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1.
M. A. Novitskii L. M. Khachaturova L. K. Kulizhnikova M. K. Matskevich 《Russian Meteorology and Hydrology》2007,32(3):168-175
On the basis of wind direction measurements with 1-s discreteness at the meteorological tower VMM-310 in the town of Obninsk, maximum fluctuations of wind direction are obtained with 10-s averaging over limited time intervals that correspond to the transport of pollutant puffs at distances about 10 km from the source at altitudes up to 300 m. Average values of maximum fluctuations of wind direction decrease with increasing wind speed, level of measurements, and stratification stability. Examples are presented of distributions of maximum fluctuations of wind direction as dependent of these factors. Parameters are given of distributions of maximum fluctuations of wind direction at six levels under different wind speeds and different atmospheric stability. The empirical distributions are approximated by Weibull distribution, and parameters of the latter are presented for separate levels. The results obtained can be used for estimation of an angular size of an area of possible pollution under different conditions of atmospheric stratification, wind speed, and levels of transport of an instantaneous puff of pollutants for the pollutant cloud motion up to a distance of 10 km from the source. 相似文献
2.
实际风速脉动普遍具有自相似分形特征,而传统的谐波合成法和线性滤波法仿真的风速脉动均不具有自相似分形特征.因此,基于随机型Weierstrass-Mandelbrot函数,设计了一种能够仿真自相似风速脉动的方案.其中,表征风速脉动自相似特征的重要参数分形维度可与湍流惯性区能谱的幂指数建立联系.将该方案仿真的风速脉动与实际风速脉动一些重要的统计特征,如功率谱和概率密度函数等,进行了比较,结果表明提出的新方案能有效仿真风速脉动的中高频变化及其概率分布特征. 相似文献
3.
Simultaneous temperature fluctuations have been measured along directions both parallel and orthogonal to the wind direction in the atmospheric surface layer. Ensemble-averaged temperature distributions associated with the ramp-like feature observed in instantaneous temperature traces indicate that the average duration of the ramp is approximately independent of height. Application of Davenport's geometric similarity of coherence of temperature fluctuations yields approximate estimates for the spatial extent of the structure characterized by the ramp. The longitudinal extent is approximately 12 times the vertical extent and 17 times the lateral extent. 相似文献
4.
我国粮食产量气象分量的周期波动初探 总被引：1，自引：0，他引：1
本文应用功率谱、周期图和方差分析等方法探讨了全国及部分代表省(区)粮食单产中气象分量的中短周期波动。发现各地气象分量的谱分布基本相似,普遍存在4—6年及其倍数的周期波动。同时,各地表现又略有不同,由南往北周期逐渐变长。通过与农业气象热量因子以及粮食产量增减产年历史演变的周期波动的比较,似可初步推理为,热量因子的周期波动影响了气象产量的周期波动,从而导致作物产量的周期演变。这一初步推理为我国粮食产量的气象预测预报的基础研究和实践应用提供了参考依据。 相似文献
5.
6.
Meteorological parameters, such as temperature, rainfall, pressure, etc., exhibit selfsimilar space–time fractal fluctuations generic to dynamical systems in nature such as fluid flows, spread of forest fires, earthquakes, etc. The power spectra of fractal fluctuations display inverse power-law form signifying long-range correlations. A general systems theory model predicts universal inverse power-law form incorporating the golden mean for the fractal fluctuations. The model predicted distribution was compared with observed distribution of fractal fluctuations of all size scales (small, large and extreme values) in the historic month-wise temperature (maximum and minimum) and total rainfall for the four stations Oxford, Armagh, Durham and Stornoway in the UK region, for data periods ranging from 92 years to 160 years. For each parameter, the two cumulative probability distributions, namely cmax and cmin starting from respectively maximum and minimum data value were used. The results of the study show that (i) temperature distributions (maximum and minimum) follow model predicted distribution except for Stornowy, minimum temperature cmin. (ii) Rainfall distribution for cmin follow model predicted distribution for all the four stations. (iii) Rainfall distribution for cmax follows model predicted distribution for the two stations Armagh and Stornoway. The present study suggests that fractal fluctuations result from the superimposition of eddy continuum fluctuations. 相似文献
7.
Thunder-day occurrences during a 100-year period based on data from carefully screened records of 86 first-order stations distributed across the United States were assessed for temporal fluctuations and trends during 1896–1995. Short-term (<10-year) fluctuations of adjacentstations were often dissimilar reflecting localized differences in storm activity in a few years, making spatial interpretations difficult. But, temporal fluctuations based on 20-year and longer periods exhibited regional coherence reflecting the control of large, synoptic-scale weather systems on the distribution of thunderstorms over broad areas. Classification of station fluctuations based on 20-year periods revealed six types of distributions existed and they formed 12 discrete areas across the nation. One type present in the lower Midwest and the South had a peak in storm activity in 1916–1935 followed by a general decline to 1976–1995.A second type maximizing at the same time had its minimum earlier, in 1956–1975. Another distribution found at stations in the upper Midwest and Northeast had a mid-century peak (1936–1955) with a recent minimum in1976–1995. A fourth distribution also peaked in 1936–1955 but had an early minimumin 1896–1915, and it mainly occurred in the northern plains and Rocky Mountains. A fifth distribution peaked during 1956–1975 and was foundat stations in four areas including the central High Plains, Southwest, northern Great Lakes, and Southeast. The sixth temporal distribution showed a steady increase in storm activity during the 100-year period, peaking in 1976–1995, and covered a large area extending from the Pacific Northwestacross the central Rockies and into the southern High Plains. The national average distribution based on all station values peaked in mid century. The national distribution differs markedly from several regional distributions illustrating the importance of using regional analysis to assess temporal fluctuations in severe weather conditions in the nation. The 100-year linear trends of the 86 stations defined six regions across the U.S. Significant upward trends existed over most of the western two-thirds of the nation, unchanging trends existed in the northern plains and Midwest, and downward trends were found in most of the nation's east. The up trends in storm-day frequencies in the southern plains occurred where storm damage is greatest and where demographic changes have added to storm losses over time. The national patterns of trends and storm distributions were similar to those found for hail. The temporal distributions of storm activity helped explain recent increases in major storms and their losses, conditions which have increased in the west and south. 相似文献
8.
Eugene Yee P. R. Kosteniuk G. M. Chandler C. A. Biltoft J. F. Bowers 《Boundary-Layer Meteorology》1993,65(1-2):69-109
Measurements have been made of concentration fluctuations in a dispersing plume from an elevated point source in the atmospheric surface layer using a recently developed fast-response photoionization detector. This detector, which has a frequency response (–6 dB point) of about 100 Hz, is shown to be capable of resolving the fluctuation variance contributed by the energetic subrange and most of the inertial-convective subrange, with a reduction in the fluctuation variance due to instrument smoothing of the finest scales present in the plume of at most 4%.Concentration time series have been analyzed to obtain the statistical characteristics of both the amplitude and temporal structure of the dispersing plume. We present alongwind and crosswind concentration fluctuation profiles of statistics of amplitude structure such as total and conditional fluctuation intensity, skewness and kurtosis, and of temporal structure such as intermittency factor, burst frequency, and mean burst persistence time. Comparisons of empirical concentration probability distributions with a number of model distributions show that our near-neutral data are best represented by the lognormal distribution at shorter ranges, where both plume meandering and fine-scale in-plume mixing are equally important (turbulent-convective regime), and by the gamma distribution at longer ranges, where internal structure or spottiness is becoming dominant (turbulent-diffusive regime). The gamma distribution provides the best model of the concentration pdf over all downwind fetches for data measured under stable stratification. A physical model is developed to explain the mechanism-induced probabilistic schemes in the alongwind development of a dispersing plume, that lead to the observed probability distributions of concentration. Probability distributions of concentration burst length and burst return period have been extracted and are shown to be modelled well with a powerlaw distribution. Power spectra of concentration fluctuations are presented. These spectra exhibit a significant inertial-convective subrange, with the frequency at the spectral peak decreasing with increasing downwind fetch. The Kolmogorov constant for the inertial-convective subrange has been determined from the measured spectra to be 0.17±0.03. 相似文献
9.
淮河流域秸秆焚烧关键期主要大气污染物浓度时空分布特征 总被引：2，自引：0，他引：2
基于2015年6月淮河流域卫星遥感监测火点信息、环境空气质量监测数据和常规气象观测资料,利用ANUSPLIN和ArcGISKriging方法对气象要素和主要大气污染物浓度空间栅格化,分析了秸秆焚烧关键期内AQI和主要污染物浓度的时空变化特征及其与气温、相对湿度、风速等气象要素的相关关系。结果表明:秸秆焚烧关键期内,淮河流域城市AQI、PM10与PM2.5浓度均明显升高,且与卫星监测火点具有一定时空响应关系。在时间变化上,AQI、PM10与PM2.5浓度6月上中旬呈波动上升,6月下旬趋于回落;在空间分布方面,AQI、PM10与PM2.5浓度三者分布形态相似,总体上呈现"南低北高、两高一低"分布特征;期间AQI、PM10与PM2.5浓度与气温呈显著正相关,与相对湿度呈显著负相关,与风速的相关性不显著。 相似文献
10.
The mean and short-term fluctuations of carbon dioxide concentration, air temperature, and horizontal wind speed were measured simultaneously within and above a maize crop. Although fluctuations were large at each of the 10 measurement heights, the largest were at the 180-cm level, the densest part of the crop. These short-term fluctuations indicated the broad range of environmental conditions to which plants are exposed (and which plants create or modify) in the field. The statistics of the distributions of these meteorological elements are discussed and the deviations from steady-state conditions are examined by determining linear trends. Finally, variance spectra showed the periodicity of the variations of these meteorological elements.Contribution from the Agricultural Research Service, US Department of Agriculture in cooperation with N.Y. State College of Agriculture, Cornell University, Ithaca, No. 1205. CBRI Contribution No. 966. 相似文献
11.
B. M. Koprov S. L. Zubkovsky V. M. Koprov M. I. Fortus T. I. Makarova 《Boundary-Layer Meteorology》1998,88(3):399-423
Surface-layer convection is investigated by analyzing multi-point measurements of temperature and velocity fluctuations at different sets of spatial points.The visual analysis of temperature and velocity fluctuations measured by sensors mounted on a mast of 36-m height clearly reveals the presence of large-scale convective cells (known as ramp structures) making large contributions to the heat transfer from the ground to lower atmosphere. The vertical temperature variability is described with the aid of empirical orthogonal functions derived from temperature covariance matrices for the heights of 1, 2, 5, 10, 18 and 36 m. Temporal-spatial correlation functions obtained allow estimates of a characteristic velocity scale, which may be interpreted as the downwind velocity of ramp structures. 相似文献
12.
利用1984年N1月—1985年2月和1985年5—8月的欧洲中期预报中心格点资料,计算了北半球低频(40—50)天扰动动能和正压动能的分布以及时间平均气流与低频扰动的相互作用.发现高空低频扰动动能的高值区与西风急流的纬向非对称性和经向切变关系密切。在西风急流的出口区,特别是东亚西风急流的出口区,时间平均气流向低频扰动输送动能,这些地区的低频正压性也最强.亚洲季风区低频正压动能较小。提出可以用低频正压动能与低频动能的比值作为低频扰动的“结构参数”,“结构参数”为0.5的等值线可作为区分热带地区低频振荡与中高纬地区低频振荡的特征线. 相似文献
13.
We describe a new high-resolution sampling technique which can be used to measure concentration fluctuations simultaneously at several points in space. The technique has been used to measure the probability distribution function as a function of the detector location relative to a continuous and steady source. Results are compared to previous experiments and theoretical predictions. The spectra of the concentration fluctuations are analyzed and their behaviour as a function of downwind distance from the source is described. 相似文献
14.
The turbulence in a laboratory convective mixed layer is probed more extensively than in the preliminary study of Willis and Deardorff (1974), and results presented. Turbulence intensities, spectra and probability distributions using mixed-layer scaling compare favorably with similarly scaled field measurements not available or plentiful in 1974. However, the velocity spectra in the convection tank exhibit only a short inertial subrange due to the close proximity of the dissipation subrange to the energy-containing range.The turbulence budget suggests that the convergence of the vertical transport of pressure fluctuations is a rather important term.Results on the entrainment rate are also presented, using both mixed-layer scaling and local interfacial scaling. 相似文献
15.
Organized Structure of Active Turbulence Over an Array of Cubes within the Logarithmic Layer of Atmospheric Flow 总被引：2，自引：2，他引：0
We investigate the coherent structure of atmosphere turbulence over very large roughness within a fully rough, high Reynolds number turbulent flow. The horizontal distributions of coherent turbulence were determined by multipoint measurements of velocity fluctuations using sonic anemometers in a comprehensive outdoor scale model experiment for urban climate (COSMO). COSMO is made up of 512 cubical obstacles, each 1.5 m on a side, arranged in a rectangular pattern on a flat 50 m × 100 m concrete plate. A total of 15 sets of sonic anemometers were aligned horizontally within the logarithmic layer above this site. The velocity fluctuations observed in COSMO were decomposed into active and inactive contributions by applying a spatial-filtering method, and which used a simple moving average along the spanwise direction of the predominant flow as a filter function. The size of the filter should be between the sizes of the active and inactive fluctuations. This method potentially eliminates the considerable portion of low frequency modes included in the horizontal velocity fluctuation, while preserving well the Reynolds stress. The structural characteristics of the active turbulence were qualitatively similar to those measured over various surface configurations. Overall, the observed structures of the active turbulence are composed of very large streaks of low momentum fluid elongated in the streamwise direction with some sub-structures included in the streaks. The sub-structures were the main cause of the ejections, which accompany horizontal vortices. The active motion, including the streaky structures, did not reproduce the lower frequency peak of the bi-modal distribution of the horizontal velocity spectra, but reproduced the higher frequency mode that robustly follows inner-layer similarity (i.e. Monin–Obukhov similarity). 相似文献
16.
Probability density distributions of vertical velocity fluctuations from the daytime convective boundary layer and from convection within a nighttime stratocumulus-capped boundary layer are described and contrasted. Some implications for the diffusion of released, neutrally buoyant, material are identified and discussed. 相似文献
17.
Emilie Perraud Fleur Couvreux Sylvie Malardel Christine Lac Valéry Masson Odile Thouron 《Boundary-Layer Meteorology》2011,140(2):263-294
In numerical weather prediction and climate models, planetary boundary-layer (PBL) clouds are linked to subgrid-scale processes
such as shallow convection. A comprehensive statistical analysis of large-eddy simulations (LES), obtained for warm PBL cloud
cases, is carried out in order to characterize the distributions of the horizontal subgrid cloud variability. The production
of subgrid clouds is mainly associated with the variability of the total water content. Nevertheless, in the case of PBL clouds,
the temperature variability cannot be completely discarded and the saturation deficit, which summarizes both temperature and
total water fluctuations, provides a better representation of the cloud variability than the total water content. The probability
density functions (PDFs) of LES saturation deficit generally have the shape of a main asymmetric bell-shaped curve with a
more or less distinct secondary maximum specific to each type of PBL clouds. Unimodal theoretical PDFs, even those with a
flexible skewness, are not sufficient to correctly fit the LES distributions, especially the long tail that appears for cumulus
clouds. They do not provide a unified approach for all cloud types. The cloud fraction and the mean cloud water content, diagnosed
from these unimodal PDFs, are largely underestimated. The use of a double Gaussian distribution allows correction of these
errors on cloud fields and provides a better estimation of the cloud-base and cloud-top heights. Eventually, insights for
the design of a subgrid statistical cloud scheme are provided, in particular a new formulation for the weight of the two Gaussian
distributions and for the standard deviation of the convective distribution. 相似文献
18.
在夜间稳定边界层中, 湍流热通量往往具有间歇性特征。在一阵阵出现的强度较大的湍流热通量之间, 混杂着弱噪声或其他微弱的难以辨识的高频脉动信号。为了研究间歇性湍流热通量的特征, 必须将这些无关信 号剔除, 以提取出干净的湍流热通量。本文提出了一种新的提取间歇性湍流热通量的方法, 该方法通过分析 湍流热通量的概率密度函数, 并与稳定分布进行比较, 湍流热通量的概率密度函数开始偏离稳定分布的位置, 即是间歇性湍流热通量开始出现的阈值。本文通过夜间稳定边界层外场试验数据的验证, 发现利用稳定分布确定 的阈值可有效地提取出间歇性湍流热通量。在此基础之上, 本文对比了提取前后湍流热通量的功率谱, 发现 提取后低频信号的方差所占比重下降, 而高频信号略有上升。此外, 间歇性湍流热通量在高频区的功率谱满足“-7/6”律。 相似文献
19.
Spectral Structure of Small-Scale Turbulent and Mesoscale Fluxes in the Atmospheric Boundary Layer over a Thermally Inhomogeneous Land Surface 总被引：1，自引：0，他引：1
Spectral analysis was performed on aircraft observations of a convective boundary layer (CBL) that developed over a thermally
inhomogeneous, well-marked mesoscale land surface. The observations, part of the GAME-Siberia experiment, were recorded between
April and June 2000 over the Lena River near Yakutsk City. A special integral parameter termed the ‘reduced depth of the CBL’
was used to scale the height of the mixed layer with variable depth. Analysis of wavelet cospectra and spectra facilitated
the separation of fluxes and other variables into small-scale turbulent fluctuations (with scales less than the reduced depth
of the CBL, approximately 2 km) and mesoscale fluctuations (up to 20 km). This separation approach allows for independent
exploration of the scales. Analyses showed that vertical distributions obeyed different laws for small-scale fluxes and mesoscale
fluxes (of sensible heat, water vapour, momentum and carbon dioxide) and for other variables (wind speed and air temperature
fluctuations, coherence and degree of anisotropy). Vertical profiles of small-scale turbulent fluxes showed a strong decay
that differed from generally accepted similarity models for the CBL. Vertical profiles of mesoscale fluxes and other variables
clearly showed sharp inflections at the same relative (with respect to the reduced depth of the CBL) height of approximately
0.55 in the CBL. Conventional similarity models for sensible heat fluxes describe both small-scale turbulent and mesoscale
flows. The present results suggest that mesoscale motions that reach up to the relative level of 0.55 could be initiated by
thermal surface heterogeneity. Entrainment between the upper part of the CBL and the free atmosphere may cause mesoscale motions
in that region of the CBL. 相似文献
20.
J. Juras 《Theoretical and Applied Climatology》1994,49(2):69-76
Summary This paper deals with various transformations commonly employed in order to obtain near normal distributions of precipitation data. In particular, we discuss the properties of the square-root-normal distribution and its relationship to the other commonly used two-parameter distributions. Similarities of different distributions are discussed with the aid of the normal probability graph and the moment-ratio diagram. The latter has the coefficient of variation on the abscissa and the coefficient of skewness on the ordinate. The examination of some historical data sets with the help of these diagrams demonstrates a large variety of forms, but also points to some of their common characteristics.With 3 Figures 相似文献