Quantification of the intensity of mixing hotspots to clarify the dynamics of the global meridional overturning circulation

利用无绳系自由落体微结构剖面仪“TurboMAP-D”采集了太平洋内部共53条速度微结构剖面。我们发现，在20°-30°N附近，赤道扩散系数与半日内潮局部有效能量密度的对数大致成正比，并在伊豆-小川海脊附近达到10^&lt；-4。相反，日向扩散系数保持在极地30°N和赤道20°N的~10^&lt；-5&gt；m^2s；-1量级，与局部可用半日内潮汐能量大小无关。我们已经证实，这些观察到的特征与Hibiya等人预测的主温跃层中昼夜扩散率的全球地图是一致的。(2006)。使用一个理想化的海洋环流模式，我们接下来检验了Hibiya等人预测的“混合热点”的影响。(2006)，关于太平洋经向翻转环流。我们发现，混合热区估计的上升流不足以平衡深水生产。此外，横跨赤道的深水向北输送的量比以前的海流计系泊和水文调查估计的要少得多。对这些结果的一个可信的解释是，从观测结果来看，太平洋经向翻转环流的规模被高估了。我们对以前的海洋环流模式的有效性提出了质疑，在这些模式中，日平均扩散系数被特别分配，以获得从海流计系泊和水文测量中建议的海流等级。

The un-tethered free-fall microstructure profiler “TurboMAP-D" was used to collect a total of 53 velocity microstructure profiles in the interior of the Pacific Ocean. We found the diapycnal diffusivity at 20°-30°N was roughly in proportional to the logarithm of the locally available energy density of the semidiurnal internal tide and reached more than 10^<-4> m^2s^<-1> near the Izu-Ogasawara Ridge. In contrast, diapycnal diffusivity was found to remain of the order of〜10^<-5> m^2s^<-1> poleward of 30°N and equatorward of 20°N, irrespective of the amount of locally available semidiurnal internal tide energy. We have confirmed that these observed features are consistent with the global map of diapycnal diffusivity in the main thermocline predicted by Hibiya et al. (2006).Using an idealized ocean general circulation model, we next examined the effect of“mixing hotspots", predicted by Hibiya et al. (2006), on the meridional overturning circulation of the Pacific Ocean. We have found that the estimated upwelling in the mixing hotspots is not sufficient to balance deep-water production. In addition, the northward transport of the deep water crossing the equator was found to be much less than estimated from previous current meter moorings and hydrographic surveys. One plausible explanation for these results is that the magnitude of the meridional overturning circulation of the Pacific Ocean has been overestimated from observations. We raise doubts about the validity of previous ocean general circulation models where diapycnal diffusivity is assigned ad hoc to attain the current magnitude suggested from current meter moorings and hydrographic surveys.