spatial distribution of diapycnal mixing rates in the deep waters of the North Pacific

驱动海洋内部混合的机械能被认为最初是在大尺度上提供的，然后通过深海内波谱向下传递到小的耗散尺度。在最近的数值实验中（Hibiya等人，1996，1998，2002），这种能量级联过程被证明是占主导地位的参数亚谐波不稳定性，转移能量从低垂直波数，双惯性频率波段的高垂直波数，近惯性频率波段。由此产生的增强，高垂直波数，近惯性流剪切被证明在控制湍流混合过程中起着关键作用。为了检验数值预测的能量级联过程是否在真实的深海中实际上占主导地位，我们在北太平洋的一个大区域部署了总共106个一次性海流剖面仪，以检查高垂直波数的空间分布（垂直波长<$25 m 关于我们 ）剪切。在中纬度地区，25米的垂直切变显着增强被发现在突出的半日内潮，如夏威夷海脊和伊豆小笠原海脊的半日潮汐频率超过当地惯性频率的两倍代地区。在高纬度地区，相反，没有显着的增强25米垂直切变被发现发生在另一个突出的半日internaUtides，阿留申海脊，半日潮频率小于当地惯性频率的两倍。我们发现观测到的25 m垂直切变强度的空间分布与Nagasawa等人[2000]和Niwa and Hibiya [2001]数值预测的低垂直波数、双惯性频率内波能量的空间分布有很好的相关性。这是第一个现场的证据，参数次谐波不稳定的深海内波能量转移到小的耗散尺度的主导作用。这项研究提供了一个理论框架，为未来的尝试，以确定大规模的混合结构在世界海洋。少

The mechanical energy which drives the interior mixing in the oceans is believed to be originally supplied at large scales and then transferred across the deep ocean internal wave spectrum down to small dissipation scales. In recent numerical experiments (Hibiya et al., 1996, 1998, 2002), this energy cascade process was shown to be dominated by parametric subharmonic instabilities which transfer energy from the low vertical wavenumber, double-inertial frequency wave band to a high vertical wavenumber, near-inertial frequency wave band. The resulting enhanced, high vertical wavenumber, nearinertial current shear was shown to play a key role in controlling turbulent mixing processes.In this study, to test whether or not the numerically predicted energy cascade process is actually dominant in the real deep we deployed a total of 106 expendable current profilers over a large area in the North Pacific to examine the spatial distribution of high vertical wavenumber (vertical wavelength 〜25 m … More ) shear. At mid latitudes, significant enhancement of the 25-m vertical shear was found over prominent generation regions of semidiurnal internal tides such as the Hawaiian Ridge and the Izu-Ogasawara Ridge where the semidiurnal tidal frequency exceeds twice the local inertial frequency. At high latitudes, in contrast, no significant enhancement of the 25-m vertical shear was found to occur even over another prominent generation region of semidiurnal internaUtides, the Aleutian Ridge, where the semidiurnal tidal frequency is less than twice the local inertial frequency. We find that the observed spatial distribution of the intensity of the 25-m vertical shear correlates very well with that of the low vertical wavenumber, double-inertial frequency internal wave energy numerically predicted by Nagasawa et al. [2000] and Niwa and Hibiya [2001]. This is the first in-situ evidence for the dominant role of parametric subharmonic instability in transferring deep ocean internal wave energy down to small dissipation scales. This study provides a theoretical framework for future attempts to determine the large-scale structure of mixing over the world's oceans. Less