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Assessment of a gravity‐wave drag parametrization with PYREX data
Author(s) -
Beau Isabelle,
Bougeault Philippe
Publication year - 1998
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.49712454906
Subject(s) - parametrization (atmospheric modeling) , froude number , momentum (technical analysis) , gravity wave , drag , computation , physics , mechanics , orographic lift , divergence (linguistics) , flow (mathematics) , meteorology , classical mechanics , mathematics , gravitational wave , algorithm , optics , precipitation , finance , astrophysics , economics , radiative transfer , linguistics , philosophy
An original methodology is developed to assess the behaviour of gravity‐wave drag parametrizations. It relies on the computation of differences between numerical simulations at various horizontal resolutions. The terms to parametrize are extracted from comparisons between the full momentum budgets of the high‐resolution and low‐resolution simulations. The parametrization under assessment is firstly calibrated off‐line to reproduce at best the residual vertical momentum flux, then it is introduced in the numerical model for an on‐line verification simulation. The methodology is applied to the ECMWF parametrization (in its 1990 version), using four meteorological situations well documented during the PYREX field experiment. The results show that the classical formulation, limiting the effect of orographic waves to the vertical divergence of the momentum flux, is well founded. However, it is shown that the optimal coefficients of the tested scheme are in general much larger than the value recommended at the time, and quite variable from one case to another. The variability of the low‐level blocking effect with the Froude number of the incident flow is suggested as a possible explanation.