共查询到20条相似文献，搜索用时 46 毫秒
1.
The Hilbert–Huang transform (HHT) is applied to analyzing the turbulent time series obtained within the atmospheric boundary layer over the ocean. A method based on the HHT is introduced to reduce the influence of non-turbulent motions on the eddy-covariance based flux by removing non-turbulent modes from the time series. The scale dependence of the flux is examined and a gap mode is identified to distinguish between turbulent modes and non-turbulent modes. To examine the effectiveness of this method it is compared with three conventional methods (block average, moving-window average, and multi-resolution decomposition). The data used are from three sonic anemometers installed on a moored buoy at about 6, 4 and 2.7 m height above the sea surface. For each method, along-wind and cross-wind momentum fluxes and sensible heat fluxes at the three heights are calculated. According to the assumption of a constant-flux layer, there should be no significant difference between the fluxes at the three heights. The results show that the fluxes calculated using HHT exhibit a smaller difference and higher correlation than the other methods. These results support the successful application of HHT to the estimation of air-sea turbulent fluxes. 相似文献
2.
Ultrasonic wind measurements, sonic temperature and air temperature data at two heights in the advection experiment MORE II
were used to establish a complete budget of sensible heat including vertical advection, horizontal advection and horizontal
turbulent flux divergence. MORE II took place at the long-term Carbo-Europe IP site in Tharandt, Germany. During the growing
period of 2003 three additional towers were established to measure all relevant parameters for an estimation of advective
fluxes, primarily of CO2. Additionally, in relation to other advection experiments, a calculation of the horizontal turbulent flux divergence is proposed
and the relation of this flux to atmospheric stability and friction velocity is discussed. In order to obtain a complete budget,
different scaling heights for horizontal advection and horizontal turbulent flux divergence are tested. It is shown that neglecting
advective fluxes may lead to incorrect results. If advective fluxes are taken into account, the sensible heat budget based
upon vertical turbulent flux and storage change only, is reduced by approximately 30%. Additional consideration of horizontal
turbulent flux divergence would in turn add 5–10% to this sum (i.e., the sum of vertical turbulent flux plus storage change
plus horizontal and vertical advection). In comparison with available energy horizontal advection is important at night whilst
horizontal turbulent flux divergence is rather insignificant. Obviously, advective fluxes typically improve poor nighttime
energy budget closure and might change ecosystem respiration fluxes considerably. 相似文献
3.
准确估计水热通量对于认识和理解地气交换与水循环变化过程具有重要意义。利用Penman-Monteith（P-M）模型计算季节尺度水热通量变化的不确定性很大程度上依赖于与冠层变化相关的最小冠层阻力参数,但模型中通常将其设为定值。为此,本文基于多年通量观测采用分段与整体相结合的迭代算法拟合出最小冠层阻力的季节分布。以湖南省宁乡通量观测站为例,针对2012~2015年观测拟合计算最小冠层阻力的季节分布曲线,并利用2016年通量数据进行独立数据验证。结果表明:最小冠层阻力曲线具有鲜明夏低冬高的季节变化特征;利用拟合的具有季节分布的最小冠层阻力改进潜热通量计算,独立数据验证表明其该方法的合理性;相比于原阻力方案得出的潜热模拟结果,其在相关系数、均方根误差和一致性指数都有改进;此外,将该估计方法应用于水热通量的数据插补,较常规统计插补方法,其插补稳定性不随连续缺失数据的增加而降低,而且还能通过模型的微分误差分析量化由于数据输入带来的插补不确定性,在保持通量数据完整性的同时也为数据应用场景提供科学依据。 相似文献
4.
Nan GE Lei ZHONG Yaoming MA Yunfei FU Mijun ZOU Meilin CHENG Xian WANG Ziyu HUANG 《大气科学进展》2021,38(8):1299-1314
正Nan GE1, Lei ZHONG*1,2,3, Yaoming MA4,5,6, Yunfei FU1, Mijun ZOU1,Meilin CHENG1, Xian WANG1, and Ziyu HUANG1 相似文献
5.
Boris Galperin 《Boundary-Layer Meteorology》1986,37(3):245-262
A simple model for turbulent diffusion is proposed based on a turbulent energy model modified by Galperin and Hassid (1986) wherein local equilibrium in the concentration flux equation is assumed resulting in a turbulent diffusivity tensor. The early stage of plume development is simulated through adjustment of the integral length scale of diffusion. A simple semi-empirical formulation is also proposed for the dissipation length scale of concentration variance. Although it is substantially simpler than that of Sykes et al. (1984), the model is shown to compare well with the measurements of Fackrell and Robins (1982a, b). 相似文献
6.
Surface turbulent flux measurements over the Loess Plateau for a semi-arid climate change study 总被引：2，自引：0，他引：2
In order to provide high quality data for climate change studies, the data quality of turbulent flux measurements at the station
of SACOL (Semi-Arid Climate & Environment Observatory of Lanzhou University), which is located on a semi-arid grassland over
the Loess Plateau in China, has been analyzed in detail. The effects of different procedures of the flux corrections on CO2, momentum, and latent and sensible heat fluxes were assessed. The result showed that coordinate rotation has a great influence
on the momentum flux but little on scalar fluxes. For coordinate rotation using the planar fit method, different regression
planes should be determined for different wind direction sectors due to the heterogeneous nature of the ground surface. Sonic
temperature correction decreased the sensible heat flux by about 9%, while WPL correction (correction for density fluctuations)
increased the latent heat flux by about 10%. WPL correction is also particularly important for CO2 fluxes. Other procedures of flux corrections, such as the time delay correction and frequency response correction, do not
significantly influence the turbulent fluxes. Furthermore, quality tests on stationarity and turbulence development conditions
were discussed. Parameterizations of integral turbulent characteristics (ITC) were tested and a specific parameterization
scheme was provided for SACOL. The ITC test on turbulence development conditions was suggested to be applied only for the
vertical velocity. The combined results of the quality tests showed that about 62%–65% of the total data were of high quality
for the latent heat flux and CO2 flux, and as much as about 76% for the sensible heat flux. For the momentum flux, however, only about 35% of the data were
of high quality. 相似文献
7.
8.
Otávio C. Acevedo Osvaldo L. L. Moraes Gervásio A. Degrazia Luiz E. Medeiros 《Boundary-Layer Meteorology》2006,119(1):41-55
The determination of nocturnal surface fluxes in low wind conditions is a major problem for micrometeorological studies. The
eddy correlation technique, extensively used in field measurements, becomes inappropriate if not enough turbulent activity
exists. At the same time, the phenomenon of turbulence intermittency is responsible for the existence of localized events
of short duration within which a large fraction of the total nighttime scalar exchange occurs. The scalar flux within a certain
intermittent event varies considerably depending on the window used for the flux calculation. In many cases, events with very
different time durations occur in the same night, and therefore, the proper determination of the surface flux would require
averaging within data windows of different sizes for each event. In this work, the surface exchanges of temperature, moisture
and carbon dioxide are analysed at a micrometeorological tower at southern Brazil. Intermittent turbulence is a common occurrence
at the location. The analysis shows that the fluxes vary with turbulence intensity and the estimation technique. A variable-window
size method for flux estimation is suggested and shown to cause an increase in the magnitude of the nocturnal surface fluxes 相似文献
9.
Luís Gustavo N. Martins Scott D. Miller Otávio C. Acevedo 《Boundary-Layer Meteorology》2017,163(1):123-141
A methodology based on Empirical mode decomposition (EMD) was used to filter out non-turbulent motions from measurements of atmospheric turbulence over the sea, aimed at reducing their contribution to eddy-covariance (EC) estimates of turbulent fluxes. The proposed methodology has two main objectives: (1) to provide more robust estimates of the fluxes of momentum, heat and CO\(_2\); and (2) to reduce the number of flux intervals rejected due to non-stationarity criteria when using traditional EC data processing techniques. The method was applied to measurements from a 28-day cruise (HALOCAST 2010) in the Eastern Pacific region. Empirical mode decomposition was applied to 4-h long time series data and used to determine the cospectral gap time scale, \(T_\mathrm{{gap}}\). Intrinsic modes of oscillation with characteristic periods longer than the gap scale due to non-turbulent motions were assumed and filtered out. Turbulent fluxes were then calculated for sub-intervals of length \(T_\mathrm{{gap}}\) from the filtered 4-h time series. In the HALOCAST data, the gap scale was successfully identified in 89% of the 4-h periods and had a mean of 37 s. The EMD approach resulted in the rejection of 11% of the flux intervals, which was much less than the 68% rejected when using standard filtering methods based on data non-stationarity. For momentum and sensible heat fluxes, the averaged difference in flux magnitude between the traditional and EMD approaches was small (3 and 1%, respectively). For the CO\(_2\) flux, the magnitude of EMD flux estimates was on average 16% less than fluxes estimated from linear detrended 10-min time series. These results provide evidence that the EMD method can be used to reduce the effects of non-turbulent correlations from flux estimates. 相似文献
10.
Thomas Foken 《Boundary-Layer Meteorology》2006,119(3):431-447
In weak wind stable conditions, eddy-correlation fluxes calculated using conventional averaging times of 5 min or longer to define the perturbations are severely contaminated by poorly sampled mesoscale motions. A method is developed to identify the averaging time for each individual data record that captures the turbulence while excluding most of the mesoscale motions. The method is based on multiresolution decomposition of the heat flux, and provides an objective procedure for selecting the averaging time for calculating eddy-correlation fluxes. Eddy-correlation data collected in weak turbulence conditions over grass, snow, a pine forest and the ocean are used to demonstrate the approach.When the small-scale turbulence and mesoscale motions are clearly separated by a gap region in the heat flux cospectra, the variable window width reduces the influence of nonstationarity by more effectively filtering out mesoscale motions compared to traditional methods using constant averaging time. For records where turbulence and mesoscale motions overlap in scale, the method is not well posed, although such records occur infrequently for our datasets. These ambiguous cases correspond to significant nonstationarity at scales that overlap with turbulence scales. The improved turbulence fluxes calculated with the proposed method are the appropriate fluxes for evaluating flux-gradient relationships and Monin–Obukov similarity theory for developing improved model parameterizations of turbulence for weakly turbulent flows 相似文献
11.
Two situations observed during the second Aerosol Characterization Experiment (ACE-2) are analysed from aircraft measurements in the broken stratocumulus (Sc)-topped marine boundary layer. The first one (26 June 1997), characterized by a non-polluted, oceanic air mass, presents a decoupling between the Sc layer (1400–1520 m) and the turbulent mixed layer, this latter extending from the surface up to 580 m. In contrast, the second case (9 July 1997), during which continental air had been advected over the experimental area, presents a well-coupled layer extending from the surface up to the top of the Sc layer(910 m). This coupling, uncommon in this area in the middle of the day, isrelated to the relative shallowness of the boundary layer. For both situations,it is shown that the turbulent fluxes can be computed with reasonably goodaccuracy (better than 10 %), taking into account both the random and thesystematic errors involved in the eddy-correlation technique. Estimationof random error is based on the computation of the integral scale of thecovariance, and systematic error is estimated from the parameterizationof Mann and Lenschow. The fluxes show that the buoyancy, as a sourceof turbulence, is due to latent heat flux rather than sensible heat flux,with values comparable to previous experiments in the Azores-Canariesbasin. In addition, we propose a method to analyse, for coupled situations,the relationship between the fractional cloudiness and the organization ofthe turbulent field below the clouds. This method is based on a conditionalsampling technique. It is shown that this organization cannot be deducedfrom the analysis of the velocity signal, which is dominated by turbulence.However, when the signals are conditionally sampled according to thepresence or absence of clouds, a weak cloud-related organization can beshown, and the cloud-related transports quantified; the values found areof the order of 10 % of the total transfers, i.e. the same order of magnitude asthe errors on the total flux computation. The method developed is thereforepromising, provided that the uncertainties can be reduced by analyzing a highamount of data. 相似文献
12.
The spectral structure of turbulence (spectra and cospectra) and water content characteristics for convective clouds in the tropical region was analyzed using aircraft observations in the meteorological testbed over Cuba; the results are presented. The cospectra for vertical turbulent heat fluxes allow classifying convective clouds based on their development stage and revealing the stages of growth, stabilization, and dissipation of clouds. It is shown that the value of cloud air overheating as compared to the ambient space is a parameter defining the cloud development stage. The interrelation is revealed between the integral characteristics of turbulence and water content (the mean values and distribution functions of parameters) for different stages of development of convective clouds. The recommendations are formulated on using the data on the dynamic structure of clouds for weather modification activities. A method is proposed for the instrumental estimation of cloud suitability for seeding that is aimed at precipitation augmentation. 相似文献
13.
The effectiveness of closure assumptions implemented in turbulent boundary-layer models is rather uncertain over complex terrain. Different closure schemes for Reynolds shear stress based on the mixing-length concept are compared with data from wind tunnel experiments over complex terrain and the results are analysed on the basis of second-order moment equations. A good estimation of the vertical momentum flux velocity scale turns out to be given by the standard deviation of the vertical velocity while the turbulent kinetic energy scaling gives less satisfactory results in regions where turbulence anisotropy is large. Fairly good results are given by closure models implementing a shear-limited mixing-length already proposed for non-logarithmic wind profiles, while large errors characterize traditional mixing-length formulations. 相似文献
14.
基于矩阵补全的气象数据推测 总被引：1，自引：0，他引：1
传统的气象数据推测大多基于插值方法,而此方法需要近邻台站的完整观测数据,这在很大程度上限制了插值方法的应用。为此,本文提出了一种基于矩阵补全的气象数据推测方法,该方法根据气象数据的近似低秩性来推测缺失数据。首先,选取我国662个气象台站2004—2013年的逐日平均温度和日照时数两种气象要素作为研究对象,通过矩阵奇异值的累积贡献率来检验数据集的近似低秩性。然后设计了两组试验,第1组试验考虑了不同采样概率下各年份的数据推测,第2组试验随机选取某些台站,考虑所选台站数据连续缺测时的推测。最后,使用矩阵补全方法推测缺失数据,采用10a的平均误差作为评价指标。试验结果表明:矩阵补全方法能很好地推测缺失数据,且具有一定的鲁棒性。 相似文献
15.
Adaptation of the optimal fingerprint method for climate change detection using a well-conditioned covariance matrix estimate 总被引：3，自引：3，他引：0
The “optimal fingerprint” method, usually used for detection and attribution studies, requires to know, or, in practice, to
estimate the covariance matrix of the internal climate variability. In this work, a new adaptation of the “optimal fingerprints”
method is presented. The main goal is to allow the use of a covariance matrix estimate based on an observation dataset in
which the number of years used for covariance estimation is close to the number of observed time series. Our adaptation is
based on the use of a regularized estimate of the covariance matrix, that is well-conditioned, and asymptotically more precise,
in the sense of the mean square error. This method is shown to be more powerful than the basic “guess pattern fingerprint”,
and than the classical use of a pseudo-inverted truncation of the empirical covariance matrix. The construction of the detection
test is achieved by using a bootstrap technique particularly well-suited to estimate the internal climate variability in real
world observations. In order to validate the efficiency of the detection algorithm with climate data, the methodology presented
here is first applied with pseudo-observations derived from transient regional climate change scenarios covering the 1960–2099
period. It is then used to perform a formal detection study of climate change over France, analyzing homogenized observed
temperature series from 1900 to 2006. In this case, the estimation of the covariance matrix is only based on a part of the
observation dataset. This new approach allows the confirmation and extension of previous results regarding the detection of
an anthropogenic climate change signal over the country. 相似文献
16.
选取30多年来近地层湍流通量研究中具有代表性的六种参数化方案, 应用GAME/Tibet试验中那曲通量观测站的实测资料, 对比分析了各方案计算所得的湍流动量输送系数 (CM) 之间的差异。结果表明:六种参数化方案计算得到的湍流动量输送系数之间存在较大差异。对于那曲观测站稀疏短草下垫面而言, 稳定条件下当理查孙数小于0.1时, 除Businger71方案存在显著低估以外, 其他各方案均能较好估算湍流动量输送系数; 不稳定条件下, Dyer74方案对湍流动量输送系数的估算效果最好, 其次为Wang02, Launiainen95和Louis82方案, Businger71方案误差较大。 相似文献
17.
Nelson Luís Dias Bianca Luhm Crivellaro Marcelo Chamecki 《Boundary-Layer Meteorology》2018,168(3):387-416
The Hurst phenomenon is a well-known feature of long-range persistence first observed in hydrological and geophysical time series by E. Hurst in the 1950s. It has also been found in several cases in turbulence time series measured in the wind tunnel, the atmosphere, and in rivers. Here, we conduct a systematic investigation of the value of the Hurst coefficient H in atmospheric surface-layer data, and its impact on the estimation of random errors. We show that usually \(H > 0.5\), which implies the non-existence (in the statistical sense) of the integral time scale. Since the integral time scale is present in the Lumley–Panofsky equation for the estimation of random errors, this has important practical consequences. We estimated H in two principal ways: (1) with an extension of the recently proposed filtering method to estimate the random error (\(H_p\)), and (2) with the classical rescaled range introduced by Hurst (\(H_R\)). Other estimators were tried but were found less able to capture the statistical behaviour of the large scales of turbulence. Using data from three micrometeorological campaigns we found that both first- and second-order turbulence statistics display the Hurst phenomenon. Usually, \(H_R\) is larger than \(H_p\) for the same dataset, raising the question that one, or even both, of these estimators, may be biased. For the relative error, we found that the errors estimated with the approach adopted by us, that we call the relaxed filtering method, and that takes into account the occurrence of the Hurst phenomenon, are larger than both the filtering method and the classical Lumley–Panofsky estimates. Finally, we found that there is no apparent relationship between H and the Obukhov stability parameter. The relative errors, however, do show stability dependence, particularly in the case of the error of the kinematic momentum flux in unstable conditions, and that of the kinematic sensible heat flux in stable conditions. 相似文献
18.
B. A. Kader 《Boundary-Layer Meteorology》1992,61(4):323-347
Methods are studied which permit one to evaluate turbulent fluxes from the results of spectral measurements in turbulent laboratory flows and an unstable atmospheric surface layer. The well known dissipation method of flux measurements, which uses spectral data related to the inertial range, is reanalyzed. New theoretical ideas and the latest experimental data are used to specify this method in cases of moderately and very strongly unstable thermal stratifications.Moreover, it is also explained how to estimate momentum and heat fluxes from data in the low frequency parts of the velocity and temperature spectra in the low frequency ranges beyond the lower limit of the inertial range. This permits one to estimate fluxes using rather simple and cheap instruments (e.g., Pilot-tubes and thermocouples in laboratory flows or cup anemometers and crude resistance thermometers in meteorological studies). The equations for flux determination are based in such cases on the recent models by Kader (1987, 1988) and Kader and Yaglom (1990, 1991) of spectral shapes at mesoscale wave numbers; these models agree quite satisfactorily with many (though not all) data of direct spectral measurements. It is shown that estimated momentum and heat fluxes in the laboratory and in an unstably stratified atmospheric surface layer obtained by the method suggested in this paper agree satisfactorily with direct flux measurements. 相似文献
19.
Important questions concerning the turbulent exchange of atmospheric pollutants between the air and natural surfaces urgently require answers, but sensors for many important species are not yet sufficiently well developed for use with standard micrometeorological methods. There is need, therefore, to develop methods by which deficient sensors can be used in micrometeorological applications. There is also need to extend micrometeorological methods to circumstances which do not satisfy the conventional perfect-site constraints. Here, methods based upon the assumption of cospectral similarity are explored. Initial tests indicate that it is possible to estimate daytime turbulent fluxes with sensors giving response times considerably greater than the values normally quoted for eddy correlation (e.g., 5 s instead of 1 s), and to compute first-order corrections for the error resulting from the lack of detection of high-frequency turbulence. It is suggested that a similar method might be used to derive flux data in terrain more complex than can be handled by conventional micrometeorology. The techniques outlined here should be applied only with caution, but appear adequate to permit the use of deficient sensors in some circumstances, and good sensors over some micrometeorologically deficient terrain. 相似文献
20.