Spatial and temporal distribution of the wind‐induced internal wave energy available for deep water mixing in the North Pacific

Abstract

Using a three‐dimensional multilevel numerical model, we examine the distribution of the wind‐induced near‐inertial internal wave energy in the North Pacific. Energetic low vertical mode near‐inertial internal waves are excited at 30°–45°N in the western and central North Pacific by traveling midlatitude storms during winter and at 10°–30°N in the western North Pacific by tropical cyclones during fall. Thus excited internal waves propagate equatorward down to 5°–15°N, where their frequencies are twice the local inertial frequencies. Parametric subharmonic instability can then transfer their energy across the local internal wave vertical wavenumber spectrum to small dissipation scales. The calculated results show that low vertical mode double‐inertial frequency internal waves are very weak at the times and locations of previous microstructure measurements, which suggests that the observed value of diapycnal diffusivity of ∼10−5 m2 s−1, an order of magnitude lower than required to satisfy the large‐scale advective‐diffusive balance of the thermohaline circulation, may not be representative.