Wind data for 2001-05 indicate that a minimum annual mean wind speed of 6 [ms.sup.-1] begins at about 150 m above the Whitehorse valley floor, or 850 m above sea level.
The most relevant criterion for new wind energy sites is that annual mean wind speed should exceed a threshold of 6 [ms.sup.-1] (21.6 km/hr).
The 2001-05 annual mean wind speed above the Whitehorse station was 6.9 at 900 m ASL, 7.3 at 1200 m, 7.1 at 1500 m, and 7.3 [ms.sup.-1] at 1800 m.
The positive trend in annual mean wind speed over 50 years suggests that wind farm economics are in the long run becoming more attractive.
Figure 10 shows isotachs of annual mean wind speed overlying elevation profiles from cross-sections drawn across the Whitehorse Valley in Figure 6.
* At what elevations will threshold annual mean wind speeds for cost-efficient wind-energy production be attained?