[AOS11-P06] Decay rates of internal tides estimated by an improved wave-wave interaction analysis
Keywords:Internal tides, wave dynamics, parametric subharmonic instability
In this study, by reformulating the kinetic equation for long internal waves and developing its calculation method, we estimate the energy decay rates of the low-vertical-mode semi-diurnal internal tides interacting with the "ubiquitous" oceanic internal wave field. The result shows rapid energy decay of the internal tides, typically within O(10) days for the lowest-mode component, near their critical latitudes. Energy lost from the internal tides is then transferred to high-mode near-inertial components in the upper ocean. The decay time of internal tides obtained here is several-fold shorter than those in the classical studies and, additionally, varies by a factor of two depending on the local depth and density structure.
We suggest from this study that the numerical integration of the kinetic equation is a more effective approach than recognized to determine the decay parameter of wave energy, which is indispensable for the global ocean models.