The wind climate in an arctic mountain valley

The wind climate in a mountain valley in the northernmost part of Sweden (18°E, 67°N) have been examined. The terrain in this area consists of 1200 to 2000 m high mountains on both sides of a valley with its axis in a direction from northwest to southeast. The water surfaces of the lakes and dams at the valley bottom are around 430 m above sea level. Observations made at four sites along the valley have been used.

Results from continuous measurements, indicate that high mean wind speed climates may be found also in low elevation terrain of the Scandinavian mountain range. The annual mean wind speed (at 10 m) was estimated to be 6.6 m/s at Suorva, a site situated at the valley bottom where it is rather narrow (2-3 km). The highest observed 1 min average wind speed was 32 m/s at 35 m height. Strong evidence of channelling was found in the wind direction distribution at Suorva, which showed two distinct peaks in the direction of the valley. The same dominant peaks in the wind direction was not found at Ritsem, located on the northern side of a wider section of the valley, which also show a much lower mean wind speed, 3.0 m/s. A simulated wind climatology, performed with a three-dimensionell, hydrostatic mesoscale model with a higher order turbulence closure - the MIUU model, also shows large wind climate differences along and across this valley, in agreement with these measurements.

An important contribution to increase the knowledge of the wind field in this valley are the additional measurements performed during 5-16 May 1999, with three small masts (of about 3 m height) located across the valley at one of the sites (Suorva), together with radio soundings (three times a day) and pilot balloon measurements (at three sites simultaneously, across or along the valley, during several days). A large variability is often seen in these measurements, both in time and in space. In the measurements across the valley at Suorva, the strongest winds were often found at the eastern side of the valley. At one site the wind speed could vary 4-5 m/s over a few hours time period, while at the same time constantly high winds were observed at another site. A low level jet was quite often seen in the measurements. Several times the wind speed maximum was at a very low height, below the highest measurement level in the main tower at Suorva (i.e. below 36 m). Gravity waves, caused by the stable stratification and the topography, are seen in the wind measurements during some days. These waves were also seen in cloud formations.