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Momentum budgets over idealized orography with a non‐hydrostatic anelastic model. I: Two‐dimensional flows
Author(s) -
Héreil Philippe,
Stein Joël
Publication year - 1999
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49712555806
Subject(s) - orography , orographic lift , stratosphere , breaking wave , drag , mechanics , momentum (technical analysis) , flow (mathematics) , hydrostatic equilibrium , mean flow , physics , wave drag , troposphere , geology , meteorology , wave propagation , drag coefficient , precipitation , turbulence , finance , quantum mechanics , economics
Numerical simulations of two‐dimensional (2D) mountain waves are carried out with a non‐hydrostatic anelastic model to investigate the interaction between 2D nonlinear orographic effects and the synoptic flow. the problem is idealized to isolate the essential features of real orographic flows. For each simulation, the complete momentum equations of the model are summed in different domains of variable size representative of a grid mesh of a general‐circulation model. the resulting budgets of momentum, instantaneous or averaged in time, are used to test the hypothesis of current drag parametrizations in three nonlinear regimes of 2D orographic flows. For mountain waves breaking in the troposphere, the mean flow is decelerated in the vertical between the ground and the theoretical breaking level. In the horizontal, the deceleration of the large‐scale flow is uniformly distributed by non‐resolved acoustic waves. When non‐Boussinesq effects lead mountain waves to break in the lower stratosphere, the large‐scale flow is decelerated on a vertical wavelength centred on the breaking level. In the case of non‐breaking trapped lee waves, the deceleration of the mean flow is strongly dependent of the non‐hydrostatic character of the primary propagating wave. Off‐line tests of two drag parametrizations show that some adaptations are necessary to improve the prediction of the impact of subgrid‐scale orographic effects on the large‐scale flow for the set of investigated idealized orographic events.