Parameterization Errors in Numerical Simulations of Stably-Stratified Atmospheric Boundary Layers Using CASES-99 Observations

了解大气边界层的动态对于更好地了解天气和气候是至关重要的。利用大涡模拟(LES)技术和中尺度模式对稳定层结大气边界层(ABL)的演变进行了数值研究。这项研究将把数值模拟和最近的野外项目CASE-99的观测结合起来。数值模拟将补充观测，以提供关于稳定边界层(SBL)过程的更详细的信息：湍流输送和动量、热量和水汽的混合。研究的目标是：1)对规范的、强层化的夜间边界层(NBL)进行长期、高分辨率的模拟；2)使用广泛的观测数据库来验证这些模拟的结果；以及3)为大规模模拟开发和测试更精确的SBL参数化。目前大气湍流和近地层参数化的缺陷导致它们不能准确地表示强稳定层化条件下的全球间歇。参数化失败是因为它们无法解释诸如重力波破裂和开尔文-赫姆霍兹波动等非线性效应，这一假设将得到检验。并行大涡模拟和中尺度程序将在大规模并行处理机上使用，以解析从几米(小惯性范围涡旋)到几十公里(含能量涡旋)的所有动态相关运动尺度。将特别注意准确地描述与低空急流有关的重力波和切变之间的相互作用以及发生全球间歇的条件。通过分解很大一部分湍流涡旋和重力波，将有可能减少中尺度模式中湍流参数化所带来的不确定性和偏差。

Understanding the dynamics of the atmospheric boundary layer is crucial to better understanding of both weather and climate. A numerical study of the evolution of a stably stratified atmospheric boundary layer (ABL) will be carried out using a large-eddy simulation (LES) technique and a mesoscale model. This study will combine numerical simulations and observations from a recent field program - CASES-99. Numerical simulations will complement observations in providing more detailed information about stable boundary layer (SBL) processes: turbulence transport and mixing of momentum, heat, and moisture.The goals of the research are: 1) to conduct long-term, high-resolution simulations of canonical, strongly stratified nocturnal boundary layers (NBL); 2) to verify the results of these simulations using an extensive observational data base; and 3) to develop and test more accurate parameterizations of SBLs for large-scale simulations.Underlying deficiencies in current atmospheric turbulence and surface layer parameterizations result in their failure to represent accurately global intermittence under strong stably-stratified conditions. The hypothesis that the failures of parameterization arise from their inability to account for nonlinear effects such as breaking gravity waves and Kelvin-Helmholtz billows will be tested. Parallel LES and mesoscale codes will be used on a massively parallel processor to resolve all the dynamically relevant scales of motion from several meters (small inertial range eddies) to several tens of kilometers (energy containing eddies). Special attention will be given to represent accurately interactions between gravity waves and shear associated with low-level jets and conditions under which global intermittence occurs. By resolving a large fraction of turbulence eddies as well as gravity waves it will be possible to reduce uncertainties and biases introduced by turbulence parameterizations in mesoscale models.