地表湍流通量计算方法的研究综述

地表通量的计算方法主要有：以能量平衡为基础的Bowen比能量平衡法、以相似理论为基础的空气动力学方法以及以精度比较高的观测仪器为基础的涡旋相关法。本文对这些计算方法进行了简单的讨论,并介绍了涡旋相关观测系统原始资料的处理方法及一些物理量修正方案的研究进展。对存在的问题进行了一定的讨论。     

地表湍流通量计算方法的研究综述

地表通量的计算方法主要有:以能量平衡为基础的Bowen比能量平衡法、以相似理论为基础的空气动力学方法以及以精度比较高的观测仪器为基础的涡旋相关法。本文对这些计算方法进行了简单的讨论,并介绍了涡旋相关观测系统原始资料的处理方法及一些物理量修正方案的研究进展。对存在的问题进行了一定的讨论。     

通量-方差法估算沿海近地面层的湍流通量分析

利用通量-方差法,通过确定速度和温度归一化标准差与稳定度之间的变化关系,估算出东南沿海地区的湍流动量通量和感热通量。我们发现在中性条件下 并不像Tillman等认为是常数,而是随稳定度参数按指数形式变化。与涡动协方差相关测量系统测量结果进行比较发现,通量-方差方法估算结果与测量值两者符合得较好,相关性高,动量通量的相关系数为0.87,而感热通量的为0.95。利用该方法估算沿海近地面层的湍流通量具有一定的代表性。     

CO2湍流通量误差的修正和不确定性研究进展

目前国内外对能量和CO₂涡动相关通量的测量误差的谱修正缺乏一致性，导致各测量站之间的资料对比难以进行，给全球尺度资料的合成造成很大困难。因此在强调长期CO₂通量测量精度的同时，还应该注重确定对测量误差修正的首选方法和研究重点。该文主要介绍了两种用于修正测量仪器误差的谱方法；二维和三维的气流运动对通量误差的影响；资料处理中的误差；夜间CO₂通量的测量问题。     

近地层组合法确定湍流通量精度的研究

近地层组合法的实质是将廓线法和地面能量平衡方程联立而计算湍流参数和通量的一种方法。本文利用实测的脉动场和平均场的同步梯度资料研究组合法的精确性及其应用价值。     

非均匀下垫面湍流通量观测的印痕分析

利用2005年在北京昌平区小汤山开展的非均匀下垫面观测实验的观测数据,分别处理了涡旋相关法和大孔径闪烁仪LAS测得的感热通量,并运用印痕模型对数据进行“源区”分析。分析结果表明:在复杂地表上,涡旋相关的测量值由于混杂了其他下垫面的通量信息,不能真实地反映其观测区域的湍流特征,存在着观测误差。而LAS观测出现的低估问题则与掺混高度和“源区”有关。通过用印痕方法进行数据订正后,以上问题均得到很好的改善,订正结果与LAS观测通量的线性关系良好,两者的相关系数达到0.9。实验结果验证了印痕模型在非均匀下垫面的适用性。     

青藏高原东部草甸下垫面涡旋相关观测数据的质量控制及评价研究

目前利用涡旋相关仪观测地表通量的方法已被广泛采用, 但由于涡旋相关法是建立在方程假设简化的基础上, 这对观测数据的质量提出了一定的要求, 所以对观测数据的处理及通量结果的质量状况分析就显得尤为重要。本文以理塘站2006年7月中到8月中的数据为例, 对其进行质量控制, 并将质量控制后的通量计算结果与原始值进行比较。质量控制后感热通量和潜热通量总和有所增长, 动量通量值则受质量控制影响较大。质量评价的结果为:动量通量、感热通量、潜热通量中高质量数据所占比例为68.2%、60.6%、63.3%。     

宁南退耕还草区近地面的湍流通量特征研究

根据Monin—Obukhov相似性理论，运用空气动力学方法和能量平衡法，结合2002—2003年小气候资料，分别分析了宁夏南部山区（下称宁南）退耕还草区湍流通量和地表通量（净辐射、感热、潜热和土壤热通量）的分布和季节变化特征，为宁南退耕还草区陆面过程的认识、数值模拟和气候分析提供理论参考依据。     

应用通量方差法估算戈壁绿洲下垫面湍流通量的研究

利用“绿洲系统能量与水分循环过程观测试验” 2005年绿洲、戈壁点的观测资料, 分析与讨论了温度、水汽的归一化标准差随稳定度变化的通量方差关系, 应用通量方差法对感热、 潜热通量进行了计算, 并同涡动相关系统的观测结果进行了比较。不稳定条件下, 戈壁点温度归一化标准差随稳定度变化的通量方差关系优于下垫面非均匀性更强的绿洲点, 绿洲点水汽的归一化标准差随稳定度变化的通量方差关系较温度量表现得更好。对同一站点, 归一化温度标准差的通量方差关系并不总是优于水汽的通量方差关系, 其取决于该站点的温度以及水汽的源汇分布情况; 通量方差法对两个站点的感热、 潜热通量均有较好的再现, 但戈壁点感热通量的计算效果优于非均匀性更强的绿洲点。应用通量方差法对潜热通量计算时若采用直接观测的感热通量, 则潜热通量的计算效果具有一定程度的改善。     

不同气象条件下湍流通量的研究

利用1989年12月－1990年1月在重庆市测得的三轴风速仪资料和气象资料，1990年7月－8月在天津测得的三轴风速仪资料、温度脉冲资料、气象资料、计算了不同气象条件下的动量通量、热通量、摩擦速度和特征温度。这对了解重庆和天津市郊不同气象条件下的近地面层的湍流通量特征是十分有益的。     

Comparison of Ozone Fluxes over a Maize Field Measured with Gradient Methods and the Eddy Covariance Technique

Ozone(O_3) fluxes were measured over a maize field using the eddy covariance(EC) technique and gradient methods.The main objective was to evaluate the performance of the gradient methods for measuring the O_3 flux by comparing them with the EC O_3 flux.In this study,turbulent exchange coefficients(K) calculated with three methods were compared.These methods were the aerodynamic gradient(AG) method(in which K is calculated by using wind speed and temperature gradients),the aerodynamic gradient combined with EC(AGEC) method,in which the friction velocity and other variables are based on EC measurements,and the modified Bowen ratio using the EC sensible heat flux and temperature gradient(MBR) method.Meanwhile,the effects of the measurement and calculation methods of the O_3 concentration gradient were analyzed.The results showed that:(1) on average,the transfer coefficient computed by the MBR method was 40% lower,and the coefficient determined with the AG method was 25% higher,than that determined with the AGEC method.(2) The gradient method's O_3 fluxes with the MBR,AGEC,and AG methods were 30.4% lower,11.7% higher,and 45.6% higher than the EC O_3 flux,respectively.(3) The effect of asynchronous O_3 concentration measurements on the O_3 gradient must be eliminated when using one analyzer to cyclically measure two-level O_3 concentrations.The accuracy of gradient methods for O_3 flux is related to the exchange coefficient calculation method,and its precision mainly depends on the quality of the O_3 gradient.     

Relaxed Eddy Accumulation Simulations of Aerosol Number Fluxes and Potential Proxy Scalars

Direct eddy-covariance measurements of aerosol number fluxes obtained during the 2007 CHATS field experiment in Dixon, California, USA are compared with relaxed eddy accumulation simulations using temperature and water vapour concentration as proxy scalars. After a brief discussion of the limited time response of the aerosol measurement, the applicability of temperature and water vapour concentration as proxy scalars for aerosol number concentration is investigated by evaluating scalar and spectral correlation coefficients as simple measures of scalar similarity. In addition, the proportionality factor b, which compensates for the use of a constant sampling flow in relaxed eddy accumulation, is derived from the time series of aerosol number, temperature and water vapour, and its variability is analyzed. The reduction of the b factor due to application of a deadband, i.e. the rejection of data when the vertical wind speed is close to zero, is evaluated for all three studied scalars, and compared with published functional relationships. In this study, using temperature or water vapour as proxy scalars for aerosol number shows no advantage over the use of a constant b factor. Thus, it is suggested to apply a deadband H _REA  = w′/σ _w  = 0.6 to 0.8 (where w′ is the vertical velocity fluctuation and σ _w is its standard deviation), to use a theoretical b factor based on a parameterization that includes a stability dependence, and to calculate the deadband effect according to a derived relation for aerosol relaxed eddy accumulation.     

对流边界层中泡状结构的大涡模拟研究

本文提出“连续垂直运动区”的概念，对边界层中的对流泡状运动进行了重新定义。由此将对流边界层划分为上升泡区、下沉泡区和环境气流区，并利用大涡模拟提供的对流边界层数值模拟结果研究这种泡状运动的结构。研究结果较好地解释了一些有关泡状运动结构方面的似乎相互矛盾的观测事实，并揭示了对流泡状运动的一些新的特征。     

Alignment Trends of Velocity Gradients and Subgrid-Scale Fluxes in the Turbulent Atmospheric Boundary Layer

Field experimental data in the atmospheric surface layer are analyzed using toolsfrom statistical geometry. The data consist of velocity measurements from sonicanemometer arrays. In the context of large eddy simulations (LES), these arrayspermit the spatial filtering needed to separate large from small scales. Time seriesof various quantities relevant to LES are evaluated from the data. Results show thatthe preferred filtered fluid deformation is axisymmetric extension and the preferredsubgrid stress state is axisymmetric contraction. The filtered fluctuating vorticityshows preferred alignments with the mean vorticity, with the streamwise direction,and with the intermediate strain-rate eigenvector. The alignment between eigenvectorsof the subgrid-scale stress and filtered strain rate is used to test eddy viscosity andmixed model formulations. In qualitative agreement with prior laboratory measurements at much lower Reynolds numbers, a bimodal distribution is observed, which can be reduced to good alignment with eddy viscosity closure using the mixed model.     

A Re-examination of Density Effects in Eddy Covariance Measurements of CO2 Fluxes

Corrections of density effects resulting from air-parcel expansion/compression are important in interpreting eddy covariance fluxes of water vapor and CO2 when open-path systems are used. To account for these effects, mean vertical velocity and perturbation of the density of dry air are two critical parameters in treating those physical processes responsible for density variations. Based on various underlying assumptions, different studies have obtained different formulas for the mean vertical velocity and perturbation of the density of dry air, leading to a number of approaches to correct density effects. In this study, we re-examine physical processes related to different assumptions that are made to formulate the density effects. Specifically, we re-examine the assumptions of a zero dry air flux and a zero moist air flux in the surface layer, used for treating density variations, and their implications for correcting density effects. It is found that physical processes in relation to the assumption of a zero dry air flux account for the influence of dry air expansion/compression on density variations. Meanwhile, physical processes in relation to the assumption of a zero moist air flux account for the influence of moist air expansion/compression on density variations. In this study, we also re-examine mixing ratio issues. Our results indicate that the assumption of a zero dry air flux favors the use of the mixing ratio relative to dry air, while the assumption of a zero moist air flux favors the use of the mixing ratio relative to the total moist air. Additionally, we compare different formula for the mean vertical velocity, generated by air-parcel expansion/compression, and for density effect corrections using eddy covariance data measured over three boreal ecosystems.     

A Re-examination of Density Effects in Eddy Covariance Measurements of CO_2 Fluxes

Corrections of density effects resulting from air-parcel expansion/compression are important in interpreting eddy covariance fluxes of water vapor and CO2 when open-path systems are used. To account for these effects, mean vertical velocity and perturbation of the density of dry air are two critical parameters in treating those physical processes responsible for density variations. Based on various underlying assumptions, different studies have obtained different formulas for the mean vertical velocity and ...     

一个对流边界层大涡模式的建立与调试

本文介绍一个适合于对流边界层的大涡模式的建立及其调试结果。该大涡模式建立过程中注重于计算的节省，同时也强调原理与方法的简单和合理性。模式的调试表明，对于平坦均一地形的情况，模拟可以获得合理的结果。调试同时显示了模式对较低水平分辨率的适用条件，以及模式应用于模拟较大水平范围问题的可能性。     

关于大气涡动热通量参数化问题研究

用NCEP/NCAR等再分析资料计算和分析表明,月平均瞬变涡动热通量和月平均温度梯度的局域相关性很低,甚至在一些纬度是负相关,更严重的是二者之间存在非线性的多值对应函数关系.如果用非局域参数化,参数化水平将有所提高,但改进并不明显.通过与分子运动论输运理论进行数学、特别是物理类比提出了考虑"风暴路径"效应的瞬变涡动热通量的参数化方案,经再分析资料的检验,结果表明它能大大提高参数化的水平.其次,还证实采用空间非局域参数化仍然是进一步提高瞬变涡动热通量参数化水平的方法之一.此外,资料分析显示中高纬度纬向平均温度梯度和纬偏涡动温度通量之间也存在负相关及多值函数关系,说明仅用温度梯度去参数化纬向平均涡动热通量难以得到好的结果,需要考虑多元参数化或非同步参数化等.     

半干旱区不同下垫面近地层湍流通量特征分析

本文分析了2003～2005年半干旱区退化草地和农田下垫面近地层湍流通量日、季、年的变化特征, 探讨了不同年份的气候背景和下垫面土地覆被对地气交换过程的影响。结果表明: 半干旱区退化草地和农田近地层湍流通量具有明显的日变化、季变化周期; 地气间通量交换年际间的差异主要受当年的气候背景影响, 尤其是降水的影响; 同时还受到下垫面覆被的影响。潜热通量和感热通量的能量分配比率呈反位相变化, 且农田和退化草地的变化趋势相似, 在夏季潜热通量所占比例均超过感热通量; 两种下垫面的波恩比月均值变化趋势十分相似, 量级接近, 夏季低, 春、秋季高; 夏季退化草地和农田下垫面波恩比均小于或等于1。