Original scientific paper
A LINEAR STUDY OF HIGH-DRAG STATES AND FLOW STAGNATION PRODUCED BY MOUNTAIN WAVES
Miguel A.C. Teixeira
orcid.org/0000-0003-1205-3233
; Geophysics Centre and Department of Physics, University of Lisbon Edifício C8, Campo Grande, 1749-016 Lisbon, Portugal
Pedro M.A. Miranda
; Geophysics Centre and Department of Physics, University of Lisbon Edifício C8, Campo Grande, 1749-016 Lisbon, Portugal
José L Argain
; Department of Physics, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
Maria Antónia Valente
; Geophysics Centre and Department of Physics, University of Lisbon Edifício C8, Campo Grande, 1749-016 Lisbon, Portugal
Abstract
A linear model of gravity waves generated by stratified airflow over mountains is developed. The model provides simple, closed-form formulas for the surface drag in a situation where conditions for wave resonance exist. The wind is constant near the surface and decreases linearly above. The drag normalized by its value in the absence of shear is found to depend on two parameters: the height of the interface where the shear is discontinuous and the
Richardson number, Ri, in the region above. This drag attains maxima when the height of the interface induces constructive interference between the upward and downward propagating reflected waves, and minima when there is destructive interference. The amplitude of the drag modulation becomes larger for lower Ri. It is also shown that, for Ri<2.25, the locations where wave breaking is first predicted to occur in flow over a 2D ridge become displaced
horizontally and vertically by an amount depending on Ri.
Keywords
Mountain waves; High-drag states; Resonance
Hrčak ID:
64670
URI
Publication date:
15.12.2005.
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