Guo Shuang-Xi, Zhou Sheng-Qi, Cen Xian-Rong, Lu Yuan-Zheng
State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences.
State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences;
J Vis Exp. 2018 Sep 5(139):58316. doi: 10.3791/58316.
Diffusive convection (DC) occurs when the vertical stratified density is controlled by two opposing scalar gradients that have distinctly different molecular diffusivities, and the larger- and smaller- diffusivity scalar gradients have negative and positive contributions for the density distribution, respectively. The DC occurs in many natural processes and engineering applications, for example, oceanography, astrophysics and metallurgy. In oceans, one of the most remarkable features of DC is that the vertical temperature and salinity profiles are staircase-like structure, composed of consecutive steps with thick homogeneous convecting layers and relatively thin and high-gradient interfaces. The DC staircases have been observed in many oceans, especially in the Arctic and Antarctic Oceans, and play an important role on the ocean circulation and climatic change. In the Arctic Ocean, there exist basin-wide and persistent DC staircases in the upper and deep oceans. The DC process has an important effect on diapycnal mixing in the upper ocean and may significantly influence the surface ice-melting. Compared to the limitations of field observations, laboratory experiment shows its unique advantage to effectively examine the dynamic and thermodynamic processes in DC, because the boundary conditions and the controlled parameters can be strictly adjusted. Here, a detailed protocol is described to simulate the evolution process of DC staircase structure, including its generation, development and disappearance, in a rectangular tank filled with stratified saline water. The experimental setup, evolution process, data analysis, and discussion of results are described in detail.
扩散对流（DC）发生在垂直分层密度由两个具有明显不同分子扩散率的相反标量梯度控制时，且扩散率较大和较小的标量梯度分别对密度分布有负向和正向贡献。扩散对流发生在许多自然过程和工程应用中，例如海洋学、天体物理学和冶金学。在海洋中，扩散对流最显著的特征之一是垂直温度和盐度剖面呈阶梯状结构，由具有厚均匀对流层和相对薄且高梯度界面的连续阶梯组成。扩散对流阶梯已在许多海洋中被观测到，特别是在北冰洋和南大洋，并且在海洋环流和气候变化中发挥着重要作用。在北冰洋，上层和深层海洋中存在全盆地范围且持续存在的扩散对流阶梯。扩散对流过程对上层海洋的斜压混合有重要影响，并且可能显著影响表层冰融化。与现场观测的局限性相比，实验室实验显示出其独特优势，能够有效检验扩散对流中的动力学和热力学过程，因为边界条件和控制参数可以严格调整。在此，描述了一个详细的实验方案，用于在装满分层盐水的矩形水箱中模拟扩散对流阶梯结构的演化过程，包括其产生、发展和消失。详细描述了实验装置、演化过程、数据分析和结果讨论。
