Wind Climate of the Whitehorse Area

Abstract

Measurements from Whitehorse upper-air and nearby mountaintop stations were analyzed with a focus on wind energy development in the region. Fifty years of measurements indicate the region has become warmer and windier. Measurements at the upper-air station have shown increases of 2.7°C for surface temperature and 1 m s-1 for mid-valley winds over the past 50 years (1956– 2005). The winters have warmed more dramatically than the summers. Winter temperature inversions have become shallower, and a mid-valley winter jet has become a predominant feature. Wind data for 2001–05 indicate that a minimum annual mean wind speed of 6 m s-1 begins at about 150 m above the Whitehorse valley floor, or 850 m above sea level. At this elevation and higher, wind speeds reach a maximum in December and a minimum in July. The predominant wind direction above the mountaintops was from the southwest, while stations within the Whitehorse Valley recorded winds from the south-southeast. Stations that were more exposed to the southwest reported more predominant winds from this direction. An analysis of the relationship between geostrophic and valley winds concluded that, relative to winds aloft, valley winds were as strong in parallel valleys as they were in perpendicular valleys. The pressure gradients associated with the winds aloft were the dominant forcing mechanism for winds in a perpendicular valley. Geostrophic winds that were parallel to the valley forced the valley winds along the same direction through a downward momentum transport. Wintertime inversions suppress the downward momentum transport, but pressure-driven winds are only indirectly modulated by stratification (because of turbulent friction, which is likely to be suppressed by stable stratification) and so are less sensitive to that factor. Further investigation of wind energy potential is recommended for hills within the valleys, particularly in areas well exposed to southwest winds.