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1.
Mitsuaki Horiguchi Taiichi Hayashi Ahoro Adachi Shigeru Onogi 《Boundary-Layer Meteorology》2012,144(2):179-198
Large-scale turbulence structures in the near-neutral atmospheric boundary layer (ABL) are investigated on the basis of observations made from the 213-m tall meteorological tower at Tsukuba, Japan. Vertical profiles of wind speed and turbulent fluxes in the ABL were obtained with sonic anemometer-thermometers at six levels of the tower. From the archived data, 31 near-neutral cases are selected for the analysis of turbulence structures. For the typical case, event detection by the integral wavelet transform with a large time scale (180 s) from the streamwise velocity component (u) at the highest level (200 m) reveals a descending high-speed structure with a time scale of approximately 100 s (a spatial scale of 1 km at the 200-m height). By applying the wavelet transform to the u velocity component at each level, the intermittent appearance of large-scale high-speed structures extending also in the vertical is detected. These structures usually make a large contribution to the downward momentum transfer and induce the enhancement of turbulent kinetic energy. This behaviour is like that of “active” turbulent motions. From the analysis of the two-point space–time correlation of wavelet coefficients for the u velocity component, the vertical extent and the downward influence of large-scale structures are examined. Large fluctuations in the large-scale range (wavelet variance at the selected time scale) at the 200-m level tend to induce the large correlation between the higher and lower levels. 相似文献
2.
高风速相干结构对通量输送影响的实验研究 总被引：2，自引：0，他引：2
切变湍流的相干结构是湍流研究中的重大发现,它表明湍流运动并非完全随机,其中具有可检测的有序结构.本文通过处理南京浦口地区大气边界层观测数据,来分析不稳定层结中高风速相干结构特征.本次观测项目包括对场地中央的气象铁塔上2 m和40 m高度上超声风速仪的脉动速度、温度测量以及风廓线雷达对边界层风速廓线的测量.对超声水平风速时间序列数据进行小波变换 (时间尺度400 s),通过阈值来识别这种高风速相干结构.与多普勒风廓线雷达测量结果对比后发现,这种方法确定的相干结构符合常规的认识,具有较长的时间尺度和较大的垂直尺度 (接近边界层厚度).分析三天相干结构特性得到无量纲空间间隔约为6,即每隔6个边界层厚度的水平位置出现一个高速相干结构.通过与垂直风速小波系数的比较,发现高风速相干结构与向下垂直风速之间有较好相关,这与湍流中 “阵风” 现象的研究结论相似.使用四象限分析方法分类得到两种动量通量输送为负的运动:较小水平风速的上扬 (ejection) 运动 (简称为上扬运动) 和较大水平风速的下扫 (sweep) 运动 (简称为下扫运动),这两种运动在整个湍流活动中处于主导地位.高风速相干结构通过促进下扫运动和抑制上扬运动来影响动量通量的输送. 相似文献
3.
Mitsuaki Horiguchi Taiichi Hayashi Ahoro Adachi Shigeru Onogi 《Boundary-Layer Meteorology》2014,151(2):221-237
Based on the analysis of observations from a 213-m tall meteorological tower at Tsukuba, Japan, we have investigated the favourable conditions for the predominant existence of large-scale turbulence structures in the near-neutral atmospheric boundary layer (ABL). From the wavelet variance spectrum for the streamwise velocity component ( $u$ ) measured by a sonic anemometer-thermometer at the highest level (200 m), large-scale structures (time-scale range of 100–300 s) predominantly exist under slightly unstable and close to neutral conditions. The emergence of large-scale structures also can be related to the diurnal evolution of the ABL. The large-scale structures play an important role in the overall flow structure of the lower boundary layer. For example, $u$ velocity components at the 200-m and 50-m levels show relatively high correlation with the existence of large-scale structures. Under slightly unstable (near-neutral) conditions, a low-speed region in advance of the high-speed structure shows a positive deviation of temperature and appears as the plume structure that is forced by buoyancy in the heated lower layer. In spite of the difference in buoyancy effects between the near-neutral and unstable cases, large-scale structures are frequently observed in both cases and the same vertical correlation of $u$ components is indicated. However, the vertical wind shear is smaller in the unstable cases. On the other hand, in near-neutral cases, the transport efficiency of momentum at the higher level and the flux contribution of sweep motions are larger than those in the unstable cases. 相似文献
4.
During the CASES-99 field experiment, three quartz-based microbarographs were installed on the 58-m main tower at the Central Site. These devices measuredabsolute pressure with temperature compensated output at a resolution better than 0.2 Pa and a sampling frequency of 2 s-1 during the whole campaign. This sampling rate is not adequate to compute turbulent pressure fluxes with the classic averaging method, but the wavelet transform allows flux estimations at a wide range of scales. The resolution of the devices is suitable to study pressure perturbations such as internal gravity waves. The night period of the Intensive Operational Period number 6 (IOP6), where wave-like structures were present, is chosen to illustrate the method. A complete wavelet analysis of pressure recordsand data from sonic anemometers located at the same heights in the tower is performed. Wavelet methods make it possible to identify the relevant scales in the flowand to study the vertical structure of pressure perturbations, including coherent structures and small-scale motions.A study of a simplified turbulence kinetic energy budget equation is made and the contribution of the pressure terms is discussed. 相似文献
5.
Igor Petenko Giangiuseppe Mastrantonio Angelo Viola Stefania Argentini Ilaria Pietroni 《Boundary-Layer Meteorology》2012,143(1):125-141
Some characteristics of wavelike motions in the atmospheric boundary layer observed by sodar are considered. In an experiment
carried out in February 1993 in Milan, Italy, Doppler sodar measurements were accompanied by in situ measurements of temperature
and wind velocity vertical profiles using a tethered balloon up to 600 m. The oscillations of elevated wavy layers containing
intense thermal turbulence, usually associated with temperature-inversion zones, were studied by using correlation and spectral
analysis methods. The statistics of the occurrence of wavelike and temperature-inversion events are presented. The height
distributions of Brunt–Vaisala frequency and wind shear and their correlation within elevated inversion layers were determined,
with a strong correlation observed between the drift rate of the wavy layers and the vertical velocity measured by Doppler
sodar inside these layers. Spectral analysis showed similarities regarding their frequency characteristics. The phase speed
and propagation direction of waves were estimated from the time delay of the signals at three antennae to provide estimates
of wavelength. Moreover, wavelengths were estimated from the intrinsic frequency obtained from sodar measurements of the Doppler
vertical velocity and oscillations of wavy turbulent layers. The two wavelength estimates are in good agreement. 相似文献
6.
Summary ?Progress in technology as well as signal processing has promoted Wind Profiler Radar (WPR) or sodar with RASS additions to become standard tools in profiling of the atmospheric boundary layer. Apart from
these instruments’ basic abilities in profiling mean winds and temperature, this paper will give an emphasis on the profiling
of ABL height as well as the turbulent fluxes of sensible heat and momentum both, with respect to methods as well as with
respect to realization. The special focus will thereby be laid on the demands for vertical profiling, which were defined within
the LITFASS-project of the German Meteorological Service. In the frame of this project, some special measuring campaigns have
been performed where remote-sensing systems were used to assess their abilities in profiling ABL parameters. On the base of
some case studies from these campaigns comparisons are shown, where results from sodar/RASS and WPR/RASS measurements are
compared to measurements from airborne sensor systems and results from numerical models. Regarding turbulent heat fluxes,
we found excellent agreement for remotely-sensed flux profiles from WPR/RASS with both, numerical models and airborne in-situ
measurements. However, as the inherent errors of the remotely-sensed fluxes are in the order of ± 20 ⋯ 30 W/m2 typically, current signal processing does not allow to interpret small-scale vertical structures in the profiles with respect
to surface inhomogeneities yet.
Received June 16, 2001; revised February 20, 2002; accepted May 30, 2002 相似文献
7.
Christian Barthlott Philippe Drobinski Clément Fesquet Thomas Dubos Christophe Pietras 《Boundary-Layer Meteorology》2007,125(1):1-24
A long-term study of coherent turbulence structures in the atmospheric surface layer has been carried out using 10 months
of turbulence data taken on a 30-m tower under varying meteorological conditions. We use an objective detection technique
based on wavelet transforms. The applied technique permits the isolation of the coherent structures from small-scale background
fluctuations which is necessary for the development of dynamical models describing the evolution and properties of these phenomena.
It was observed that coherent structures occupied 36% of the total time with mean turbulent flux contributions of 44% for
momentum and 48% for heat. The calculation of a transport efficiency parameter indicates that coherent structures transport
heat more efficiently than momentum. Furthermore, the transport efficiency increases with increasing contribution of the structures
to the overall transport. 相似文献
8.
Coherent Structures and the Dissimilarity of Turbulent Transport of Momentum and Scalars in the Unstable Atmospheric Surface Layer 总被引：7，自引：7，他引：0
Atmospheric stability effects on the dissimilarity between the turbulent transport of momentum and scalars (water vapour and
temperature) are investigated in the neutral and unstable atmospheric surface layers over a lake and a vineyard. A decorrelation
of the momentum and scalar fluxes is observed with increasing instability. Moreover, different measures of transport efficiency
(correlation coefficients, efficiencies based on quadrant analysis and bulk transfer coefficients) indicate that, under close
to neutral conditions, momentum and scalars are transported similarly whereas, as the instability of the atmosphere increases,
scalars are transported increasingly more efficiently than momentum. This dissimilarity between the turbulent transport of
momentum and scalars under unstable conditions concurs with, and is likely caused by, a change in the topology of turbulent
coherent structures. Previous laboratory and field studies report that under neutral conditions hairpin vortices and hairpin
packets are present and dominate the vertical fluxes, while under free-convection conditions thermal plumes are expected.
Our results (cross-stream vorticity variation, quadrant analysis and time series analysis) are in very good agreement with
this picture and confirm a change in the structure of the coherent turbulent motions under increasing instability, although
the exact structure of these motions and how they are modified by stability requires further investigation based on three-dimensional
flow data. 相似文献
9.
A diagnostic study of heat transfer within the lower atmosphere and between the atmosphere and the surface of the Arctic Ocean
snow/ice pack during clear-sky conditions is conducted using data from the Surface Heat Budget of the Arctic Ocean (SHEBA)
field experiment. Surface heat budgets computed for four cloudy and four clear periods show that, while the net turbulent
heat fluxes at the surface are small during the cloudy periods, during the clear-sky periods they are a considerable source
of surface heating, balancing significant portions of the conductive heat fluxes from within the snow/ice pack. Analysis of
the dynamics and thermodynamics of the lower atmosphere during the clear-sky periods reveals that a considerable portion of
the heat lost to the surface by turbulent heat fluxes is balanced by locally strong heating near the atmospheric boundary-layer
(ABL) top due to the interaction of subsiding motions with the strong overlying temperature inversions surmounting the ABL.
This heat is then entrained into the ABL and transported to the surface by turbulent mixing, maintained by a combination of
vertical wind shear and wave-turbulence interactions. The frequency of stable, clear-sky periods, particularly during the
winter, combined with these results, suggests that the downward transfer of heat through the lower atmosphere and into the
surface represents an important component of the heat budgets of the lower atmosphere and snow/ice pack over the annual cycle 相似文献
10.
Stefania Argentini Giangiuseppe Mastrantonio Igor Petenko Ilaria Pietroni Angelo Viola 《Boundary-Layer Meteorology》2012,143(1):177-188
Measurements in the atmospheric surface layer are generally made with point sensors located in the first few tens of metres.
In most cases, however, these measurements are not representative of the whole surface layer. Standard Doppler sodars allow
a continuous display of the turbulent thermal structure and wind profiles in the boundary layer up to 1000 m, with a few points,
if any, in the surface layer. To overcome these limitations a new sodar configuration is proposed that allows for a higher
resolution in the surface layer. Because of its capabilities (echo recording starting at 2 m, echo intensity vertical resolution
of approximately 2 m, temporal resolution of 1 s) this sodar is called the surface-layer mini-sodar (SLM-sodar). Features
and capabilities of the SLM-sodar are described and compared with the sodar. The comparison of the thermal vertical structure
given by the SLM-sodar and the sodar provides evidence that, in most cases, the surface layer presents a level of complexity
comparable to that of the entire boundary layer. Considering its high vertical resolution, the SLM-sodar is a promising system
for the study of the nocturnal surface layer. The nocturnal SLM-sodar measurements have shown that, depending on wind speed,
the structure of the surface layer may change substantially within a short time period. At night, when the wind speed is greater
than 3 m s−1, mechanical mixing destroys the wavy structure present in the nocturnal layer. Sonic anemometer measurements have shown that,
in such cases, also the sensible heat flux varies with height, reaching a peak in correspondence with the wind speed peak.
Under these conditions the assumption of horizontal homogeneity of the surface layer and the choice of the averaging time
need to be carefully treated. 相似文献
11.
This study examines the intermittency of the momentum flux near the surface and the relation of such intermittency to coherent structures. Toward this goal, variances and covariances are decomposed into coherent structures and less coherent activity. The sampled structures are identified using the Haar transform and then decomposed into eigenvectors of the lagged covariance matrix.The methodology is applied to the momentum flux for a relatively stationary 50-h period of strong winds measured from a 45 m tower in the Lammefjord Experiment. Events of sinking motion with strong horizontal momentum account for the majority of the flux. Such sweeping motions arrive as gust microfronts. The large momentum flux is associated with strong coherent fluctuations of the longitudinal wind component and high correlation with relatively modest fluctuations of vertical motion. In the heated case (HAPEX), a phase lag between the vertical and horizontal velocity fluctuations leads to less efficient momentum transport by the main coherent structures.The event nature of the flux is used to formulate an expression for the flux error due to sampling problems. Estimation of the momentum flux requires a significantly longer record than for the heat flux. Modulation of the flux by mesoscale variations also affects the sampling strategy. 相似文献
12.
Well-developed low speed and high temperature streaks in association with the alignment of convection cells are observed in a large-eddy-simulation (LES) generated strongly sheared convective boundary-layer flow, which is driven by a geostrophic wind speed of 15 m s-1 and a surface kinematic heat flux of 0.05 K m s-1. Vortices that drive streaky structures are identified through an eigenvalue method (lambda;2method) near the surface. These vortices are highly elongated along the quasi-streamwise direction alternating sign of the x-component of vorticity (x). By conditional sampling of fully developed vortices, a statistically significant coherent structure is educed. The educed vortex is elongated to the streamwise direction with the elevation angle of about 17° above the horizontal surface. However, the horizontal tilting is not clearly demonstrated in the present simulation. Fluctuation fields in the domain of the educed vortex show the existence of a low speed and high temperature streak as a direct consequence of momentum and heat transport by vortical motions. The strong ejection(upward transport of low momentum or high temperature)occurring at the higher level than that of the strong sweep (downward transport of high momentum and low temperature) can be explained from the spatial distribution of the fluctuationfields of velocity and temperature. The contribution of ejection to the Reynolds stress at z/h1 = 0.18 is about 75%, which is slightly greater than that (70% at z/h1 = 0.173) for the neutrally stratified atmospheric boundary layer. Ejection is also found to be dominant for the turbulent heat flux. 相似文献
13.
Yoshiki Ito 《Boundary-Layer Meteorology》1997,85(3):379-390
Observations from a new five-beam phasedarray Doppler sodar located over a small islandrevealed the development of an internal boundary layer (IBL)from the edge of a cliff in strong windcases, and the presence of systematic convective motions in unstableconditions. The top of the IBL ischaracterized by a small wind maximum trailing fromthe strong wind area at the edge of the cliff, anddevelops with distance from the edge. In the presence ofcumulus clouds, an upwardvelocity region, surrounded by downward motion, wasobserved in the subcloud layer. Anupward convective pattern of organized motion following the passage of cumulus clouds may be young thermalsrising from a height of about 100 m. 相似文献
14.
Taiichi Hayashi 《Boundary-Layer Meteorology》1994,70(3):307-326
A wavelet analysis can supply information of both the location (time) and the scale of fluctuations. This method is applied to the fluctuations of the natural wind and the turbulent transport of momentum in the atmospheric surface layer. The shapes of both the wavelet spectra and the Fourier spectra of the three components of the wind velocity fluctuations are similar to each other. The quadrant representation of momentum transport shows the scale difference of the transport. The large-scale fluctuations mainly contribute to the downward transport of momentum. 相似文献
15.
We describe a wavelet-based technique to determine the spectral turbulentcontribution to the vertical flux of sensible heat in a position-wavelength representation. This technique combines awavelet transform (Morlet wavelet) with conditional sampling. We apply this methodto aircraft datacollected during a sea-breeze circulation (BEMA97 experiment) with heterogeneousturbulence conditions horizontally and vertically as well. The turbulent fluxes are analysed with the conditional wavelet techniqueas a function of the wavelength and the horizontal distance.The turbulent processes within the thermal internal boundary layer associatedwith the sea breeze are clearly identified. The results exhibit the wavelength bands through which the upward flux (originating fromthe surface) and the downward flux (originating from the top of theboundary layer) are important. 相似文献
16.
An atmospheric surface-layer (ASL) experiment conducted at a meteorological site in the Oostelijk-Flevoland polder of the Netherlands is described. Turbulent fluctuations of wind velocity, air temperature and static pressure were measured, using three 10 m towers.Simultaneous turbulent signals at several heights on the towers were used to investigate the properties of the turbulent structures which contribute most significantly to the turbulent vertical transports in the unstable ASL. These turbulent structures produce between 30 and 50% of the mean turbulent vertical transport of horizontal alongwind momentum and they contribute to between 40 and 50% of the mean turbulent vertical heat transport; in both cases this occurs during 15 to 20% of the total observation time.The translation speed of the turbulent structures equals the wind speed averaged over the depth of the ASL, which scales on the surface friction velocity. The inclination angle of the temperature interface at the upstream edge of the turbulent structures to the surface is significantly smaller than that of the internal shear layer, which is associated with the temperature interface. The turbulent structures in the unstable ASL are determined by a large-scale temperature field: Convective motions, which encompass the whole depth of the planetary boundary layer (PBL), penetrate into the ASL. The curvature of the vertical profile of mean horizontal alongwind velocity forces the alignment of the convective cells in the flow direction (Kuettner, 1971), which have an average length of several hundreds of metres and an average width of a few tens of metres. This mechanism leads to the formation of turbulent structures, which extend throughout the depth of the ASL. 相似文献
17.
Large-scale turbulent motions enhancing horizontal gas spread in an atmospheric boundary layer are simulated in a wind-tunnel
experiment. The large-scale turbulent motions can be generated using an active grid installed at the front of the test section
in the wind tunnel, when appropriate parameters for the angular deflection and the rotation speed are chosen. The power spectra
of vertical velocity fluctuations are unchanged with and without the active grid because they are strongly affected by the
surface. The power spectra of both streamwise and lateral velocity fluctuations with the active grid increase in the low frequency
region, and are closer to the empirical relations inferred from field observations. The large-scale turbulent motions do not
affect the Reynolds shear stress, but change the balance of the processes involved. The relative contributions of ejections
to sweeps are suppressed by large-scale turbulent motions, indicating that the motions behave as sweep events. The lateral
gas spread is enhanced by the lateral large-scale turbulent motions generated by the active grid. The large-scale motions,
however, do not affect the vertical velocity fluctuations near the surface, resulting in their having a minimal effect on
the vertical gas spread. The peak concentration normalized using the root-mean-squared value of concentration fluctuation
is remarkably constant over most regions of the plume irrespective of the operation of the active grid. 相似文献
18.
北京北郊冬季大风过程湍流通量演变特征的分析研究 总被引：4，自引：0，他引：4
利用中国科学院大气物理研究所325 m气象观测塔1993年12月～1994年1月大气边界层实验资料, 计算分析了大风过境过程中47 m和120 m高度湍流通量演变特征及其影响因子, 以及与风速、 稳定度等参数的关系。结果表明: 大风过程对近地面层的物质能量输送有着重要影响, 大风之前出现短时间动量上传和热量下传; 大风过程中的湍流通量数值明显高于过境后, 水平方向湍流通量数值和能量增加幅度大于垂直方向; 当风速大于临界值5 m/s时, 湍流通量与风速、 湍流动能的相关迅速增大; 湍流谱特征表现为湍流能量的低频部分增加、 湍流谱曲线变宽; 大风能强烈影响近地面层的能量收支。 相似文献
19.
We investigated the ‘local’ and ‘global’ similarity of vertical turbulent transfer of heat, water vapour, and CO2 within an urban surface layer. The results were derived from field measurements in a residential area of Tokyo, Japan during midday on fair-weather days in July 2001. In this study, correlation coefficients and quadrant analysis were used for the evaluation of ‘global’ similarity and wavelet analysis was employed for investigating ‘local’ similarity. The correlation coefficients indicated that the transfer efficiencies of water vapour and CO2 were generally smaller than that of heat. Using wavelet analysis, we found that heat is always efficiently transferred by thermal and organized motions. In contrast, water vapour and CO2, which are passive quantities, were not transferred as efficiently as heat. The quadrant analyses showed that the heat transfer by ejection exceeded that by sweep, and the ratios of ejection to sweep for water vapour and CO2 transfer were less than that for heat. This indicated that heat is more efficiently transferred by upward motions and supported the findings from wavelet analysis. The differences of turbulent transfer between heat and both CO2 and water vapour were probably caused both by the active role of temperature and the heterogeneity in the source distribution of scalars 相似文献
20.
Albert F. Kurbatskiy Lyudmila I. Kurbatskaya 《Meteorology and Atmospheric Physics》2009,104(1-2):63-81
A modified three-parameter model of turbulence for a thermally stratified atmospheric boundary layer (ABL) is presented. The model is based on tensor-invariant parameterizations for the pressure–strain and pressure–temperature correlations that are more complete than the parameterizations used in the Mellor–Yamada model of level 3.0. The turbulent momentum and heat fluxes are calculated with explicit algebraic models obtained with the aid of symbol algebra from the transport equations for momentum and heat fluxes in the approximation of weakly equilibrium turbulence. The turbulent transport of heat and momentum fluxes is assumed to be negligibly small in this approximation. The three-parameter $E - \varepsilon - {\left\langle {\theta ^{2} } \right\rangle }$ model of thermally stratified turbulence is employed to obtain closed-form algebraic expressions for the fluxes. A computational test of a 24-h ABL evolution is implemented for an idealized two-dimensional region. Comparison of the computed results with the available observational data and other numerical models shows that the proposed model is able to reproduce both the most important structural features of the turbulence in an urban canopy layer near the urbanized ABL surface and the effect of urban roughness on a global structure of the fields of wind and temperature over a city. The results of the computational test for the new model indicate that the motion of air in the urban canopy layer is strongly influenced by mechanical factors (buildings) and thermal stratification. 相似文献