Program     Turbulence and scaling processes in the ocean       Poster Modification of parametric subharmonic instability in the presence of background geostrophic currents P-P3-06-S Wei Yang* , Ocean University of China Toshiyuki Hibiya, The University of Tokyo Yuki Tanaka, The University of Tokyo Liang Zhao, Tianjin University of Science and Technology Hao Wei, Tianjin University Presenter Email: yangwouc@163.com The parametric subharmonic instability (PSI), a kind of triad wave resonant interaction, is capable of rapidly cascading the energy of internal tides to smaller-scale waves of half the tidal frequency. Regarding with the simulation of internal tide energy cascade through PSI, most studies studied the internal tides propagating through a quiescent ocean, hence ignoring the presence of background relative vorticity. Here, we showed for the first time that the presence of background relative vorticity can significantly modify the behavior of PSI through changing the local effective Coriolis frequency. A series of idealized experiments at 25.4°N show that the PSI efficiency increases several times above the background value where positive vorticity have shifted the effective Coriolis frequency approaching the critical frequency. Also, with the negative relative vorticity low enough, significant energy transfer associated with PSI can occur at 31°N (poleward of the critical latitude for M2) which is never expected before. The presented results provide important implications on understanding the spatial distribution of diapycnal mixing in the ocean where geostrophic currents prevail.

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