4.2 Local winds, drag and wakes in idealized orographic flow at low Rossby number

Monday, 21 June 2004: 3:45 PM
G. N. Petersen, Univ. of Oslo, Oslo, Norway and Univ. of Iceland, Oslo, Iceland; and H. Ólafsson and J. E. Kristjánsson

A series of idealized simulations is conducted to investigate how the upstream wind direction impacts the flow in the vicinity of a large mountain. The upstream wind speed and stability are kept constant, there is no surface friction, the Rossby number is low and the nondimensional mountain height, Nh/U is varied from 1 to 4.5. The flow pattern varies greatly with wind direction and a number of features of orographic flows where the Coriolis force is important are found. For a given Nh/U the flow is blocked for low aspect ratio while it is not blocked for high aspect ratio. The upstream barrier wind, the drag force and the wake are more prounounced when the impinging winds are from the southwest, than if they are from the northwest. These features are linked and they can be explained by the interaction of the Coriolis force with the mountain and the low level flow anomalies. Application to real flow on the earth are discussed.

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