Mountain waves in two-layer sheared flows: Critical-level effects, wave reflection, and drag enhancement

• Type: Article in International Scientific Journal
• Date: 2008

Authors

Teixeira, MAC (Author) Other; Miranda, PMA (Author) Other; Argain, JL (Author) Other

Journal

The Journal is awaiting validation by the Administrative Services.

Title: JOURNAL OF THE ATMOSPHERIC SCIENCES

Vol. 65

Pages: 1912-1926

ISSN: 0022-4928

Indexing

ISI Web of Knowledge - 21 Citations

Scopus - 21 Citations

Other information

Authenticus ID: P-003-Z3G

DOI: 10.1175/2007jas2577.1

Abstract (EN): Internal gravity waves generated in two-layer stratified shear flows over mountains are investigated here using linear theory and numerical simulations. The impact on the gravity wave drag of wind profiles with constant unidirectional or directional shear up to a certain height and zero shear above, with and without critical levels, is evaluated. This kind of wind profile, which is more realistic than the constant shear extending indefinitely assumed in many analytical studies, leads to important modifications in the drag behavior due to wave reflection at the shear discontinuity and wave filtering by critical levels. In inviscid, nonrotating, and hydrostatic conditions, linear theory predicts that the drag behaves asymmetrically for backward and forward shear flows. These differences primarily depend on the fraction of wavenumbers that pass through their critical level before they are reflected by the shear discontinuity. If this fraction is large, the drag variation is not too different from that predicted for an unbounded shear layer, while if it is small the differences are marked, with the drag being enhanced by a considerable factor at low Richardson numbers (Ri). The drag may be further enhanced by nonlinear processes, but its qualitative variation for relatively low Ri is essentially unchanged. However, nonlinear processes seem to interact constructively with shear, so that the drag for a noninfinite but relatively high Ri is considerably larger than the drag without any shear at all.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 15