南海上混合层湍流结构本征分布研究

The oceanic surface mixed layer (OSML) is the only tunnel for exchanging the momentum, heat and mass between the atmosphere and the ocean, while turbulent mixing is the dominate process in the energy and mass transport in the ocean. Most available OSML turbulent mixing parameterization models were developed in terms of numerical simulation and laboratory experiments, and they are less supported and testified with the ocean in-situ observations. In the project, we would make use of a new ocean surface platform attached with a high-resolution thermistor chain, which could be controlled and operated in any oceanic weather conditions. With this equipment and the traditional ocean mixing, hydrological and meteorological instruments, we take a long time OSML turbulent mixing measurements at the center and north regions of the South China Sea. The measured high precise temperature signals are analyzed to obtain the turbulent dissipation rate by fitting with the theoretical spectrum with the maximum likehood method. We would study the spatial distribution and temporal evolution of the OSML turbulent structures; explore the energy sources and the dominant mechanism of the OSML turbulent mixing; and evaluate and testify the applicability of boundary layer theories (including the Monin-Obukhov similarity law) and different OSML turbulent mixing models among different ocean weather conditions. The produced relatively universal turbulent structure and ocean mixing parameterizations can be used in the ocean circulation models and would help us to understand the biological environment and biochemical processes, as well as the energy and mass transport, in the upper ocean.

海洋上混合层是大气和海洋内部之间的动量、热量和物质交换的主要通道，而海洋湍流是决定能量和物质输运的关键过程。过去，大多基于数值模拟和室内实验发展出的一系列海洋上混合层湍流参数化模型缺少海洋现场观测的支持和验证。在本项目中，结合常规的海洋湍流、水文和气象观测，主要利用新研发的移动平台精细温度链装置，在不受海况环境的限制下，长时间在南海目标海域开展混合层内湍流混合现场观测。测量的精细温度信号通过极大似然估计方法分析拟合获得湍动能耗散率信息。研究南海上混合层内湍流结构的空间分布和时间变化特征；探讨湍流混合的能量来源和物理机制；评估包括莫宁-奥布霍夫相似理论在内的海洋边界层理论和不同湍流混合参数化模型的适用性。所获得相对普适的海洋混合层参数化方案和湍流结构对于海洋模式和海洋上层的生物环境和生化过程都具有重要指导意义。

海洋上混合层湍流混合对于研究海洋上层物质和能量输运、海气相互作用等有重要意义。在本项目的资助下，采用海洋移动观测平台精细温度链装置，在南海北部开展长时间海洋上混合层的湍流观测；结合海洋湍流的传统观测和水文观测，研究了南海上层湍流混合的分布特征，提出了混合层底部耗散率是混合层耗散率的特征参量，基于其归一化的混合层耗散率具有很好的相似性特征。进一步讨论了混合层底部耗散率与剪切通量和浮力通量之间的影响关系，并提出了新的非线性参数化方案。进一步将海洋上混合层的研究结果推进到海洋底层，研究了海洋底混合层湍流结构特征和对流不稳定对底层湍流混合的贡献等。基于以上研究结果共发表学术论文10篇，其中SCI论文7篇，授权国家专利2项。本项目的研究结果对于理解和认识海洋边界层、以及基于海洋边界层的物质和能量输送有重要意义。