复杂下垫面大气湍流各态历经性和低频效应观测实验研究

The observation of atmospheric turbulence over complex underlying surface is a difficult issue encountered currently. Faced with these difficult problems, scientists from various countries have studied from various angles, found that the reasons are complicated, and public opinions are divergent, perplexing, even the conclusion is contrary. In this proposing, two core issues, the ergodicity and low-frequency effects of atmospheric turbulence, are refined from domestic and international as well as numerous and disorderly research on the observation of atmospheric turbulence under the condition of complex underlying surface. The complex terrain in the Loess Plateau as a platform, on the traditional theory combining with the theory of non-equilibrium thermodynamics of atmospheric turbulence, and research on the ergodicity and low-frequency effect of atmospheric turbulence under the complex underlying surface as a breakthrough point, we will try to reveal the atmospheric advection, low frequency effects and the coupling effect of vertical velocity for the underlying surface of thermal and dynamic heterogeneity, as well as these effects being relative to the characteristics of atmospheric turbulence, such as the turbulent spectrum, atmospheric eddy structure and turbulence intensity, and that the transport processes of turbulent fluxes of the sensible heat, latent heat, and CO2. This will lay theoretical fountation for overcoming the dificulties encountered in research on the atmospheric turbulence and land surface processes. As a practic application of subject, studying the characteristics of energy and matter balances of the ecological environment of loess plateau based on the theory of non-equilibrium thermodynamics of atmospheric turbulence provides a reference to protect the ecological environment of loess plateau. This study has important scientific significance and application prospect.

复杂下垫面是当前大气湍流观测遭遇到的困难问题。面对这一困难问题，各国科学家纷纷从各个角度研究，发现原因错综复杂众说纷纭，甚至结论相悖。本项目从国内外纷杂的复杂下垫面大气湍流研究中提炼出大气湍流各态历经性和低频效应两大核心问题。以黄土高原复杂地形为平台，以传统的大气湍流理论与大气湍流非平衡态热力学理论相结合，并以复杂下垫面大气湍流各态历经性和低频效应研究为突破口，揭示动力和热力非均匀复杂下垫面的大气平流、低频效应、垂直速度耦合效应以及它们同大气涡旋结构、湍流谱、湍流强度等大气湍流特性以及大气热通量、水汽通量、CO2通量等输送过程之间的关系。为克服非均匀下垫面大气湍流和陆面过程研究中面临的困难问题奠定理论基础。作为项目的实际应用，在大气湍流非平衡态热力学理论基础上研究黄土高原生态环境条件下能量和物质平衡特征。为黄土高原生态环境保护提供参考依据。该项研究是有重要科学意义和应用前景的。

无论是全球通量网不同区域生态系统以碳通量为核心的能量和物质湍流输送观测，还是目前陆面过程观测都是在复杂下垫面条件下进行的长周期观测。但是近地面层湍流理论的基础是建立在水平均匀和定常条件下的。而且观测资料质量控制的标准除了仪器误差订正之外，都以均匀下垫面为标准剔除非均匀下垫面干扰。在估算地表湍流通量时，涡动相关法经常采用 30 分钟的平均计算协方差，通过二次坐标旋转等方法消除垂直速度，并进行低频修正消除趋势效应。这本质上是以高通滤波提取了短周期高频信号，人为地滤去了地形和热力差异等低频过程信号。为了解决这一矛盾,发展近地面层湍流理论，本项目以黄土高原复杂地形为平台，首先建立了一套修正风速零漂的方法以提高风速的观测精度。在资料分析中，以湍流的各态历经性检验为基础确定湍流观测质量。并利用单点观测和多点观测的各态历经性揭示黄土高原湍流的结构分布特征，并结合湍流结构函数确定区域不同尺度湍流间的能量传递，刻画塬区热力湍流场发展变化特征。这都表明，复杂下垫面上湍流可以满足定常性，但湍流输送是非水平均匀的。因此要想准确计算感热和潜热通量或者地表CO2通量，只能通过全面地湍流结构研究，掌握所有的湍流输送过程，经过对观测高度的湍流通量进行修正，才能最终确定感热和潜热通量或者地面CO2通量，实现地表能量和物质平衡。研究也再次证明垂直速度耦合效应是湍流输送的一种过程。项目还利用GPS探空建立了直接确定高空湍流谱的方法，并利用该方法研究了一个3300~4000m高度的重力波，分析了重力波和湍流间的相互作用。在理论研究方面，项目利用CASES99和黄土高原近地面层资料建立了一个从气候尺度-天气尺度-边界层尺度的湍流全谱。项目的研究成果不但促进了近地面层理论和大气湍流的发展。也拓展了卫星定位系统在高空湍流观测中的应用。