Complex air flows in the lower tamar valley, Tasmania: Some observations

Abstract

As part of an air quality study undertaken in the lower Tamar Valley in northern Tasmania where Bell Bay industrial area is located, the vertical structures of temperature and wind were investigated within the lowest km of the atmosphere by tethered balloon soundings at a location about 1 km SE of an aluminium smelter. A total of nine measurements was made on 23 September and 5–6 October 1982. The overnight stable air layers (including the isothermal layer) were able to develop up to a height of 200–300 m above the ground. An elevated inversion at a height of 425–530 m was also observed during the evening of 5 October 1982. The wind field was influenced by the local drainage flows (notably the NE, SW katabatic winds and the SE down-valley flows) in the morning at the lower level, and synoptic scale winds above 200 m. Interaction of the persistent NE winds with the ridges bounding the lower Tamar Valley led to the formation of a stagnant layer up to a height of 80 m in the area during the middle of the night of 5–6 October (the Froude number of 1.39 was consistent with this), and facilitated the formation of katabatic winds on the slopes of the Asbestos/Dazzler Ranges, leading to a SW drainage flow along the general direction of West Arm, spreading out across the river, and occasionally reaching the Bell Bay industrial area as a W-WNW flow. Analysis of the 10−m wind further shows that the complexity of the topography of the coastal valley greatly affects both the local and regional winds, which may have profound implications for air pollution in the area.