Internal Wave Induced Sub-inertial Currents (IWISC)

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The flow of energy from the winds and tides through the ocean's internal gravity wave field may have far-reaching consequences, impacting even the qualitative nature of the abyssal ocean's circulation, with attendant implications for global climate fluctuations. Consequently, understanding the pathways of this energy flow is more than just an esoteric exercise in geophysical fluid dynamics. Until now, there has been little evidence for the proposition that an important pathway for energy leaving the internal wave band in the open ocean might be by the direct generation of non-resonant, non-propogating, sub-inertial motions.In this study, a researcher at the University of Hawaii will further explore the observational evidence for such a process acting on inertial and semi-diurnal internal waves. For simplicity, the process is referred to as "Internal Wave Induced Sub-inertial Currents" or IWISC. He proposes that a non-linear interaction between the semi-diurnal internal tide (nominally at the M2 frequency) and the inertial oscillations (at frequency f) results in the generation of these sub-inertial motions which exist around the frequency of M2 minus f. Preliminary analytical modeling and numerical simulations with a primitive equation model support this conjecture, but more work is needed to define the dynamics of its generics. Most importantly, this observation of the M2-f interaction may presage the existence of a whole class of interactions that pump energy out of the internal wave field and into sub-inertial motions in the open ocean. To explore this IWISC phenomenon analysis of historical datasets, simulations with a primitive equation numerical model, and theoretical analysis will be used. The results from this work significantly impact the estimates of the mount of internal wave energy that is available for mixing the abyssal ocean. In addition to the intellectual merit of the work, this research will support a graduate student as he conducts much of the proposed work under the close supervision of his advisor.