高阶闭合云参数化的研发及其在东亚的适用性

Higher-Order Closure cloud scheme (HOC) unifies shallow convection, boundary layer and startifrom clouds, that is a frontier field of physics processes. The future high-resolution models will resolve deep convection, however, the boundary layer turbulence and boundary layer cloud features will be still grossly underresolved that must be parameterized. In current large-scale models and cloud-resolving models, boundary layer turbulence and shallow convection are described by different and separate schemes, however such treatments are somewhat artificial and unrealistic, since cloud regimes and physic processes are inextricably interconnected. It thus suggests the development of so-called unified parameterizations, i.e. HOC, to better represent varied cloud regimes and their interactions. However, today’s HOC is lacking in simulating the interaction between boundary layer turbulence and boundary layer cloud, because of the low vertical model resolution. It still has parametric uncertainty, because many of its parameters cannot be derived theoretically. Also, it needs to be evaluated its applicability in East Asian, as HOC was just applied in climate model in the last few years. In order to solve these above questions, this project will improve the HOC by considering the interaction of boundary layer turbulence and boundary layer cloud; analyze the its parametric sensitivities in the simulation of East Asian Summer Monsoon through uncertainty quantification technique; calibrate the key processes based on Chinese observation data, which finally improves the applicability of HOC in East Asian.

云参数化是模式研发的难点之一。未来模式将达到深对流解析，而尺度更小的边界层、浅对流等过程仍需被参数化描述。当前气候模式和云解析模式多采用分离的参数化描述它们，但由于云动力特征频繁的转换和相互作用，分离参数化并不符合自然规律。因此，发展高阶闭合云参数化（HOC）统一边界层、浅对流和层云过程，逐渐成为模式发展的前沿问题。但受制于模式较粗的垂直分辨率，HOC在描述云和边界层次网格过程相互作用方面还不完善；HOC非常复杂，其中一些过程无法求得解析解，尚存在不确定性；HOC在东亚地区的适用性尚属研究空白。因此，本项目以发展完善HOC、提升其在东亚地区的适用性为目标，围绕上述三个问题展开研究：完善HOC中云长波冷却效应对边界层次网格过程的反馈；应用成熟高效的采样方法和敏感性分析法，定量分析和理解HOC模拟东亚夏季风时的参数不确定性；结合中国的场站观测资料，优化核心参数过程减少不确定性，提高其在东亚的适用性。

高阶湍流闭合云参数化能统一湍流、对流、云宏观物理，得益于其物理上高度的一致性，高阶湍流闭合云参数化已经成模式研发的前沿问题。本项目基于数学推导、卫星资料和数值模拟相结合，对高阶闭合云参数化的研发及提高其在东亚地区的适用性开展了系统研究。主要进展如下： .1）基于数学推导，发展了一个“云顶辐射-浮力”机制，其完善了高阶闭合云参数化对云和湍流相互作用的描述，有效地提高了气候模式和单柱模式对副热带湍流和低云的模拟能力；2）基于数学推导和大涡模拟，指出经典湍流尺度的局限性，并提出了“多湍流尺度机制”改进了高阶闭合云方案中气压项和耗散项的求解，显著改进了浅对流和层积云的模拟；3）利用卫星资料评估了气候模式对东亚地区层云的宏观特征对提高低云模拟提供了依据；4）开展高阶闭合云方案的参数扰动试验，揭示了云辐射反馈模拟的参数依赖性，指出参数主要通过气候态低云模拟和“beta”效应来影响对云反馈的模拟；5）开展高阶闭合云方案的有限区域参数扰动试验，指出局地参数贡献对气候模拟起主要作用，而非局地参数贡献主要通过影响绝热加热影响全球气候；6）得益于“云辐射-浮力”机制的引入和参数调整，本项目较大程度提高了高阶闭合云参数化在东亚的适用性，显著改进了东亚地区高、低空大气环流，乃至东亚夏季风降水。.本项目的实施结合理论推导、观测资料分析到数值模拟研究，完善了高阶湍流闭合云参数化，并显著提升了其在东亚地区的适用性。项目成果为模式研发、湍流参数化理论和降低气候预估不确定性提供了必要的理论依据，并具有较好的应用价值。