Teixeira, M. A. C.Argaín, José Luís AlmaguerMiranda, P. M. A.2018-12-072018-12-072013-040035-9009http://hdl.handle.net/10400.1/11097The surface drag force produced by trapped lee waves and upward propagating waves in non-hydrostatic stratified flow over a mountain ridge is explicitly calculated using linear theory for a two-layer atmosphere with piecewise-constant static stability and wind speed profiles. The behaviour of the drag normalized by its hydrostatic single-layer reference value is investigated as a function of the ratio of the Scorer parameters in the two layers l2/l1 and of the corresponding dimensionless interface height l1H, for selected values of the dimensionless ridge width l1a and ratio of wind speeds in the two layers. When l2/l1 1, the propagating wave drag approaches 1 in approximately hydrostatic conditions, and the trapped lee wave drag vanishes. As l2/l1 decreases, the propagating wave drag progressively displays an oscillatory behaviour with l1H, with maxima of increasing magnitude due to constructive interference of reflected waves in the lower layer. The trapped lee wave drag shows localized maxima associated with each resonant trapped lee wave mode, occurring for small l2/l1 and slightly higher values of l1H than the propagating wave drag maxima. As l1a decreases, i.e. the flow becomes more non-hydrostatic, the propagating wave drag decreases and the regions of non-zero trapped lee wave drag extend to higher l2/l1. These results are confirmed by numerical simulations for l2/l1 = 0.2. In parameter ranges of meteorological relevance, the trapped lee wave drag may have a magnitude comparable to that of propagating wave drag, and be larger than the reference single-layer drag. This may have implications for drag parametrization in global climate and weather-prediction models. Copyright (c) 2012 Royal Meteorological SocietyengHydrostatic flowSurface pressureBoundary-LayerGravity-wavesSheared flowsEnhancementCurvatureResonanceProfilesFrictionjournal article10.1002/qj.2008