds throughout all seasons. Of particular importance, both YUL and YQB exhibit countercurrents whereby the velocity component of the wind within the valley is opposite to the component above the valley. Forced channeling was found to be prominent at BTV, with evidence of diurnal thermal forcing during the summer season. Reasons for the predominance of pressuredriven channeling at YUL and YQB and forced channeling at BTV are discussed.

Perspectives for Very High-Resolution Climate Simulations with Nested Models: Illustration of Potential in Simulating St. Lawrence River Valley Channelling Winds with the Fifth-Generation Canadian Regional Climate Model

“…As reported by [78], this typical situation is observed with approaching warm fronts, when there is a low-level pressure gradient oriented from SW to NE along the valley axis, with the low-pressure located over the Great Lakes and a high-pressure over the Gulf of St. Lawrence. The combination of warm air advection aloft and cold air advection at lower levels leads to a low-level inversion that is favorable to the production of freezing rain in winter and spring.…”

Simulating wind channelling over Frobisher Bay and its interaction with downslope winds during the 7–8 November 2006 wind event

“…Whiteman and Doran (1993), for instance, summarized the mechanisms that produce channelled winds, namely, downward momentum transfer, thermally driven, pressure-driven, and forced channelling. These allowed for the explanation of the highly bidirectional wind regimes in valleys from climatological data available at relatively few locations: Frobisher bay (Nawri and stewart, 2006), The Owens Valley (Zhong et al, 2008), and the st. Lawrence River Valley (Carrera et al, 2009). However, the conceptual models of classic flows induced by topography may have limited skill in describing the complex flow structure and dynamics of the low-level winds resulting from various combinations of three-dimensional topography and meteorological conditions.…”

Evaluating the Ability of CRCM5 to Simulate Mixed Precipitation

“…For example, wind channelling within the SLRV can often lead to intense low-level cold-air advection keeping the surface temperature below freezing when an approaching warm front brings warm-air advection aloft. Previous studies (Carrera et al, 2009;Razy et al, 2012) documented the preponderance of northeasterly to north-northeasterly surface winds during ZR events in the SLRV. The hourly observations of 10 m wind at YUL confirm that during occurrences of ZR winds are, by and large, north-northeasterly and northeasterly (Fig.…”

“…This is an essential step before attempting climate change projections for ZR and IP species. A CRCM5 simulation was performed with a horizontal grid of 0.11°, which has been documented (Lucas-Picher, Laprise, & Winger, 2016) to be essential for good reproduction of local topographic features, such as the SLRV, where the channelling in the valley can maintain or enhance the cold layer near the surface (Carrera, Gyakum, & Lin, 2009;Razy, Milrad, Atallah, & Gyakum, 2012;Roebber & Gyakum, 2003).…”