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

2009 ◽  
Vol 48 (11) ◽  
pp. 2341-2361 ◽  
Author(s):  
Marco L. Carrera ◽  
John R. Gyakum ◽  
Charles A. Lin
Keyword(s):  
Surface Wind ◽  
Hudson River ◽  
Geostrophic Wind ◽  
The United States ◽  
River Valley ◽  
Quebec City ◽  
Surface Winds ◽  
Eastern Canada ◽  
St Lawrence River ◽  
Pressure Driven

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 southwest–northeast 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 240° to 340°. 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 pressure-driven channeling at YUL and YQB and forced channeling at BTV are discussed.

scholarly journals Precipitation Modulation by the Saint Lawrence River Valley in Association with Transitioning Tropical Cyclones*

2013 ◽  
Vol 28 (2) ◽  
pp. 331-352 ◽  
Author(s):  
Shawn M. Milrad ◽  
Eyad H. Atallah ◽  
John R. Gyakum
Keyword(s):  
Tropical Cyclones ◽  
Large Scale ◽  
Surface Wind ◽  
Warm Season ◽  
Temperature Inversion ◽  
River Valley ◽  
Eastern Canada ◽  
Near Surface ◽  
The Impact ◽  
Pressure Driven

Abstract The St. Lawrence River valley (SLRV) is an important orographic feature in eastern Canada that can affect surface wind patterns and contribute to locally higher amounts of precipitation. The impact of the SLRV on precipitation distributions associated with transitioning, or transitioned, tropical cyclones that approached the region is assessed. Such cases can result in heavy precipitation during the warm season, as during the transition of Hurricane Ike (2008). Thirty-eight tropical cyclones tracked within 500 km of the SLRV from 1979 to 2011. Utilizing the National Centers for Environmental Prediction (NCEP) North American Regional Reanalysis (NARR), 19 of the 38 cases (group A) had large values of ageostrophic frontogenesis within and parallel to the SLRV, in a region of northeasterly surface winds associated with pressure-driven wind channeling. Using composite and case analyses, results show that the heaviest precipitation is often located within the SLRV, regardless of the location of large-scale forcing for ascent, and is concomitant with ageostrophic frontogenesis. The suggested physical pathway for precipitation modulation in the SLRV is as follows. Valley-induced near-surface ageostrophic frontogenesis is due to pressure-driven wind channeling as a result of the along-valley pressure gradient [typically exceeding 0.4 hPa (100 km)−1] established by the approaching cyclone. Near-surface cold-air advection as a result of the northeasterly pressure-driven channeling results in a temperature inversion, similar to what is observed in cool-season wind-channeling cases. The ageostrophic frontogenesis, acting as a mesoscale ascent-focusing mechanism, helps air parcels to rise above the temperature inversion into a conditionally unstable atmosphere, which results in enhanced precipitation focused along the SLRV.

scholarly journals Forecasting of Surface Winds over Eastern Canada Using the Canadian Offline Land Surface Modeling System

2014 ◽  
Vol 53 (7) ◽  
pp. 1760-1774 ◽  
Author(s):  
Lily Ioannidou ◽  
Wei Yu ◽  
Stéphane Bélair
Keyword(s):  
Land Surface ◽  
Surface Wind ◽  
Multicomponent System ◽  
Small Scale ◽  
Bias Error ◽  
Surface Boundary ◽  
Surface Winds ◽  
Free Atmosphere ◽  
Eastern Canada ◽  
Wind Speeds

AbstractThe capability of the Canadian land surface external modeling system known as the Global Environmental Multiscale Surface (GEM-SURF) system with respect to surface wind predictions is evaluated. Based on the Interactions between Soil, Biosphere, and Atmosphere (ISBA) land surface scheme, and an exponential power law adjusted to the local stability conditions for the prediction of surface winds, the system allows decoupling of surface processes from those of the free atmosphere and enables high resolutions at the surface as dictated by the small-scale heterogeneities of the surface boundary. The simulations are driven by downscaled forecasts from the Regional Deterministic Prediction System, the 15-km Canadian regional operational modeling system. High-resolution, satellite-derived datasets of orography, vegetation, and soil cover are used to depict the surface boundary. The integration domains cover Canada’s eastern provinces at resolutions ranging from that of the driving model to resolutions similar to those of the geophysical datasets. The GEM-SURF predictions outperform those of the driving operational model. Reduction of the standard error and improvement of the model skill is seen as resolution increases, for all wind speeds. Further, the bias error is reduced in association with a rise in the corresponding value of the roughness length. For all examined resolutions GEM-SURF’s predictions are shown to be superior to those obtained through a simple statistical downscaling. In the prospect of the future development of a multicomponent system that provides wind forecasts at levels of wind energy generation, GEM-SURF’s potential for improved scores at the surface and its limited requirements in computer resources make it a suitable surface component of such a system.

A method for determining the frequency of large-magnitude earthquakes using lake sediments

1986 ◽  
Vol 23 (7) ◽  
pp. 930-937 ◽  
Author(s):  
Ronald Doig
Keyword(s):  
Lake Sediments ◽  
Quebec City ◽  
Sedimentation Rates ◽  
Historical Records ◽  
Chemical Analyses ◽  
Large Magnitude ◽  
Eastern Canada ◽  
Deep Layers ◽  
Prehistoric Earthquakes ◽  
St Lawrence River

Eastern Canada has experienced at least five earthquakes of estimated Richter magnitude 6 or greater during the last 350 years. The epicentres are usually under the St. Lawrence River, some 100 km east of Quebec City. Historical records of the earthquake of 1663, possibly the largest of these events, describe high levels of silting in streams for up to several months. A silt horizon in normally organic-rich lake sediments has been found in lakes with separate drainage systems and is interpreted as the 1663 event on the basis of rough sedimentation rates obtained from observation of 137Cs fallout of the 1950's and the effects of a dam on one of the lakes. Two other silt layers correspond reasonably well to the next largest earthquakes of 1791 and 1860 + 1870 (combined). Two deep layers were found that by extrapolation of the assumed 1663 layer yield dates of about A.D. 1060 and 600 and are believed to represent prehistoric earthquakes, though possibly not as large as that in 1663. Chemical analyses of the cores show that organic material, Ti, and especially K are very useful for identifying these layers and others that are not visible in the cores.

scholarly journals The Recent Spread and Potential Distribution of Phragmites australis subsp. australis in Canada

2011 ◽  
Vol 125 (2) ◽  
pp. 95 ◽  
Author(s):  
Paul M. Catling ◽  
Gisèle Mitrow
Keyword(s):  
Nova Scotia ◽  
Phragmites Australis ◽  
Potential Distribution ◽  
Common Reed ◽  
River Valley ◽  
Occurrence Rate ◽  
Quebec City ◽  
Herbarium Specimens ◽  
Rate Of Spread ◽  
St Lawrence River

To provide information on geographic occurrence, rate of spread, and potential distribution of European Common Reed, Phragmites australis subsp. australis, in Canada, we measured 1740 herbarium specimens from 21 collections across Canada, entered the information into a database, and mapped and analyzed these records. The European subspecies australis was first documented in Canada 100 years before it was recognized as an alien invader. It was not until the invading plants had entered a phase of rapid local increase after 1990 that they attracted sufficient attention that a comparison of the invasive and non-invasive plants was made. By 2001, two different races had been distinguished, and soon after they were separated as different subspecies. The first Canadian collection of the alien subsp. australis was made in southwestern Nova Scotia in 1910. By the 1920s, it occurred in southern Nova Scotia, along the St. Lawrence River near Quebec City and at Montreal. The first southwestern Ontario specimen was collected in 1948. Thus by 1950 subsp. australis was known from only four relatively small areas of Canada based on 22 collections. At this same time, the native race, subsp. americanus, had a widespread distribution in Canada represented by 325 collections. This strongly supported the comparable and limited distribution of subsp. australis at the time. By 1970, subsp. australis had spread locally but was still found only in southwestern Nova Scotia, in the St. Lawrence River valley, and in southwestern Ontario. By 1990, subsp. australis had become much more frequent in the St. Lawrence River valley and in southwestern Ontario, and it had extended westward into eastern Ontario. By 2010, it had spread throughout much of southern Ontario and southern Quebec, and it had a more extensive distribution in Atlantic Canada, but the biggest change was its spread into western Canada. It appeared in northern Ontario, northwestern Ontario, southern Manitoba, and interior southern British Columbia. The rate of spread is increasing and within a decade or two, based on the extent of appropriate plant hardiness zones currently occupied, it is expected to become abundant in the prairie provinces and across most of southern Canada.

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