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

使用无系留自由落体微结构剖面仪“TurboMAP-D”在太平洋内部收集了总共53个速度微结构剖面。结果表明，在20° ~ 30 ° N范围内，经向扩散率与半日内潮局部有效能量密度的对数成正比，在<-4><-1>伊豆-小笠原海岭附近达10 μ m^2s^以上。相反，<-5><-1>无论当地可利用的半日内潮能量的多少，向30°N极地方向和向20°N赤道方向的经向扩散率都保持在100 ^ m^2s^的数量级。我们证实了这些观测特征与Hibiya等人（2006）预测的全球主温跃层底辟扩散率图相一致。接下来，我们使用理想化的海洋环流模式，检验了Hibiya等人（2006）预测的“混合热点”对太平洋纬向翻转环流的影响。我们已经发现，估计在混合热点的上升流是不足以平衡深水生产。此外，向北运输的深水穿越赤道被认为是远远低于估计从以前的流速计停泊和水文调查。对这些结果的一个合理解释是，太平洋纬向翻转环流的大小被观测高估了。我们提出了怀疑以前的海洋环流模型的有效性，其中的diapycnal扩散系数分配特设的电流表停泊和水文调查，以达到目前的幅度建议。

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.