Pressure-Driven Channeling Effects in Bent Valleys

Abstract

Previous investigations of dynamic channeling of airflow in mountain valleys have been limited to straight valleys, where a constant along-valley component of the synoptic pressure gradient can be assumed. In nature, however, valleys are often curved or bent, that is, composed of segments of different orientations. In these valleys, the along-valley component of the synoptic-scale pressure gradient differs from one segment of the valley to another. This paper presents a simple conceptual model of the changes in wind speed and direction that will occur along the axis of a bent valley because of pressure-driven channeling when adjacent valley segments have a different orientation but constant width and depth. Special emphasis is given to horizontal flow convergence or divergence and compensatory lifting or subsidence within (and above) the valley. The processes are discussed for situations in which differently oriented but straight adjacent valley segments form a bent valley; however, the results can easily be adapted to smoothly curving valleys. The effects of the magnitude of the angle between segments (or, alternately, valley curvature) on the expected flow patterns in the valley are analyzed. The conceptual model derived for flow patterns in curved or bent valleys has a wide range of applications in mountainous terrain, including the dispersion of air pollutants, cloud formation and dissolution, precipitation, bushfire propagation, wind energy potential, and aviation.