共查询到20条相似文献，搜索用时 15 毫秒
1.
An observational analysis of the structures and characteristics of a windy atmospheric boundary layer during a cold air outbreak in the South China Sea region is reported in this paper. It is found that the main structures and characteristics are the same as during strong wind episodes with cold air outbreaks on land. The high frequency turbulent fluctuations(period<1 min) are nearly random and isotropic with weak coherency, but the gusty wind disturbances(1 min相似文献
2.
T. Maitani 《Boundary-Layer Meteorology》1989,48(1-2):19-31
Observations of wind velocity and air temperature fluctuations were made in the nocturnal surface inversion layer over a sorghum field. Wave-like fluctuations of temperature and wind velocity with a period of 15–20 min were observed for about 2 hours, 3 to 5 hours before sunrise. Wave-like fluctuations of temperature were observed in the air layer above and within a plant canopy and were most noticeable at the top of the plant canopy. Spectral analysis of temperature and wind velocity fluctuations reveals a separation of energy into wave-like and turbulent fluctuations. Cospectral analysis shows that for both momentum and heat, vertical transports are partitioned almost equally in the frequency ranges characteristic of wave-like and turbulent fluctuations. This suggests wave- turbulence interactions at low frequencies in the air layer near a plant canopy. 相似文献
3.
《大气和海洋科学快报》2016,(1)
Statistical analysis of turbulent and gusty characteristics in the atmospheric boundary layer under weak wind period has been carried out.The data used in the analysis were from the multilevel ultrasonic anemometer-thermometers at 47 m,120 m,and 280 m levels on Beijing 325 m meteorological tower.The time series of 3D atmospheric velocity were analyzed by using conventional Fourier spectral analysis and decompose into three parts:basic mean flow(period 10 min),gusty disturbances(1 min period 10 min)and turbulence fluctuations(period 1 min).The results show that under weak mean wind condition:1)the gusty disturbances are the most strong fluctuations,contribute about 60% kinetic energy of eddy kinetic energy and 80% downward flux of momentum,although both the eddy kinetic energy and momentum transport are small in comparison with those in strong mean wind condition;2)the gusty wind disturbances are anisotropic;3)the gusty wind disturbances have obviously coherent structure,and their horizontal and vertical component are negatively correlated and make downward transport of momentum more effectively;4)the friction velocities related to turbulence and gusty wind are approximately constant with height in the surface layer. 相似文献
4.
大气边界层强风的阵性和相干结构 总被引：14，自引：5，他引：9
我国北方春季冷锋过境后,常骤发强风,甚至起沙扬尘,持续数小时甚至一二天,通过对边界层超声风温仪的资料分析,可知大风常叠加有周期为3～6 min的阵风,较有规律,且有明显的相干结构:阵风风速峰期有下沉运动,谷期有上升运动;阵风扰动以沿平均流的顺风方向分量为主,横向和垂直方向的分量都较小,其本质是低频次声波和重力波的混合;阵风沿顺风向且向下传播.周期小于1 min的脉动在水平面上基本是各向同性的不规则的湍涡.大风期间,无论是平均流、阵风和湍流脉动,至少在120 m高度以下,主要都有西风和北风动量下传,感热上传.平均流的动量下传强于由脉动下传的量,与一般天气情况不同,而且阵风与湍流的动量下传的量值差不多.平均流和阵风在动量传送上起相当大的作用. 相似文献
5.
The horizontal and vertical wind velocity fluctuations were measured using two sonic anemometers at a height of 135 cm above
a snow surface under a transverse snow wave-forming condition. A snow-wave was formed when the wind at a height of 1 m blew
at a speed of more than 7 m s−1 after an approximate accumulation of from 10 to 20 cm of new snow on a snowfield. For example, when a snow-wave had a wavelength
of 10 m and a wave height of 15 to 20 cm, the measured horizontal and vertical velocity components showed that they had a
frequency peak of 0.7 Hz in coherence and co-spectrum corresponding to this wavelength. The results suggest that wind turbulence
and snow-wave formation interact with each other. 相似文献
6.
The horizontal and vertical wind velocity fluctuations were measured using two sonic anemometers at a height of 135 cm above a snow surface under a transverse snow wave-forming condition. A snow-wave was formed when the wind at a height of 1 m blew at a speed of more than 7 m s–1 after an approximate accumulation of from 10 to 20 cm of new snow on a snowfield. For example, when a snow-wave had a wavelength of 10 m and a wave height of 15 to 20 cm, the measured horizontal and vertical velocity components showed that they had a frequency peak of 0.7 Hz in coherence and co-spectrum corresponding to this wavelength. The results suggest that wind turbulence and snow-wave formation interact with each other. 相似文献
7.
针对2016年湖北梅雨期3次(“6·19”、“7·5”和“7·19”)暴雨过程,首先对比了汉口站探空数据与汉口、咸宁两个风廓线雷达站水平风速、风向,发现“6·19”和“7·5”过程汉口风廓线雷达站3 km以下水平风速和探空数据较为接近,而3次过程中咸宁风廓线雷达站8 km以下水平风向、风速和汉口站探空数据基本吻合。在此基础上利用风廓线雷达资料并结合常规、加密自动气象站资料,对3次过程中水平风场、平均垂直速度及其变率、水平风速垂直切变、大气折射率结构常数(C_(n)^(2))等进行分析。结果表明:(1)降水开始前西南风速明显增大,中层干冷空气入侵和地面冷池形成的中尺度偏东气流是“6·19”过程50站出现大于等于17.2 m·s^(-1)大风的主要原因,“7·5”和“7·19”过程西南急流长时间维持及1 km以下的偏东气流则是短时强降水持续时间较长的诱因;(2)梅雨期暴雨期间风廓线雷达观测的水平风速垂直切变、平均垂直速度及其变率随高度变化较小,较强上升运动区域主要集中在4 km高度以下;(3)C_(n)^(2)显示强降水发生前大气水汽含量有一增加过程,且整层水汽含量深厚,C_(n)^(2)大值区的消失对应降水结束。 相似文献
8.
将2012年5月21日-8月16日广东省湛江市东海岛气象观测站内脉冲激光风廓线仪WINDCUBE V2与气象站内的100 m测风塔进行同步观测试验,在经过观测数据同步性调整、有效性检验和代表性样本筛选基础上,分大小风和有无降雨天气过程,对杯式测风仪、超声风速仪与激光风廓线仪的同步测风数据进行比较,结果显示:脉冲激光风廓线仪与杯式测风仪测量水平风参数的相关性较好,10 min平均风速、风向的线性拟合度均大于0.99,3 s阵风风速的拟合度大于0.96,湍流强度的拟合度大于0.67,风速标准差的拟合度大于0.79;大风情况下,激光风廓线仪对风参数的测量效果更佳。无降雨情况下,激光风廓线仪的测量效果较降雨时略好,10 min降水量小于15 mm的降雨对这款激光风廓线仪的风速、风向、湍流强度、3 s阵风风速的测量没有显著影响,对风速标准差有一定影响。当水平风速增大和有降雨时,激光风廓线仪对垂直速度的测量效果欠佳。该对比分析可为激光风廓线仪观测数据的可靠性提供参考。 相似文献
9.
利用2008-2014年CFL20G风廓线雷达数据对科尔沁草原高空风场垂直特征及变化进行研究。主要对高空三维风场季节变化的统计学特征、典型高度层上的变化规律及垂直高度上的日变化规律进行分析。分析发现：四季中高空20-40m/s风速出现的频率最大,3000米至18000米科尔沁草原高空以偏西风为主。垂直高度上水平风速呈一波一谷型变化,随着高度的增加,高层水平风速开始增大的时间有所推后。12600米及以下各层平均风速最小的季节为夏季,最大的季节为冬春两季；19000米平均风速最小的月份为12月份,风速最大月份为8月份。垂直速度在5500米以下有明显日变化,1500米和3000米有较为明显的年变化,最大值出现在春夏交接的4-6月份,最小值出现在12月份,5000米以上垂直速度没有明显的年变化。 相似文献
10.
M. W. Rotach 《Boundary-Layer Meteorology》1993,66(1-2):75-92
11.
“黄蜂”边界层风速分析——
台风平均风速的时距选取与强度估计 总被引：1，自引：0，他引：1
通过对热带风暴(TC)"黄蜂"登陆的一次边界层观测所得到风速资料的分析计算,取得不同时距下平均风速序列.比较不同时距选取时登陆TC的平均风速、风向和台风强度,发现1 min平均比10 min平均水平最大风速大25.30%,风向变化不大,TC强度指数1 min与10 min相差2%～4%.时距选取较小时,TC平均风速和强度变大,所测得风速区域也变大,而风向与时距的选取没有明显关系.只是在阵风变化比较大的情况下选取小的时距可以更好的表示这种特征.所以时距选取需要对所研究问题的需要进行分析,对不同的问题选取不同的时距以得到更好的结果. 相似文献
12.
双多普勒雷达反演强风暴三维风场的数值试验 总被引：17，自引：4，他引：17
两部雷达测得的径向速度再加上质量连续方程可以求解大气风场，利用这一原理，以1996年6月29日发生在北京东北部京冀交界处的一次强风暴过程为例，用模式反演出风暴体的三维风场结构，误差分析表明和实况基本一致。利用模式输出的三维风场，先模拟两部多普勒雷达扫描的数据，在此基础上，进行三维风场反演，结果表明，反演得到的流场和模拟的流场总体趋势完全一致，风暴的中心位置吻合较好，上升气流和下沉气流的分布也很接近，水平速度分量反演的误差很小，基本上可以反映三维风场的真实情况。垂直速度的平均离差在各个高度上都较小，反演结果较好。 相似文献
13.
Taiichi Hayashi 《Boundary-Layer Meteorology》1992,58(1-2):33-49
The intermittent structure of the turbulent wind field in the atmospheric surface layer is investigated by conditional sampling methods. The results show that downward momentum can be transported efficiently during a peak gust. The horizontal structure of the gust is also revealed by observing the spatial structure of wind speed fluctuations from a network of 28 anemometers. The high wind region consists of a gust front with a sudden increase of wind speed at the front and a slow decrease to its rear. The development of the gust front is related closely to the momentum flux during the short time of passage of the gust. 相似文献
14.
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
15.
G. C. Efthimiou D. Hertwig S. Andronopoulos J. G. Bartzis O. Coceal 《Boundary-Layer Meteorology》2017,163(2):179-201
Wind fields in the atmospheric surface layer (ASL) are highly three-dimensional and characterized by strong spatial and temporal variability. For various applications such as wind-comfort assessments and structural design, an understanding of potentially hazardous wind extremes is important. Statistical models are designed to facilitate conclusions about the occurrence probability of wind speeds based on the knowledge of low-order flow statistics. Being particularly interested in the upper tail regions we show that the statistical behaviour of near-surface wind speeds is adequately represented by the Beta distribution. By using the properties of the Beta probability density function in combination with a model for estimating extreme values based on readily available turbulence statistics, it is demonstrated that this novel modelling approach reliably predicts the upper margins of encountered wind speeds. The model’s basic parameter is derived from three substantially different calibrating datasets of flow in the ASL originating from boundary-layer wind-tunnel measurements and direct numerical simulation. Evaluating the model based on independent field observations of near-surface wind speeds shows a high level of agreement between the statistically modelled horizontal wind speeds and measurements. The results show that, based on knowledge of only a few simple flow statistics (mean wind speed, wind-speed fluctuations and integral time scales), the occurrence probability of velocity magnitudes at arbitrary flow locations in the ASL can be estimated with a high degree of confidence. 相似文献
16.
T. Maitani 《Boundary-Layer Meteorology》1977,12(4):405-423
Turbulent kinetic energy and its vertical flux were measured at two heights over a paddy field. The vertical transport of turbulent kinetic energy was always downward right above the paddy field and was frequently downward at higher levels within a few metres above the crop. Contributions to the downward transport arise mainly from the turbulent kinetic energy of horizontal wind velocity components. It is shown from the analysis of probability distributions that appreciable transport takes place intermittently in a few large downward bursts and that these downdrafts are efficient for downward energy transport.In the budget of turbulent kinetic energy, the flux divergence term and the energy dissipation term are the main loss terms under unstable conditions. These terms increase in magnitude with increasing instability. Buoyant production is insufficient to balance these losses. The imbalance term involving the pressure-work term is probably one of the main energy sources in unstable conditions. 相似文献
17.
Eiji Ohtaki 《Boundary-Layer Meteorology》1980,19(3):315-336
Turbulent fluctuations in CO2 concentrations over a paddy field are measured by a fastresponse device with an open sensing path. This IR device coupled with a sonic anemometer constitutes an eddy correlation instrument to measure CO2 fluxes. Three experiments were conducted in the surface layer over paddy 90 cm high. The stability (z – d)/L ranged from -0.14 to 0.20, where L denotes the Monin-Obukhov length.CO2 power spectra show the range of applicability of the -2/3 power law to be between f = 0.2 and f = 2, where f is the frequency normalized by wind speed and height. The cospectral estimate between CO2 and vertical component of wind speed ranging from f = 0.005 to f = 2 shows a peak at about f = 0.15 under near-neutral stratification.Hourly means of CO2 flux measured by the eddy correlation method increase with intensity of net radiation. The maximum value of downward flux of CO2 rises to 0.6 mg cm-2 hr-1 over the paddy field at the stage of ear emergence.Some turbulence statistics relating to the CO2 transport are evaluated: the correlation coefficient between CO2 and vertical velocity is about -0.3, and that between CO2 and humidity attains -0.7 ~ -0.8 under unstable stratification; nondimensional gradients c for CO2 and m for wind speed are 0.89 and 0.99, respectively. 相似文献
18.
David P. Chock 《Boundary-Layer Meteorology》1980,18(4):431-451
The mean wind field and the wind fluctuations observed near a controlled, heavily traveled level roadway were investigated. The mean wind field was studied in terms of velocity defects relative to the ambient mean wind. The wind fluctuations were studied in terms of energy spectra, velocity cross-spectra, excesses of velocity variances and cross-covariances over their ambient values. Two-point cross-spectra and correlations were also used to study the propagation of wind fluctuations. The influence of traffic on the ambient wind field extended vertically up to at least 4.5m above ground, and horizontally to at least 30 m downwind of the road. The vertical extension was more gradual at high cross-road winds than at low cross-road winds. The wind tended to move up as it approached the road and down as it left the road, except when the cross-road wind was low, where the downward motion was reduced or reversed. This is likely due to the buoyancy effect of the heated exhaust. The traffic effects propagated outward at about 1 m s-1. Thus at cross-road winds of less than 1 ms-1, the influence of traffic could be observed upwind of the road. When intense shear existed between the local wind field and an opposing traffic direction, large turbulent energy production resulted, generating large eddies, in additions to the high frequency (> 0.1 Hz) eddies generated by vehicular motions in the absence of intense shear. The large eddies also increased the mixing volume, so that when the ambient wind opposed the traffic direction on the upwind lanes, the pollutant concentration upwind of the road could be higher than that downwind. While the cross-covariance excesses generally agreed with the gradient transport assumption, disagreements also existed, which may not be surprising in view of the participation of large eddies in the momentum transport. 相似文献
19.
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