Upstream Effects of Mesoscale Mountains

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Abstract
The Alpine Experiment (ALPEX) has revealed that low-level air is typically diverted around the Alps without reaching the mountaintop. In pursuit of an understanding of the physical basis of this phenomenon and of its generality, we have explored the characteristics of orographic blocking of a rotating continuously stratified quid, as revealed in a simple model problem retaining full nonlinear and transient effects. Hydrostatic dynamics is assumed, and the obstacle is taken to be an infinitely long ridge with height h(x). The key questions treated are the strength of the upstream deceleration of cross-mountain flow and the length scale over which the decelerated region extends. By means of scale analysis, the controlling parameters are found to be the Rossby number Ro = U/fL and the Froude number Fr = Nhm/U, where U is the speed of the oncoming flow, f is the Coriolis parameter, L the mountain half-width, N the Brunt-Väisälä frequency, and hm is the maximum mountain height. The scale analysis also... Abstract The Alpine Experiment (ALPEX) has revealed that low-level air is typically diverted around the Alps without reaching the mountaintop. In pursuit of an understanding of the physical basis of this phenomenon and of its generality, we have explored the characteristics of orographic blocking of a rotating continuously stratified quid, as revealed in a simple model problem retaining full nonlinear and transient effects. Hydrostatic dynamics is assumed, and the obstacle is taken to be an infinitely long ridge with height h(x). The key questions treated are the strength of the upstream deceleration of cross-mountain flow and the length scale over which the decelerated region extends. By means of scale analysis, the controlling parameters are found to be the Rossby number Ro = U/fL and the Froude number Fr = Nhm/U, where U is the speed of the oncoming flow, f is the Coriolis parameter, L the mountain half-width, N the Brunt-Väisälä frequency, and hm is the maximum mountain height. The scale analysis also...

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