Gregg Michael C, Sanford Thomas B, Winkel David P
Applied Physics Laboratory, College of Fishery and Ocean Sciences, University of Washington, Seattle, Washington 98105, USA.
Nature. 2003 Apr 3;422(6931):513-5. doi: 10.1038/nature01507.
In the oceans, heat, salt and nutrients are redistributed much more easily within water masses of uniform density than across surfaces separating waters of different densities. But the magnitude and distribution of mixing across density surfaces are also important for the Earth's climate as well as the concentrations of organisms. Most of this mixing occurs where internal waves break, overturning the density stratification of the ocean and creating patches of turbulence. Predictions of the rate at which internal waves dissipate were confirmed earlier at mid-latitudes. Here we present observations of temperature and velocity fluctuations in the Pacific and Atlantic oceans between 42 degrees N and 2 degrees S to extend that result to equatorial regions. We find a strong latitude dependence of dissipation in accordance with the predictions. In our observations, dissipation rates and accompanying mixing across density surfaces near the Equator are less than 10% of those at mid-latitudes for a similar background of internal waves. Reduced mixing close to the Equator will have to be taken into account in numerical simulations of ocean dynamics--for example, in climate change experiments.
在海洋中，热量、盐分和营养物质在密度均匀的水体中比在分隔不同密度水体的界面上更容易重新分布。但是，跨密度界面的混合强度和分布对地球气候以及生物浓度也很重要。这种混合大多发生在内波破碎的地方，内波破碎会颠覆海洋的密度分层并产生湍流斑块。此前，中纬度地区内波消散速率的预测已得到证实。在此，我们展示了在北纬42度至南纬2度之间的太平洋和大西洋中对温度和速度波动的观测结果，以便将该结果扩展到赤道地区。我们发现，根据预测，消散存在很强的纬度依赖性。在我们的观测中，在类似内波背景下，赤道附近的消散率以及跨密度界面的伴随混合不到中纬度地区的10%。在海洋动力学数值模拟中，例如在气候变化实验中，必须考虑赤道附近混合减少的情况。
