Resonant gravity-wave drag enhancement in linear stratified flow over mountains

Teixeira, M. A. C. ORCID: https://orcid.org/0000-0003-1205-3233, Miranda, P. M. A., Argain, J. L. and Valente, M. A. (2005) Resonant gravity-wave drag enhancement in linear stratified flow over mountains. Quarterly Journal of the Royal Meteorological Society, 131 (609). pp. 1795-1814. ISSN 1477-870X doi: 10.1256/qj.04.154

Abstract/Summary

High-drag states produced in stratified flow over a 2D ridge and an axisymmetric mountain are investigated using a linear, hydrostatic, analytical model. A wind profile is assumed where the background velocity is constant up to a height z1 and then decreases linearly, and the internal gravity-wave solutions are calculated exactly. In flow over a 2D ridge, the normalized surface drag is given by a closed-form analytical expression, while in flow over an axisymmetric mountain it is given by an expression involving a simple 1D integral. The drag is found to depend on two dimensionless parameters: a dimensionless height formed with z_1, and the Richardson number, Ri, in the shear layer. The drag oscillates as z_1 increases, with a period of half the hydrostatic vertical wavelength of the gravity waves. The amplitude of this modulation increases as Ri decreases. This behaviour is due to wave reflection at z_1. Drag maxima correspond to constructive interference of the upward- and downward-propagating waves in the region z < z_1, while drag minima correspond to destructive interference. The reflection coefficient at the interface z = z_1 increases as Ri decreases. The critical level, z_c, plays no role in the drag amplification. A preliminary numerical treatment of nonlinear effects is presented, where z_c appears to become more relevant, and flow over a 2D ridge qualitatively changes its character. But these effects, and their connection with linear theory, still need to be better understood.

Item Type	Article
URI	https://reading-clone.eprints-hosting.org/id/eprint/29251
Identification Number/DOI	10.1256/qj.04.154
Refereed	Yes
Divisions	Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology No Reading authors. Back catalogue items
Publisher	Royal Meteorological Society
Download/View statistics	View download statistics for this item