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1.
Observations of the Relation Between Upslope Flows and the Convective Boundary Layer in Steep Terrain 总被引：1，自引：1，他引：0
Slope flow mechanisms are crucial for the transport of air pollutants in complex terrain. Previous observations in sloping terrain showed upslope flows filling the entire convective boundary layer (CBL) and reducing air pollution concentrations by venting air pollutants out of the CBL into the free atmosphere. During the Pacific 2001 Air Quality Field Study in the Lower Fraser Valley, British Columbia, Canada, we observed slope flows during weak synoptic winds, clear skies, and strong daytime solar heating. With a Doppler sodar we measured the three wind components at the foot of a slope having an average angle of 19° and a ridge height of 780 m. We operated a scanning lidar system and a tethersonde at a nearby site on the adjacent plain to measure backscatter of particulate matter, temperature, wind speed, wind direction, and specific humidity. Strong daytime upslope flows of up to 6 m s−1 through a depth of up to 500 m occurred in the lower CBL, but with often equally strong and deep return flows in the upper part of the CBL. The mass transport of upslope flow and return flow approximately balanced over a 4-h morning period, suggesting a closed slope-flow circulation within the CBL. These observations showed that air pollutants can remain trapped within a CBL rather than being vented from the CBL into the free atmosphere. 相似文献
2.
T. J. Griffis S. D. Sargent X. Lee J. M. Baker J. Greene M. Erickson X. Zhang K. Billmark N. Schultz W. Xiao N. Hu 《Boundary-Layer Meteorology》2010,134(2):307-325
Impacts of different terrain configurations on the general behaviour of idealised katabatic flows are investigated in a numerical
model study. Various simplified terrain models are applied to unveil modifications of the dynamics of nocturnal cold drainage
of air as a result of predefined topographical structures. The generated idealised terrain models encompass all major topographical
elements of an area in the tropical eastern Andes of southern Ecuador and northern Peru, and the adjacent Amazon. The idealised
simulations corroborate that (i) katabatic flows develop over topographical elements (slopes and valleys), that (ii) confluence
of katabatic flows in a lowland basin with a concave terrainline occur, and (iii) a complex drainage flow system regime directed
into such a basin can sustain the confluence despite varying slope angles and slope distances. 相似文献
3.
Boundary-Layer Meteorology - Forest canopies have been shown to alter the dynamics of flows over complex terrain. Deficiencies have been found when tall canopies are represented in numerical... 相似文献
4.
Atmospheric flow over complex terrain, particularly recirculation flows, greatly influences wind-turbine siting, forest-fire behaviour, and trace-gas and pollutant dispersion. However, there is a large uncertainty in the simulation of flow over complex topography, which is attributable to the type of turbulence model, the subgrid-scale (SGS) turbulence parametrization, terrain-following coordinates, and numerical errors in finite-difference methods. Here, we upgrade the large-eddy simulation module within the Weather Research and Forecasting model by incorporating the immersed-boundary method into the module to improve simulations of the flow and recirculation over complex terrain. Simulations over the Bolund Hill indicate improved mean absolute speed-up errors with respect to previous studies, as well an improved simulation of the recirculation zone behind the escarpment of the hill. With regard to the SGS parametrization, the Lagrangian-averaged scale-dependent Smagorinsky model performs better than the classic Smagorinsky model in reproducing both velocity and turbulent kinetic energy. A finer grid resolution also improves the strength of the recirculation in flow simulations, with a higher horizontal grid resolution improving simulations just behind the escarpment, and a higher vertical grid resolution improving results on the lee side of the hill. Our modelling approach has broad applications for the simulation of atmospheric flows over complex topography. 相似文献
5.
山区复杂地形上区域大气质量模式的试验研究 总被引：3，自引：3，他引：3
由于复杂地形上的气流多变，所以，进行区域空气质量模拟是比较困难的。根据大气污染总量控制和环境规划的需要，发展了一种可适用于山谷城市的大气质量模式，该模式的主要特点；（１）采用目前尚少的复杂地形上的三维边界层模式作为大气扩散模式所需城三维边界层要素场；（２）用复杂地形上的三维以模式和斯扩散氏架源（包括面源）和主架源所造在的地面ＳＯ２浓度，然后将两者的模拟浓度在相应网各上叠加。验证结果表明，该混合模式 相似文献
6.
Pinhas Alpert 《Boundary-Layer Meteorology》1988,45(3):291-305
Three approaches for estimating meso-β (Δx=5–10 km) surface winds over complex terrain are applied to obtain best estimates of typical summertime surface flow in Israel, based on a detailed 3-D model, a one-level sigma model and a dense network of surface wind observations. A scheme for combining the three approaches is outlined and illustrated through two examples showing how the approaches complement each other. It is suggested that such a man-machine combination is best for estimation of surface winds over complex terrain. 相似文献
7.
四川地形复杂多样,暴雨频发,常诱发山洪、泥石流等灾害。在利用中尺度模式对复杂地形区域的暴雨进行研究时,模式水平分辨率的选取缺乏定量依据。为了揭示四川地形的复杂特征和给中尺度模式水平网格分辨率的选取提供定量依据,利用二维离散余弦变换,对四川地形高度场和暴雨分布场进行谱分解,根据暴雨分布特征分区讨论了四川盆地地形特征,同时利用地形谱方差和数值试验定量讨论了数值模式水平分辨率的选取问题,得到主要结论有:(1)二维离散余弦变换能较好地表现出研究区域各向异性的复杂特征;(2)雅安地区和四川盆地西北部的地形谱与降水谱有较好的同相关系,盆地东北部和盆地中部的地形谱与降水谱在波长较大处出现反相关系;(3)针对某个区域的地形特征,可以通过计算模式能分辨的地形方差与总地形方差的比值来确定合适的中尺度模式水平网格分辨率。 相似文献
8.
Renmin Yuan Minseok Kang Sung-Bin Park Jinkyu Hong Dongho Lee Joon Kim 《Meteorology and Atmospheric Physics》2011,110(3-4):123-133
An expanded planar-fit (PF) method over complex terrain is presented and applied to coordinate rotation of the eddy-covariance (EC) flux and vertical velocity estimation. Theoretical analysis indicates that PF coefficients depend on wind direction, and an expression of vertical velocity is deduced. We applied the theory using 1?year of observations from the KoFlux site in the Gwangneung Forest in Korea and investigated the influence of wind direction on the PF method. Then, we performed an expansion of the PF method to consider dependence of PF coefficients on wind direction and applied the PF method to every sector. The results show that the PF coefficients and tilt angles over complex terrain vary with wind direction. Two hundred 30-min data sets are sufficient to derive stable PF coefficients over hilly terrain for each sector. The relative difference in eddy-covariance flux between the general planar fit (GPF) and sector planar fit (SPF) is less than 10% for the scalar flux and about 18% for friction velocity. Vertical velocity and vertical advection (VA) terms were also calculated and compared using SPF and GPF methods, and a normal distribution and diurnal trend of real vertical velocity on clear days are presented. 相似文献
9.
气象保障是历届冬季奥林匹克运动会（冬奥会）成功举办的最重要条件之一。延庆赛区（位于延庆海陀山区）地形复杂、山高坡陡、垂直落差大,因而观测难度大、气象数据稀少,成为影响赛区精细化预报的核心因素,对冬奥气象服务提出了严峻挑战。为此,北京市气象局组织开展了冬奥海陀山综合气象观测,针对该区复杂地形和多尺度气象影响系统构建了包含中、小、微尺度的三维立体实时综合观测平台,观测要素涵盖了三维风场、温湿度场、云和能见度、近地面湍流与辐射等。综合观测将提高对复杂山区高影响天气特征和机理的认知,为改进和提高预报模式提供数据支撑。文中系统介绍了海陀山冬奥气象综合观测平台的科学目标、观测布局、观测内容以及观测平台在降雪过程中的初步应用,最后阐述了基于该观测进一步开展的研究计划。 相似文献
10.
Harlan D. Shannon George S. Young Michael A. Yates Mark R. Fuller William S. Seegar 《Boundary-Layer Meteorology》2002,104(2):167-199
An examination of boundary-layer meteorological and avian aerodynamic theories suggests that soaring birds can be used to measure the magnitude of vertical air motions within the boundary layer. These theories are applied to obtain mixed-layer normalized thermal updraft intensity over both flat and complex terrain from the climb rates of soaring American white pelicans and from diagnostic boundary-layer model-produced estimates of the boundary-layer depth zi and the convective velocity scale w*. Comparison of the flatland data with the profiles of normalized updraft velocity obtained from previous studies reveals that the pelican-derived measurements of thermal updraft intensity are in close agreement with those obtained using traditional research aircraft and large eddy simulation (LES) in the height range of 0.2 to 0.8 zi. Given the success of this method, the profiles of thermal vertical velocity over the flatland and the nearby mountains are compared. This comparison shows that these profiles are statistically indistinguishable over this height range, indicating that the profile for thermal updraft intensity varies little over this sample of complex terrain. These observations support the findings of a recent LES study that explored the turbulent structure of the boundary layer using a range of terrain specifications. For terrain similar in scale to that encountered in this study, results of the LES suggest that the terrain caused less than an 11% variation in the standard deviation of vertical velocity. 相似文献
11.
Bruce A. Egan Sc.D. 《Boundary-Layer Meteorology》1984,30(1-4):3-28
This paper reviews activities over the past nine years involving the evaluation, verification and development of atmospheric transport and diffusion models applied to air pollution assessments in complex/ mountainous terrain settings. Results from experiments performed at different complex terrain settings under stably stratified flow conditions have been emphasized. Comparisons of model predictions to observations are made. Physical modeling laboratory tests simulating flow conditions for full-scale experiments complement the data bases and provide information on systematic variations of modeling parameters and input conditions for mathematical model development purposes. Principal findings from these and other experiments on specific technical issues are summarized. 相似文献
12.
W. D. Neff 《Boundary-Layer Meteorology》1988,42(3):207-228
We examine methods for the interpretation of sodar facsimile records obtained in the study of complex terrain flows. Acoustic scattering theory is presented first and then interpreted using a simpolified second-order turbulence closure scheme. The use of this theory suggests the strong sensitivity of acoustic scatter to changes in the wind shear. With this introduction, detailed sodar facsimile records, temperature and wind profiles, and model calculations follow. Characteristic scattering patterns are described for simple drainage jets, complex basin flows, convection with a capping inversion, stratus, and dynamical instabilities. Examples are also shown of bistatic facsimile records detailing the strong temporal and spatial variability in small-scale turbulence. 相似文献
13.
Keith W. Ayotte 《Boundary-Layer Meteorology》1997,83(2):285-309
This paper describes an adjoint method for data assimilation intoupstream boundary conditions of numerical modelsusing optimal control theory. Mathematical formalisms are given along with the numerical implementation of the schemein a column model of the atmospheric boundary layer. The optimized mean and turbulence profiles are used as an upstream solutionin a model of turbulent flow in complex terrain. To contrast thiswith other methods, two solutions for flow over an isolatedhill are calculated, one with an optimized upstream solution andone with a simple surface-layer formulation for the upstream solution.These two solutions are compared to observations and analytical theory. The adjoint optimization method is shown to producesolutions of flow in complex terrain that are substantively differentat the two solutions, with the optimized solution giving more accurate results. 相似文献
14.
15.
局地地形起沙对沙尘模式的预报精度具有重要影响。基于狭管与下滑效应以及气流过山的已有研究成果,研究了中性层结与局地平缓地形条件下风速在这两种效应下次网格参数化问题,然后基于平坦地形的起沙公式、引入局地地形的摩擦速度,得到了相应的次网格起沙公式,最后对狭管效应、下滑效应以及两效应的叠加进行了理想试验。试验表明:(1)对于狭管效应的次网格参数化问题,风从狭管的阔口进(出)、窄口出(进)时,风速、跃移通量与起沙量均增大(减小);(2)下滑效应致使风速、跃移通量与起沙量均增大,且山脚增幅大于山坡;(3)对于两种效应的叠加,当气流从狭管的阔口进、窄口出时,风速、跃移通量和起沙量同时增大,山脚风速大于山坡,大粒径沙粒跃移通量增幅大于小粒径沙粒。反之,窄口进、阔口出时,出入口宽度之比存在一临界值,大于此临界值,风速减小;反之增大。而且,除了在山脚的小粒径沙粒在一定风速条件下跃移通量会增大外,其余情况均减少。最后,提出了本参数化方法与数值模式耦合的分算法与整算法。 相似文献
16.
17.
Daniel Reinert Volkmar Wirth Joachim Eichhorn Walter-Georg Panhans 《Boundary-Layer Meteorology》2007,125(1):109-132
This paper presents the dry version of a new large-eddy simulation (LES) model, which is designed to simulate air flow and
clouds above highly complex terrain. The model is three-dimensional and nonhydrostatic, and the governing equations are sound
filtered by use of the anelastic approximation. A fractional step method is applied to solve the equations on a staggered
Cartesian grid. Arbitrarily steep and complex orography can be accounted for through the method of viscous topography. The
dynamical model core is validated by comparing the results for a spreading density current against a benchmark solution. The
model accuracy is further assessed through the simulation of turbulent flow across a quasi two-dimensional ridge. The results
are compared with wind-tunnel data. The method of viscous topography is not restricted to moderately sloped terrain. Compared
to models using curvilinear grids, it allows this model to be applied to a much wider range of flows. This is illustrated
through the simulation of an atmospheric boundary-layer flow over a surface mounted cube. The results show that the dry model
version is able to accurately represent the complex flow in the vicinity of three-dimensional obstacles. It is concluded that
the method of viscous topography was successfully implemented into a micrometeorological LES model. As will be shown in Part
II, this allows the detailed study of clouds in highly complex terrain. 相似文献
18.
Monte-Carlo 法模拟复杂地形对扩散的影响 总被引：1，自引：0，他引：1
不考虑边界层中层结作用，引入Kao得到的复杂地形中的平均流场分布和近十年来PBL实验和理论研究导出的新的湍流统计量参数化关系，本文用Monte-Carlo模式模拟了复杂地形对扩散的影响，结果表明:地形的影响主要是迎风坡抬升和背风坡下沉；陡峭地形和平缓地形的影响不完全相同；在陡峭地形和大的平缓地形的背风坡能够形成空腔区，空腔区内出现闭合的浓度中心，且地形越陡峭，闭合浓度中心的范围越大；大地形对扩散的影响可以掩盖其下风方小地形的影响。 相似文献
19.
青藏高原大地形作用下,西南复杂地形区暴雨天气预报是一个十分重要和困难的科学问题。应用西南区域数值预报业务模式,结合业务常规观测和非常规观测资料,分析了2014年7月15日至17日发生在四川、贵州和重庆复杂地形下的一次由横槽诱发双低涡的贵州暴雨过程,得到:西南区域模式对这次暴雨过程的数值模拟结果与再分析资料有较好的对应关系,尤其是重现了降雨的落区、强度以及盆地涡与贵州涡的发生、发展过程。在暴雨过程中,两低涡垂直发展深厚,上升运动均伸展至对流层顶。涡度收支方面,盆地涡的发展主要源于涡度方程的散度项,而贵州涡的发展除了受散度项的显著影响外,平流项也起着重要作用。由于川渝盆地—云贵高原交界处地形、云贵高原横断山脉延伸区局地地形的作用,区域大气气旋式旋转的加强发展诱发了盆地涡和贵州涡。热力结构上,盆地涡的发生、发展在冷、暖气流交汇辐合区域内,而贵州涡则生成在暖区中,其降雨及加强更多地受到动力过程的影响。川渝盆地—云贵高原特殊的北低南高地形使高纬度干冷气流与低纬度暖湿气流交汇,形成强的上升运动,引发了盆地涡发展及其暴雨天气。云贵高原贵州特殊的西高东低地形导致来自低层的暖湿气流只能沿横断山脉边缘绕流,进入贵州西部的偏南气流与来自盆地涡西侧的偏东北气流汇合作用形成贵州涡,引发贵州暴雨天气。因此,局地地形与环流的相互作用是贵州涡生成及其引发暴雨过程的重要原因。 相似文献
20.
Albin Hammerle Alois Haslwanter Michael Schmitt Michael Bahn Ulrike Tappeiner Alexander Cernusca Georg Wohlfahrt 《Boundary-Layer Meteorology》2007,122(2):397-416
Carbon dioxide, latent and sensible heat fluxes were measured by means of the eddy covariance method above a mountain meadow
situated on a steep slope in the Stubai Valley in Austria, based on the hypothesis that, due to the low canopy height, measurements
can be made in the shallow equilibrium layer where the wind field exhibits characteristics akin to level terrain. In order
to test the validity of this hypothesis and to identify effects of complex terrain in the turbulence measurements, data were
subjected to a rigorous testing procedure using a series of quality control measures established for surface-layer flows.
The resulting high quality dataset comprised 36% of the original observations, the substantial reduction being mainly due
to a change in surface roughness and associated fetch limitations in the wind sector dominating during nighttime and transition
periods. The validity of the high quality dataset was further assessed by two independent tests: (i) a comparison with the
net ecosystem carbon dioxide exchange measured by means of ecosystem chambers, and (ii) the ability of the eddy covariance
measurements to close the energy balance. The net ecosystem CO2 exchange measured by the eddy covariance method agreed reasonably well with ecosystem chamber measurements. The assessment
of the energy balance closure showed that there was no significant difference in the correspondence between the meadow on
the slope and another one situated on flat ground at the bottom of the Stubai Valley, available energy being underestimated
by 28% and 29%, respectively. We thus conclude that, appropriate quality control provided, the eddy covariance measurements
made above a mountain meadow on a steep slope are of similar quality as compared to flat terrain. 相似文献