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1.
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
2.
Ekman动量近似下中间边界层模式中的风场结构 总被引：2，自引：0，他引：2
发展了一个准三维的、中等复杂的边界层动力学模式，该模式包含了EKman动量近似下的惯性加速度和Blackadar的非线性湍流粘性系数，它进一步改进了Tan和Wu(1993）提出的边界层理论模型。该模型在数值计算复杂性上与经典Ekman模式相类似，但由于包含了Ekman动量近似下的惯性项，使得该模式比传统Ekman模式更近于实际过程。中详细地比较了该模式与其他简化边界层模式在动力学上的差异，结果表明：在经典的Ekman模式中，由于忽略了流动的惯性项作用，导致在气旋性切变气流（反气旋性切变气流）中风速和边界层顶部的垂直速度的高估（低估），而在半地转边界层模式中，由于高估了流动惯性项的作用，结果与经典Ekman模式相反。同样，该模式可以应用于斜压边界层，对于Ekman动量下的斜压边界层风场同时具有经典斜压边界层和Ekman动量近似边界层的特征。 相似文献
3.
NUMERICAL ANALYSIS OF THREE-DIMENSIONAL STRUCTURE OF THE SEA BREEZE OVER SOUTHWESTERN BOHAI GULF 总被引：1，自引：0，他引：1 
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下载免费PDF全文 Wu Zengmao 《Acta Meteorologica Sinica》1988,2(2):175-186
In this paper,a simulation study is made on the sea breeze process over southwestern Bohai Gulf byuse of the Pielke mesoscale meteorological model.The simulated results show that when a south wind of 8m/s blows over the top of the model,a strong wind zone of 15—25 km wide with a maximum speed more than14 m/s,which is close and nearly parallel to the south shore,will appear at 160 m above the sea surface.When a strong sea breeze penetrates inland,there often appears a thermal internal boundary layer(TIBL)near shore.The inversion above the TIBL can damp the vertical dispersion of atmospheric pollution.Besides,it is also found that,for a three-dimensional sea/land breeze circulation,if the divergence centre inthe return flow departs vertically far from the correspondent convergence centre in the sea breeze,a centre ofstrong descending movement will be formed at the middle and upper levels of the return flow.The resultsin this paper is also applicable to the Laizhou Bay. 相似文献
4.
Given incident logarithmic profiles of wind and pollutant concentration above a rough, absorbing surface, the three-dimensional distribution of pollutant concentration over a hill of gentle slope is determined from a linearized model. The model is applied in neutrally stratified flow, without chemistry, and is integrated using spectral methods in the horizontal and a finite-difference scheme in the vertical. This approach allows for flexibility in choosing a closure scheme and a variety of surface boundary conditions. This was not possible in the analytic approach of Padro (1987) who added pollutant concentration and flux to the MS3DJH/1 model of Walmsley et al. (1980). The present model requires as input the turbulent kinetic energy, E, dissipation, , and the perturbation vertical velocity, w, from the three-dimensional boundary-layer flow model of Beljaars et al. (1987), hereinafter referred to as MSFD, The latter model also supplies wind velocity perturbations at the upper boundary, as input to upper boundary conditions on the pollutant flux perturbations.The present study describes applications of the model to idealized terrain features: isolated two- and three-dimensional hills and ridges and an infinite series of ridges. (Application to real terrain, however, presents no difficulties.) Comparisons were made with different (though uniform) surface roughnesses. Tests were performed to examine the effect of upstream terrain features in the periodic domain and to illustrate the importance of the vertical resolution of the output for interpreting results from the sinusoidal terrain case. 相似文献
5.
Wind field simulation in the surface layer is often used to manage natural resources in terms of air quality,gene flow(through pollen drift),and plant disease transmission(spore dispersion).Although Lagrangian stochastic(LS)models describe stochastic wind behaviors,such models assume that wind velocities follow Gaussian distributions.However,measured surface-layer wind velocities show a strong skewness and kurtosis.This paper presents an improved model,a non-Gaussian LS model,which incorporates controllable non-Gaussian random variables to simulate the targeted non-Gaussian velocity distribution with more accurate skewness and kurtosis.Wind velocity statistics generated by the non-Gaussian model are evaluated by using the field data from the Cooperative Atmospheric Surface Exchange Study,October 1999 experimental dataset and comparing the data with statistics from the original Gaussian model.Results show that the non-Gaussian model improves the wind trajectory simulation by stably producing precise skewness and kurtosis in simulated wind velocities without sacrificing other features of the traditional Gaussian LS model,such as the accuracy in the mean and variance of simulated velocities.This improvement also leads to better accuracy in friction velocity(i.e.,a coupling of three-dimensional velocities).The model can also accommodate various non-Gaussian wind fields and a wide range of skewness–kurtosis combinations.Moreover,improved skewness and kurtosis in the simulated velocity will result in a significantly different dispersion for wind/particle simulations.Thus,the non-Gaussian model is worth applying to wind field simulation in the surface layer. 相似文献
6.
The structure and evolution of the sea breeze in the north-west part of the Mediterranean (Catalonia, north-east Spain) is
studied both experimentally and, predominantly, using numerical models to increase understanding of sea-breeze structure and
three-dimensional (3D) pollution distributions in coastal environments. Sea-breeze components are modelled and analyzed using
the fifth-generation Pennsylvania State University–National Centre for Atmospheric Research Mesoscale Model (MM5). The results
show that the growth and structure of the sea-breeze circulation is modulated by the synoptic flow and especially by the complex
topography of the area. 3D pollution transport in a sea breeze is modelled by coupling the MM5 to the Community Multiscale
Air Quality (CMAQ) model, with results indicating that topography and synoptic flow are the main factors modulating horizontal
and vertical pollutant transport in sea-breeze episodes. In this way, horizontal dispersion is limited by the complex topography
of the area, whilst the sea-breeze flow is intensified by anabatic upslope winds that contribute to vertical pollutant transport.
The numerical model results also indicate that the sea-breeze circulation with a weak return flow at upper levels grows due
to a synoptic onshore wind component. However, such a sea-breeze circulation is capable of transporting pollutants towards
the coast. 相似文献
7.
ＡＭｏｄｅｌＳｔｕｄｙｏｆＴｈｒｅｅ－ＤｉｍｅｎｓｉｏｎａｌＷｉｎｄＦｉｅｌｄＡｎａｌｙｓｉｓｆｒｏｍＤｕａｌ－ＤｏｐｐｌｅｒＲａｄａｒＤａｔａＫｏｎｇＦａｎｙｏｕ（孔凡铀）；ＭａｏＪｉｅｔａｉ（毛节泰）（ＤｅｐａｒｔｍｅｎｔｏｆＧｅｏｐｈｙｓｉｃｓ... 相似文献
8.
盆地环流型及冷湖的形成和消散的数值研究 总被引：3，自引：0，他引：3
本文建立了一个三维原始方程数值模式，模拟三维盆地中的环流，重点讨论在热力强迫环流型的转变过程中能量场的动量场的配置情况及环流演变过程。模拟结果表明，夜间地面强烈的辐射冷却过程引起盆地各坡面冷迳流的发展，盆地中成为冷空气湖，逆温层结建立。日出后对流边界层从大气低层向上发展，逆温从底部随之消蚀，仅在上层存在了夜间逆温残余，即所谓稳定核，上坡风在对流边界层发展，而稳定核内仍维持夜间下坡风环流。 相似文献
9.
G. Gross 《Boundary-Layer Meteorology》1987,40(4):311-327
A three-dimensional non-hydrostatic numerical model has been used to investigate the air flow and turbulence around a single tree.The results for velocity and turbulence distributions have been compared with available data from windtunnel experiments; the agreement is satisfactory.Simulations have been carried out for different meteorological conditions (wind speed, thermal stratification) as well as for different canopy characteristics (stem height, crown diameter, crown height, porosity).Dedicated to Prof. F. Wippermann on the occasion of his 65th birthday. 相似文献
10.
The present study is conducted to verify the short-range forecasts from mesoscale model version5 (MM5)/weather research and forecasting (WRF) model over the Indian region and to examine the impact of assimilation of quick scatterometer (QSCAT) near surface winds, spectral sensor microwave imager (SSM/I) wind speed and total precipitable water (TPW) on the forecasts by these models using their three-dimensional variational (3D-Var) data assimilation scheme for a 1-month period during July 2006. The control (without satellite data assimilation) as well as 3D-Var sensitivity experiments (with assimilating satellite data) using MM5/WRF were made for 48 h starting daily at 0000 UTC July 2006. The control run is analyzed for the intercomparison of MM5/WRF short-range forecasts and is also used as a baseline for assessing the MM5/WRF 3D-Var satellite data sensitivity experiments. As compared to the observation, the MM5 (WRF) control simulations strengthened (weakened) the cross equatorial flow over southern Arabian sea near peninsular India. The forecasts from MM5 and WRF showed a warm and moist bias at lower and upper levels with a cold bias at the middle level, which shows that the convective schemes of these models may be too active during the simulation. The forecast errors in predicted wind, temperature and humidity at different levels are lesser in WRF as compared to MM5, except the temperature prediction at lower level. The rainfall pattern and prediction skill from day 1 and day 2 forecasts by WRF is superior to MM5. The spatial distribution of forecast impact for wind, temperature, and humidity from 1-month assimilation experiments during July 2006 demonstrated that on average, for 24 and 48-h forecasts, the satellite data improved the MM5/WRF initial condition, so that model errors in predicted meteorological fields got reduced. Among the experiments, MM5/WRF wind speed prediction is most benefited from QSCAT surface wind and SSM/I TPW assimilation while temperature and humidity prediction is mostly improved due to latter. The largest improvement in MM5/WRF rainfall prediction is due to the assimilation of SSM/I TPW. The assimilation of SSM/I wind speed alone in MM5/WRF degraded the humidity and rainfall prediction. In summary the assimilation of satellite data showed similar impact on MM5/WRF prediction; largest improvement due to SSM/I TPW and degradation due to SSM/I wind speed. 相似文献
11.
Kyung-Hwan Kwak Jong-Jin Baik Sang-Hyun Lee Young-Hee Ryu 《Boundary-Layer Meteorology》2011,141(1):77-92
Urban surface and radiation processes are incorporated into a computational fluid dynamics (CFD) model to investigate the
diurnal variation of flow in a street canyon with an aspect ratio of 1. The developed CFD model predicts surface and substrate
temperatures of the roof, walls, and road. One-day simulations are performed with various ambient wind speeds of 2, 3, 4,
5, and 6 ms−1, with the ambient wind perpendicular to the north–south oriented canyon. During the day, the largest maximum surface temperature
for all surfaces is found at the road surface for an ambient wind speed of 3 ms−1 (56.0°C). Two flow regimes are identified by the vortex configuration in the street canyon. Flow regime I is characterized
by a primary vortex. Flow regime II is characterized by two counter-rotating vortices, which appears in the presence of strong
downwind building-wall heating. Air temperature is relatively low near the downwind building wall in flow regime I and inside
the upper vortex in flow regime II. In flow regime II, the upper vortex expands with increasing ambient wind speed, thus enlarging
the extent of cool air within the canyon. The canyon wind speed in flow regime II is proportional to the ambient wind speed,
but that in flow regime I is not. For weak ambient winds, the dependency of surface sensible heat flux on the ambient wind
speed is found to play an essential role in determining the relationship between canyon wind speed and ambient wind speed. 相似文献
12.
Several two-equation turbulence models using isotropic eddy viscosity and wall functions are assessed by solution of the neutral atmospheric boundary layer over a flat surface and wind flow over two- and three-dimensional models and real terrain. Calculations are presented for wind flow over the Sirhowy Valley in Wales, an embankment along the Rhine in Germany and the Askervein Hill in Scotland. Comparisons of predictions with previous work, and laboratory and field data, show that the RNG-based k– model gives the best agreement with respect to the flow profiles and length of the separated flow region. The results of this model are analyzed with a non-linear stress-strain relation to gauge the potential effect of turbulence anisotropy. 相似文献
13.
Observations of nocturnal slope flow have been made at two sites with quite different topography and vegetation. In both cases, continuous measurements of wind and temperature profiles were made from towers that extended through the depth of the katabatic flow. At the simpler site, which approximates a tilted plane, three towers were located at different distances down the slope to measure the development of slope flow with downslope distance.Slope flow depth, downslope wind speed, and temperature deficit are found to change with downslope distance at rates that are consistent with the predictions of Manins and Sawford's (1979) layer-averaged model of slope flow, while measured entrainment rates are found to be comparable to those predicted by Ellison and Turner's (1959) laboratory experiments. The depth of slope flow is found to be roughly 0.05 times the vertical drop from the top of the slope, a relationship that also follows from combining Manins and Sawford's model and Ellison and Turner's laboratory data. Analysis of the wind spectra and a simple numerical model suggest that the turbulent kinetic energy profiles in slope flow are dependent on the speed and direction of the ambient wind and can differ substantially from those found over flat terrain. At the more complex of the two measurement sites, the occurrence of slope flow was found to correlate well with a dimensionless number 5 that is a function of the ridge-top wind speed and of the strength and depth of the inversion and that is an estimate of the ratio of the buoyancy deficit to the external horizontal pressure gradient.Prepared for the U.S. Department of Energy under Contract DE-AC06-76RLO 1830 相似文献
14.
R. Dimitrova Jean-François Sini K. Richards M. Schatzmann M. Weeks E. Perez García C. Borrego 《Boundary-Layer Meteorology》2009,131(2):223-243
Micrometeorological conditions in the vicinity of urban buildings strongly influence the requirements that are imposed on
building heating and cooling. The goal of the present study, carried out within the Advance Tools for Rational Energy Use
towards Sustainability (ATREUS) European research network, is the evaluation of the wind field around buildings with walls
heated by solar radiation. Two computational fluid dynamics (CFD) codes were validated against extensive wind-tunnel observations
to assess the influence of thermal effects on model performance. The code selected from this validation was used to simulate
the wind and temperature fields for a summer day in a specific region of the city of Lisbon. For this study, the meteorological
data produced by a non-hydrostatic mesoscale atmospheric model (MM5) were used as boundary conditions for a CFD code, which
was further applied to analyze the effects of local roughness elements and thermodynamic conditions on the air flow around
buildings. The CFD modelling can also provide the inflow parameters for a Heating, Ventilation and Air Conditioning (HVAC)
system, used to evaluate the building energy budgets and to predict performance of the air-conditioning system. The main finding
of the present three-dimensional analyses is that thermal forcing associated with the heating of buildings can significantly
modify local properties of the air flow. 相似文献
15.
Leveraging the commercial CFD software FLUENT, the fine-scale three-dimensional wind structure over the Paiya Mountains on the Dapeng Peninsula near Shenzhen, a city on the seashore of South China Sea, during the landfall of Typhoon Molave has been simulated and analyzed. Through the study, a conceptual wind structure model for mountainous areas under strong wind condition is established and the following conclusions are obtained as follows： （1） FLUENT can reasonably simulate a three-dimensional wind structure over mountainous areas under strong wind conditions; （2） the kinetic effect of a mountain can intensify wind speed in the windward side of the mountain and the area over the mountain peak; and （3） in the leeward side of the mountain, wind speed is relatively lower with relatively stronger wind shear and turbulence. 相似文献
16.
针对2018年9月17日发生在广东省佛山市的一次台风龙卷过程,对比分析了EnKF和变分方法同化X波段相控阵雷达得到的风场结构。结果表明,EnKF方法和变分方法在同化了X波段相控阵雷达资料之后,都可以得到龙卷母体风暴的涡旋特征。相比之下,EnKF同化分析的涡旋强度更强,台风龙卷母体风暴及其周边三维风场的结构更加完整,与回波结构匹配更好。变分方法同化得到的流场不够连续,台风龙卷母体风暴的涡旋强度偏弱,弱回波区入流也明显偏弱,并不符合概念模型。而两种方法在没有同化相控阵雷达数据时,都无法产生龙卷母体风暴的流场特征。总体而言,相对于变分方法,EnKF同化系统在同化X波段相控阵雷达数据后可以产生更为合理的涡旋结构,台风龙卷母体风暴及其周边动力场结构更合理,这为以后X波段相控阵雷达的业务应用提供了思路。 相似文献
17.
An analytical model has been developed for the flow along a street canyon (of height H and width W), generated by an external wind blowing at any angle relative to the axis of the street. Initially, we consider the special
case of a wind blowing parallel to the street. The interior of the street is decomposed into three regions, and the flow within
each region is assumed to depend only on the external wind and the distance to the closest solid boundary. This decomposition
leads to two different flow regimes: one for narrow streets (H/W > 1/2) and one for wide streets (H/W < 1/2). The theoretical model agrees well with results obtained from numerical simulations using a Reynolds-Averaged Navier–Stokes
model. We then generalize the model to the case of arbitrary wind direction. Numerical solutions show that the streamlines
of the mean flow in the street have a spiral form, and for most angles of incidence, the mass flux along the street scales
on the component of the external wind resolved parallel to the street. We use this result to generalize the model derived
for wind blowing parallel to the street, and the results from this model agree well with the numerical simulations. The model
that has been developed can be evaluated rapidly using only very modest computing power, so it is suitable for use as an operational
tool. 相似文献
18.
In this experimental work both qualitative (flow visualisation) and quantitative (laser Doppler anemometry) methods were applied
in a wind tunnel in order to describe the complex three-dimensional flow field in a real environment (a street canyon intersection).
The main aim was an examination of the mean flow, turbulence and flow pathlines characterising a complex three-dimensional
urban location. The experiments highlighted the complexity of the observed flows, particularly in the upwind region of the
intersection. In this complex and realistic situation some details of the upwind flow, such as the presence of two tall towers,
play an important role in defining the flow field within the intersection, particularly at roof level. This effect is likely
to have a strong influence on the mass exchange mechanism between the canopy flow and the air aloft, and therefore the distribution
of pollutants. This strong interaction between the flows inside and outside the urban canopy is currently neglected in most
state-of-the-art local scale dispersion models. 相似文献
19.
A limited-area seven-layer physical-numerical model for the lower tropospheric region (surface - 1600m) is described. The grid interval, approximately 190km, is half that of the standard numerical weather-prediction grid used in the hemispheric free atmospheric operational model at the Air Force Global Weather Central (AFGWC). This model is an integral part of the complete AFGWC meso-scale (sub-synoptic) numerical analysis and prediction system and is used to provide greater horizontal and vertical resolution in both numerical analyses and forecasts.Important features of this boundary-layer model include: a completely automated objective analysis of input data; the transport of heat and moisture by three-dimensional wind flow; latent heat exchange in water substance phase changes; and eddy fluxes of heat and water vapor.Input data are conventional synoptic surface and upper air reports. Other operational AFGWC prediction models provide input in the form of horizontal wind components at the upper boundary and an estimate of cloudiness above the boundary layer. Forecasts for the lower boundary and surface layer are empirically derived. Despite some approximations which broadly simplify the real planetary boundary-layer processes, operational use for highly weather-sensitive Air Weather Service support indicates that the model is capable of producing accurate detailed forecasts for periods of up to 24h.A modified version of this paper was presented at the IUGG-IAMAP-AMS conference on Planetary Boundary Layers at Boulder, Colo., 18–21 March, 1970, and at the 5th annual Congress of the Canadian Meteorological Society, at Macdonald College, 12–14 May, 1971. 相似文献
20.
G. Zängl 《Meteorology and Atmospheric Physics》2003,83(3-4):237-261
Summary ?Numerical simulations of the south foehn in the region of Innsbruck are presented. They are semi-idealized in the sense that
realistic orography but idealized initial and boundary conditions are used. The focus of this study is on typical features
of the fully developed foehn, the breakthrough phase of the foehn and the diurnal cycle of the foehn. In addition, the impact
of the large-scale wind direction is examined, including conditions leading to shallow foehn.
The simulated flow fields have been found to be in very good agreement with observations except for a few minor details. In
the lower part of the Sill Valley (the valley going from the Brenner pass down to Innsbruck), the wind speed is significantly
higher than in the upper part. The acceleration can be traced back to the three-dimensional propagation of gravity waves excited
over the adjacent mountain ridges. The amplitude of the gravity waves over the various mountain ridges depends sensitively
on the wind direction, large wave amplitudes occurring only when the angle between the wind direction and the ridge line is
not too small. For southwesterly or south–southwesterly large-scale flow, wave amplitudes are significantly larger to the
east of Innsbruck than to the west. Foehn breakthrough at Innsbruck is usually preceded by a moderate westerly (downvalley)
wind that is restricted to a rather small area around Innsbruck. The simulations reveal that this so-called pre-foehn is mainly
a consequence of the gravity wave asymmetry, producing an asymmetric pressure perturbation with lower pressure to the east
of Innsbruck. Shallow foehn, defined as a foehn occurring when the large-scale flow at crest height (700 hPa) is approximately
westerly, is associated with relatively weak wave activity along the Sill Valley. It is found that at least a weak southerly
wind component below crest height is necessary to maintain a significant shallow foehn over a longer time.
Received October 10, 2001; accepted June 20, 2002
Published online: February 20, 2003 相似文献