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Center for Nonlinear Studies |
Internal waves are believed to be of primary importance as they affect ocean mixing and energy transport. Several processes can lead to the breaking of internal waves and they usually involve non linear interactions between waves. In this work, we study experimentally the Parametric Subharmonic Instability (PSI), which provides an efficient mechanism to transfer energy from large to smaller scales. It consists in the destabilization of a primary wave and the spontaneous emission of two secondary waves, of lower frequencies and different wave vectors. Using a time-frequency analysis, we observe the time evolution of the secondary waves, thus measuring the growth rate of the instability. In addition, a Hilbert transform method allows us to measure the different wave vectors. We compare these measurements with theoretical predictions, and study the dependance of the instability with primary wave frequency and amplitude. In addition we will present a preliminary study of how internal waves can produce mixing in the stratified fluid, and how this mixing is enhanced by the presence of PSI.
Host: Robert Ecke, CNLS, 667-1444, ecke@lanl.gov