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Abstract
The gravity waves (GWs) generated by potential vorticity (PV) anomalies in a rotating stratified shear flow are examined under the assumptions of constant vertical shear, twodimensionality, and unbounded domain. Near a PV anomaly, the associated perturbation is well modeled by quasigeostrophic theory. This is not the case at large vertical distances, however, and in particular beyond the two inertial layers that appear above and below the anomaly; there, the perturbation consists of vertically propagating gravity waves. This structure is described analytically, using an expansion in the continuous spectrum of the singular modes that results from the presence of critical levels.
Several explicit results are obtained. These include the form of the EliassenPalm (EP) flux as a function of the Richardson number N2/Lambda(2), where N is the BruntVaisala frequency and Lambda the vertical shear. Its nondimensional value is shown to be approximately exp(pi N/Lambda)/8 in the farfield GW region, approximately twice that between the two inertial layers. These results, which imply substantial waveflow interactions in the inertial layers, are valid for Richardson numbers larger than 1 and for a large range of PV distributions. In dimensional form they provide simple relationships between the EP fluxes and the largescale flow characteristics.
As an illustration, the authors consider a PV disturbance with an amplitude of 1 PVU and a depth of 1 km, and estimate that the associated EP flux ranges between 0.1 and 100 mPa for a Richardson number between 1 and 10. These values of the flux are comparable with those observed in the lower stratosphere, which suggests that the mechanism identified in this paper provides a substantial gravity wave source, one that could be parameterized in GCMs.
Original language  English 

Pages (fromto)  157170 
Number of pages  14 
Journal  Journal of the Atmospheric Sciences 
Volume  67 
Issue number  1 
DOIs  
Publication status  Published  Jan 2010 
Keywords
 Gravity waves
 Shear structure/flows
 Potential vorticity
 Stratosphere
 Waves
 atmospheric
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 1 Finished

Generation of unbalanced motion at horizontal boundaries in the atmosphere and the oceans
1/10/08 → 30/07/11
Project: Research