近地层湍流特征及其在扩散模拟中的应用

利用１９９４年９月北京市郊３２５ｍ气象观测塔在４７ｍ和１２０ｍ两层高度上的湍流观测资料。计算分析了城郊粗糙下垫面上近地层湍流特下量,湍流尺度和不同层结下的湍谱,得出了近地层的一些湍流特性。     

热带沿海近地层大气的湍流结构和谱特征

利用１９９０年在海南省海口市天尾村的一次观测的资料，分析了速度分量谱、湍流强度等湍流特征量。这批资料多是有云影响情况下，稳定度参数（Ｌ）与热通量（ｗｔ）没有日变化规律，但湍能、平均温度仍具有日变化规律；湍谱的基本特征与晴天天气的谱基本相似，在惯性副区接近局地各向同性，速度谱符合相似理论的“－２／３”次方规律；根据Ｍ－Ｏ相似理论，探讨了各分量湍强δｉ／Ｕ＊（ｉ＝ｕ，ｖ，ｗ）与稳定度Ｚ／Ｌ的关系，表明各分量湍强与稳定度Ｚ／Ｌ仍具有“１／３”次方规律，但湍强和湍流能量比一般平坦地形下垫面的大     

天津市郊大气边界层湍谱特征分析

用１９９０年７月在天津市郊的观测资料，计算了风速谱、温度谱及动量和热量通量的协谱。结果表明，市郊下垫面上的大气湍流谱特征与平坦地形上得到的典型结果基本一致，但满足各向同性的湍流尺度似乎比在平坦地形上的略大，谱的峰值频率区域略窄，谱的低频区（含能区）特征与平坦地形上的情况也不同。     

长江三角洲常熟地区近地层湍流特征的研究

利用1999年5－9月长江三角洲常熟地区的湍流脉动观测资料，分析了该地区感热，潜热和动量通量的日变化以及湍流强度和湍流谱特征，结果表明：该地区各能量的日变化与常见情况相同，白天潜热通量的输送占主导地位，感热通量比潜热小得多，且湍流的日变化与天气的关系非常密切，晴天比阴天要大得多。湍流强度和湍流谱的分析结果表明，在近中性条件下，常熟地区各方向湍流强度接近典型平坦下垫面的值。非中性条件下，垂直方向规一化标准差与稳定度的关系都较好地满足1／3次幂定律，水平方向没有垂直方向上的规律好，特别是稳定条件下，数据点分散性大；各风速分量变在高频段满足理论上的－2／3次幂定律，纵向和垂直方向速度谱的峰值频率与典型平坦下垫面上的结果一致，总体输送系数CD，CH与稳定度的关系密切，随稳定度增加有减小的趋势。     

重庆市区冬季小风条件下近地面层某些湍流特征量的分析

利用１９８９年１２月１６日－１９９０年１月１４日在重庆市用三轴风速仪所测得的风速资料，计算了小风条件下重庆近地面层的湍流参数，欧拉时间自相关系数，湍流时间积分尺度，湍流强度，摩擦速度，湍流应力等湍流特征量，以了解重庆地区小风条件下的近地面层的湍流场特征。     

沿海地区大气边界层扩散特征探讨

利用辽东湾近地层三轴风速仪资料分别计算不同稳定度的大气扩散参数及湍流强度。并将不同情况下的大气扩散参数及湍流强度进行了比较。结果表明：在地形相对平坦的辽东湾,在不同的稳定度下,σy和σx值均略大于同级布里格斯公式的计算值。在不稳定条件(C、B类)下,湍强值重大。     

HUBEX试验区近地面层的湍流输送

1998年淮河流域能量和水循环试验(HUBEX)期间曾进行了1个月的近地面层湍流观测.分析不稳定条件下湍流的统计特性和谱特征,并与Monin-Obukhov相似理论进行了比较.结果表明,不稳定的时候各湍流量的统计特征与相似理论的预期相符.虽然不稳定条件下温度和湿度涨落的相关系数很高,谱的式样也相近,但湿度谱的峰值频率高于温度谱.协谱曲线的形状显示感热通量的谱峰较宽,表现出w和T在较宽范围的强相关性,而水汽通量谱在高频段下降很快,说明水汽的输送更多地出现在低频部分.从谱相关系数可见,在近中性的时候,各尺度湍流涡的热量输送效率普遍较低,随着不稳定性增强而显著提高.分析还发现,不论不稳定性的程度如何,小尺度湍流的水汽输送效率都较低.水汽通量谱的相关系数随稳定度的变化不如热通量的谱相关系数大,表明近中性时除小尺度湍流外其他湍流涡的水汽输送效率高于热量输送.     

不同天气条件下城郊近地层湍流谱的研究

利用１９９０年夏季天津市郊观测塔三分量风资料，研究了正常天气和天气过程中近地面湍流谱的一些特征。结果表明，正常天气时，城郊的湍流谱和平坦地形的基本一致，而有天气过程时，湍流谱反映出一些特殊性。文章还讨论了出现这些特殊性的可能原因。     

沿海地区大气边界层扩散特征探讨

利用辽东湾近地层三轴风速仪资料分别计算不同稳定度的大气扩散参数及湍流强度。并将不同情况下的大气扩散参数及湍流强度进行了比较。结果表明 :在地形相对平坦的辽东湾 ,在不同的稳定度下 ,σy 和σz值均略大于同级布里格斯公式的计算值。在不稳定条件 (C、B类 )下 ,湍强值最大。     

我国草原下垫面低层大气湍流结构

利用超声风速仪资料分析了科尔沁草原下垫面低层大气的湍流谱结构，无量纲化湍流速度分量及温度脉动的标准偏差，和湍流通量与稳定度参数的关系。结果表明，草原下垫面低层大气湍流速度谱，在较宽的稳定度范围内， 符合Kolmogorov 相似理论，在惯性副区接近局地各向同性，无量纲化湍流速度分量及温度脉动的标准偏差服从A(1-Bζ)1/3和A(-ζ)-1/3规律， 湍流热通量与稳定度参数ζ存在较好的相关性。     

SPECTRAL CHARACTERISTICS OF SURFACE-LAYER TURBULENCE OVER THE SUBURBS OF TIANJIN

The paper computed the spectra of velocity and temperature,and the cospectra of velocity and temperature by theobservational data of July,1990 in the suburbs of Tianjin.The results show that the characteristics of the atmosphericturbulence spectra over the suburbs are basically in accordance with some typical results over the flat terrain.But thescale,on which turbulence can satisfy the isotropic condition,over the suburbs is larger than over the flat terrain.Thespectrum peak frequency range is a bit narrower.The feature of the spectrum range in low frequency(LF)is out ofaccordance with that of the flat terrain either.     

SPECTRAL CHARACTERISTICS OF SURFACE-LAYER TURBULENCE OVER THE SUBURBS OF TIANJIN*

The paper computed the spectra of velocity and temperature,and the cospectra of velocity and temperature by the observational data of July,1990 in the suburbs of Tianjin.The results show that the characteristics of the atmospheric turbulence spectra over the suburbs are basically in accordance with some typical results over the flat terrain.But the scale,on which turbulence can satisfy the isotropic condition,over the suburbs is larger than over the flat terrain.The spectrum peak frequency range is a bit narrower.The feature of the spectrum range in low frequency(LF) is out of accordance with that of the flat terrain either.     

Attached Eddies and Production Spectra in the Atmospheric Logarithmic Layer

We investigate the production components of turbulent spectra within logarithmic layers over flat ground. This assumes that the turbulence giving rise to these spectra consists of active coherent structures (eddies) that are attached to the ground, and whose properties display perfect statistical self-similarity under inner scaling. That is, we take the extreme view that active coherent structures not only contribute to turbulence production spectra but explain the whole of them, so that neither detached eddies nor unstructured motions make any significant contribution. Perfect self-similarityis held to apply only to eddies that are themselves formed totally within the log layer, so the theory applies in the limit of spectra obtained at the hearts of very deep log layers. The model predicts that spectral variance and covariance should become independent of wavenumber at small wavenumbers. This asymptotic behaviour is observed in all neutral spectra from the Kansas experiment. The model also interprets the various positions of the spectral peaks observed at Kansas and in aircraft flights over the sea as consequences of the eddies being aggregated into files aligned with the wind. The observed spectra are therefore consistent with large-scale wedge-like structures being the principal component of active turbulence in the neutral atmospheric surface layer.     

Spectrum Analysis of Wind Profiling Radar Measurements

Unlike previous studies on wind turbulence spectrum in the planetary boundary layer, this investigation focuses on high-altitude （1-5 km） wind energy spectrum and turbulence spectrum under various weather conditions. A fast Fourier transform （FFT） is used to calculate the wind energy and turbulence spectrum density at high altitudes （1-5 km） based on wind profiling radar （WPR） measurements. The turbulence spectrum under stable weather conditions at high altitudes is expressed in powers within a frequency range of 2 × 10-5-10-3 s-1, and the slope b is between -0.82 and -1.04, indicating that the turbulence is in the transition from the energetic area to the inertial sub-range. The features of strong weather are reflected less obviously in the wind energy spectrum than in the turbulence spectrum, with peaks showing up at different heights in the latter spectrum. Cold windy weather appears over a period of 1.5 days in the turbulence spectrum. Wide-range rainstorms exhibit two or three peaks in the spectrum over a period of 15-20 h, while in severe convective weather conditions, there are two peaks at 13 and 9 h. The results indicate that spectrum analysis of wind profiling radar measurements can be used as a supplemental and helpful method for weather analysis.     

The Characteristics of Turbulence Structure and Transfer over the Middle Area of the Tibetan Plateau

In this paper, turbulent data obtained from the Damxung site during the Secondary Tibetan Plateau Science Experiment (TIPEX) in 1998 are used to study the characteristics of the turbulent spectra, turbulence transport, and the dissipation rates of turbulent kinetic energy, temperature variance, and humidity variance in the middle area of the Tibetan Plateau. The turbulent spectra of wind velocity, potential temperature, and humidity satisfy the-2/3 power law in the high frequency range. Horizontal transportation of heat and water vapor is negligible compared with vertical transportation under strong unstable conditions, and as the stability parameter z/L increases (where z is the observational height, and L is the Monin Obukhov length), horizontal transportation becomes dominant under near-neutral, neutral, and stable conditions. The non-dimensional temperature and humidity variances are 20% less than the temperature and humidity gradient variances. These deficits appear to increase as the absolute stability parameter increases. Moreover, the effects of turbulence transportation and pressure variance exist throughout the entire stability region.     

Spectra of surface wind speed and air temperature over the ocean in the mesoscale frequency range in JASIN-1978

Based on the data from an array of buoys during the JASIN-1978 field experiment made in an area northwest of Scotland, power spectra of surface wind speed and air temperature over the ocean in the mesoscale frequency range were studied. The averaged composite spectrum of wind speed for the whole period shows the existence of a spectral gap in the frequency range from 10^–4 to 5 × 10^–3 Hz. However, significant peaks in this range are often seen in particular spectra under certain weather conditions. Mesoscale spectral peaks of wind speed occur in 14 segments of the data record, approximately 10% of the total duration of the observations. In 4 of these segments, the mesoscale spectral peaks of both wind speed and air temperature occurred simultaneously. Several wave patterns of mesoscale atmospheric disturbances when mesoscale spectral peaks were seen are derived from phase differences between buoys. Significant mesoscale peaks in spectra appear in relatively strong winds and unstable or near-neutral atmospheric conditions, and none in stable atmospheric conditions. A criterion of wind speed and atmospheric stability is found for the mesoscale spectral peak appearance.     

Turbulence Statistics Measurements in a Northern Hardwood Forest

Tower-based turbulence measurements were collected in and over a mixed hardwood forest at the University of Michigan BiologicalStation (UMBS) UMBSflux site in the northern summerof 2000. Velocity and temperature fluctuations were measured at five levels within the canopy (up to the canopy height, H = 21.4 m), using one- and three-dimensional sonic anemometers and fine-wire thermocouples. Six additional thermocouples were distributed over the canopy-layer depth. Three-dimensional velocities and sonic temperatures were also measured above the canopy at 1.6H and at 2.15H on the AmeriFlux tower located at the UMBSflux site. Vertical profiles of buoyancy flux, mean horizontal velocity, Reynolds stress, and standard deviation and skewness of velocity components were calculated. The analysis of these measurements aims at a multi-layer parameterization framework of turbulence statistics forimplementation in Lagrangian stochastic models. Turbulence profiles and power spectra above the canopy were analyzed in the context of Monin-Obukhov similarity theory (MOST) and Kolmogorov theory, as determined by stability at the top level (2.15H), to assess the extent to which surface scaling is valid as the canopy top is approached. Velocity spectra were computed to explore the potential of estimating the viscous dissipation rate, and results show that the high frequency range of the spectra above the canopy exhibits the roll-off predicted by Kolmogorov theory. Similarly, velocity standard deviations above the canopy converge to MOST predicted values toward the top level, and spectral peaks shift with stability, as expected. Within the canopy, both turbulence statistics profiles and spectral distributions follow the general known characteristics inside forests.     

Turbulence in Waving Wheat

Measurements of mean and fluctuating velocities, surface pressure and stalk waving have been made in a uniform wheat canopy. Features of the vertical profiles of mean turbulence quantities are discussed in the context of the resonant waving of wheat stalks. The discrete and prominent peaks in the velocity spectra measured in and above the canopy are then analyzed in the light of the organized travelling wave-type structure or ‘honami’, observed in such crops on windy days. Prominent peaks in the spectra are identified with the arrival of gusts, the stalk-waving frequency, and the frequency of oscillations in canopy height. Two possible mechanisms are proposed to account for the observed height dependence of the peak frequencies, directly associated with stalk waving.     

Turbulence in waving wheat

Measurements of mean and fluctuating velocities, surface pressure and stalk waving have been made in a uniform wheat canopy. Features of the vertical profiles of mean turbulence quantities are discussed in the context of the resonant waving of wheat stalks. The discrete and prominent peaks in the velocity spectra measured in and above the canopy are then analyzed in the light of the organized travelling wave-type structure or ‘honami’, observed in such crops on windy days. Prominent peaks in the spectra are identified with the arrival of gusts, the stalk-waving frequency, and the frequency of oscillations in canopy height. Two possible mechanisms are proposed to account for the observed height dependence of the peak frequencies, directly associated with stalk waving.