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Momentum budgets over idealized orography with a non‐hydrostatic anelastic model. II: Three‐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.49712555807
Subject(s) - vortex , orography , parametrization (atmospheric modeling) , mechanics , physics , orographic lift , drag , momentum (technical analysis) , wave drag , classical mechanics , geology , meteorology , drag coefficient , precipitation , quantum mechanics , radiative transfer , finance , economics
The study of the interaction between two‐dimensional nonlinear orographic effects and the synoptic flow presented in Part I of this paper is extended to three‐dimensional (3D) flows. Numerical simulations of idealized 3D orographic flows are carried out with a non‐hydrostatic anelastic model to test the hypothesis of current drag parametrizations through calculations of momentum budgets in different domains of variable size representative of a grid mesh of a general‐circulation model (GCM). Parametrizations are tested in three nonlinear regimes of 3D orographic flows. In the regime of quasi‐symmetrical lee vortices, the large‐scale flow is decelerated in a restricted region located below the maximum height of the obstacle. When the symmetry of the lee vortices is altered, by a long model integration or by introduction of a perturbation, the flow evolves towards the vortex‐shedding regime. A very long integration of the model numerically shows the saturation of the disturbance after 140 units of dimensionless time. Budgets of momentum indicate that vortex shedding significantly enhances the large‐scale flow deceleration, still located below the maximum height of the obstacle. For a case of non‐breaking 3D trapped lee waves, the mean flow is decelerated in the trapping region. Comparison of the predictions of two gravity‐wave drag parametrizations with the results of fine‐mesh simulations shows that the parametrization of 3D subgrid‐scale orographic effects in a GCM takes into account most of the physical phenomena existing in the set of idealized flows.