非均匀地表陆气相互作用的理论与参数化

Numerical models today are an irreplaceable tool for weather prediction and climate research. With the recent advent of a new generation of supercomputers, weather forecasting and climate modeling with a horizontal grid spacing of kilometres have now become possible. However, no matter how high the resolution is, the land-atmosphere interactions are always subgrid-scale processes that cannot be explicitly resolved but must be parameterized. The land surface in nature is always more or less heterogeneous. Strong surface heterogeneity can induce significant circulations which in turn dynamically affect surface fluxes of energy, mass, and momentum between land surface and atmosphere. I propose to start a research group that will address the major current unknowns in land-atmosphere interactions. First, we propose to describe land surface heterogeneity in terms of information content and relevant scales. Second, we will develop a new theory framework for the estimate of surface fluxes over heterogeneous surfaces, with surface heterogeneity explicitly taken into account in terms of both information content and relevant scales. Third, we will systematically investigate the relationships between surface heterogeneity, surface fluxes, and turbulence by using the large-eddy simulation technique. Finally, we aim to parameterize the dependence of surface fluxes on the surface heterogeneity, implement the parameterization to mesoscale models and evaluate it.

数值模式是当今进行天气预报和气候研究不可替代的工具。随着超级计算机的迅猛发展，公里级分辨率的数值天气预报及气候模拟逐渐成为可能。然而，不管分辨率多高，陆气交换总是需作参数化处理的次网格过程。自然界的陆地表面总是或多或少非均匀的，地表非均匀性能引起次级环流进而影响陆面与大气之间的能量、物质和动量等的通量交换。本项目拟针对次网格地表非均匀性所产生的次级环流的影响开展理论与参数化研究：1) 基于信息内容和相关尺度对地表非均匀性进行定量表征；2) 为非均匀地表通量的计算发展新的理论框架；3) 利用大涡模拟技术系统考察地表非均匀性、地表通量、以及湍流之间的关系；4) 对地表通量与地表非均匀性的关系进行参数化，并基于中尺度模式对该参数化方案进行评估。

不管分辨率多高，数值模式中的地表湍流交换总是需作参数化处理的次网格过程。自然界的陆地表面总是或多或少非均匀的，地表非均匀性能引起次级环流进而影响陆面与大气之间的能量、物质和动量等的湍流交换。本项目首先发展了一种数据自适应的三维多尺度分析方法OPD。基于此方法和高分辨率大涡模拟数据，提出了一个简单易用的考虑大涡影响的地表湍流交换新方案（其中边界层高度为唯一新增参数），并从多个不同角度对这一方案进行了严格评估，结果显示该方案稳定可靠，简单易用，适用于不稳定条件下的陆面过程模拟。该方案已经应用于我国自主知识产权的陆面过程模式CoLM。本项目还厘清了地表非均匀性与边界层高度之间的关系，揭示了地表非均匀性可以通过影响边界层高度（大涡特征尺度）从而进一步影响地表湍流交换，确定了边界层高度在地表非均匀性影响地表湍流交换过程中的桥梁作用。此外，还对地表湍流通量的可预报性问题进行了系统考察。