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The generation of inertia-gravity waves in the atmosphere and oceans is examined using a geometric-optics approach. This approach considers the dynamics of a small-scale wavepacket in prescribed time-dependent, balanced flows. The wavepacket is assumed to be in the so-called wave-capture regime, where the wave intrinsic frequency is negligible compared to the Doppler shift. The dynamics is reduced to a number of ordinary differential equations describing the evolution of the wavepacket position, of its wavevector, and of three scalar fields describing the wavepacket amplitude and polarisation. The approach clearly identifies two classes of wave-generation processes: unbalanced instabilities, associated with linear interactions between inertia-gravity waves, and spontaneous generation, associated with a conversion between vortical and inertia-gravity modes. Applications to simple steady flows and to random-strain models are discussed.
|Title of host publication||IUTAM SYMPOSIUM ON TURBULENCE IN THE ATMOSPHERE AND OCEANS|
|Place of Publication||NEW YORK|
|Number of pages||10|
|Publication status||Published - 2010|
- ELLIPTIC INSTABILITY
- ROSSBY NUMBER