The role of buoyancy–frequency oscillations in the generation of mountain gravity waves |
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Authors: | Ivan Skopovi T R Akylas |
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Institution: | (1) Department of Mechanical Engineering, MIT, Cambridge, MA 02139, USA |
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Abstract: | There is evidence from balloon measurements that atmospheric buoyancy–frequency profiles, apart from a sharp increase (roughly
by a factor of two) at the tropopause, often feature appreciable oscillations (typical wavelength 1–2 km) with altitude. It
is argued here that such short-scale oscillatory variations of the background buoyancy frequency, which usually are ignored
in theoretical models, can have a profound effect on the generation of mountain waves owing to a resonance mechanism that
comes into play at certain wind speeds depending on the dominant oscillation wavelength. A simple linear model assuming small
sinusoidal buoyancy–frequency oscillations suggests, and numerical solutions of the Euler equations for more realistic flow
conditions confirm, that under resonant conditions the induced gravity-wave activity is significantly increased above and
upstream of the mountain, similarly to resonant flow of finite depth over topography.
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Keywords: | Stratified flow Gravity waves Mountain waves |
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