Gravity-wave drag parametrization over complex terrain: The effect of critical-level absorption in directional wind-shear
✍ Scribed by Glenn Shutts
- Publisher
- John Wiley and Sons
- Year
- 1995
- Tongue
- English
- Weight
- 916 KB
- Volume
- 121
- Category
- Article
- ISSN
- 0035-9009
No coin nor oath required. For personal study only.
✦ Synopsis
Abstract
Most schemes to parametrize gravity‐wave drag effectively assume that the total wave‐stress is associated with a single wave‐vector pointing in the direction of the stress vector. However, the wave stress over real terrain is an integral over all azimuthal directions of wave‐vector contributions. In unidirectional flow, all of these modes will have a critical line at the same height—if one exists. However, if the wind turns montonically with height, by whatever degree, critical‐level absorption will occur at all heights for some portion of the wave spectrum. the resultant critical‐line wave‐drag is always normal to the local wind direction and the wave stress itself turns with height. This contrasts with the height‐independent stress assumption used in parametrizing gravity‐wave drag outside regions where the wave stress is saturated.
A practical approach to computing the gravity‐wave stress over anisotropic orography, which includes this selective critical‐level absorption effect, will be presented. This will be supported by an analytical model calculation for constant‐shear flow with wind turning.