The effect of upstream wind direction on atmospheric flow in the vicinity of a large mountain

Abstract

A series of idealized simulations is conducted to investigate how the upstream wind direction impacts on the flow in the vicinity of a large elliptical mountain, oriented north–south. The upstream wind speed and stability are kept constant, there is no surface friction, the Rossby number is low and the non-dimensional mountain height, ĥ = 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 ĥ, the flow is blocked for low aspect ratio while it is not blocked for high aspect ratio. Furthermore, the upstream barrier wind is more pronounced when the upstream flow is from the south-west than from the north-west. Both these features are linked to the interaction of the Coriolis force with the mountain-induced flow anomalies. The drag force and the pressure deficit in the wake are greater in the south-west cases than in the north-west cases. These features are linked, as the main contribution to the drag being greater in the south-west cases is a negative pressure anomaly over the lee slope. The difference downstream of the mountain is linked to the interaction of the low-level flow anomalies and the Coriolis force. Copyright © 2005 Royal Meteorological Society