The Wind Climate in a Mountain Valley in Northern Sweden

The wind climate in a valley has been studied. Long time data from towers along the valley have been used, together with data from two field campaigns. The campaigns took place during two weeks in May 1999 and two weeks in September 2000. During the field campaigns wind speed and direction were measured, both with small masts and with pilot balloon tracking. A comparison of single and double theodolite tracking is performed. It is found that single theodolite tracking is good enough to use. The ascent rate of the balloon is seen to be slightly higher than the earlier assumed 4 m/s. An investigation of the wind field along and across the valley have been done. The result show that high mean wind speed are found at the sites were the valley is rather narrow. The wind direction was then either upstream or downstream the valley. The mean wind speed at Suorva is 6.6 m/s. Channelling effects, forced- and pressure-driven channelling, seem to dominate the winds in the valley giving high speeds. No correlation is found between the magnitude of the geostrophic wind and the wind in the valley. High winds in the valley is obtained both with high and low geostrophic winds. A peak in the southwesterly direction for the distribution of geostrophic wind is seen. This is due to the common synoptic situation with a low pressure area outside the coast of Norway. Data from sites across the valley show that the highest wind speeds are found at the northeastern side and the lowest at the southwestern side. The stratification is found to have strong effect of the air flow around a hill and the local terrain. When the stratification was stable the air was blowing around Jiertasuoloj, an island of about 50 m height. When the air is unstable the air is instead blowing over Jiertasuoloj