共查询到20条相似文献，搜索用时 31 毫秒
1.
The New Canadian Urban Modelling System: Evaluation for Two Cases from the Joint Urban 2003 Oklahoma City Experiment 总被引：2，自引：1，他引：1
A new Canadian numerical urban modelling system has been developed at the Meteorological Service of Canada to represent surface and boundary-layer processes in the urban environment. In this system, urban covers are taken into account by including the Town Energy Balance urban-canopy parameterization scheme in the Global Environmental Multiscale meteorological model. The new modelling system is run at 250-m grid size for two intensive observational periods of the Joint Urban 2003 experiment that was held in Oklahoma City, U.S.A. An extensive evaluation against near-surface and upper-air observations has been performed. The Town Energy Balance scheme correctly simulates the urban micro-climate, more particularly the positive nighttime urban heat island, and also reproduces the “cool” island during the morning but does not succeed in maintaining it during all of the daytime period. The vertical structure of the boundary layer above the city is reasonably well simulated, but the simulation of the nocturnal boundary layer is difficult, due to the complex interaction with the nighttime southerly low-level jet that crosses the domain. Sensitivity tests reveal that the daytime convective boundary layer is mainly driven by dry soil conditions in and around Oklahoma City and that the nighttime low-level jet reinforces the urban heat island in the first 300m through large-scale advection, leading to the development of a less stable layer above the city. 相似文献
2.
Sang-Hyun Lee 《Boundary-Layer Meteorology》2011,140(2):315-342
The vegetated urban canopy model (VUCM), which includes parametrizations of urban physical processes for artificial surfaces
and vegetated areas in an integrated system, has been further developed by including physical processes associated with grass-covered
surfaces in urban pervious surfaces and the photosynthesis effects of urban vegetation. Using measurements made from three
urban/suburban sites during the BUBBLE field campaign in 2002, the model’s performance in modelling surface fluxes (momentum
flux, net radiation, sensible and latent heat fluxes and storage heat flux) and canopy air conditions (canopy air temperature
and specific humidity) was critically evaluated for the non-precipitation and the precipitation days. The observed surface
fluxes at the urban/suburban sites were significantly altered by precipitation as well as urban vegetation. Especially, the
storage heat at urban surfaces and underlying substrates varied drastically depending on weather conditions while having an
important role in the formation of a nocturnal urban surface layer. Unlike the nighttime canopy air temperature that was largely
affected by the storage-heat release, the daytime canopy air conditions were highly influenced by the vertical turbulent exchange
with the overlying atmosphere. The VUCM well reproduced these observed features in surface fluxes and canopy air conditions
at all sites while performing well for both the non-precipitation and the precipitation days. The newly implemented parametrizations
clearly improved the model’s performance in the simulation of sensible and latent heat fluxes at the sites, more noticeably
at the suburban site where the vegetated area fraction is the largest among the sites. Sensitivity analyses for model input
parameters in VUCM elucidated the relative importance of the morphological, aerodynamic, hydrological and radiative/thermal
properties in modelling urban surface fluxes and canopy air conditions for daytime and nighttime periods. These results suggest
that the VUCM has great potential for urban atmospheric numerical modelling for a range of cities and weather conditions in
addition to having a better physical basis in the representation of urban vegetated areas and associated physical processes. 相似文献
3.
Yuling Wu Udaysankar S. Nair Roger A. PielkeSr. Richard T. McNider Sundar A. Christopher Valentine G. Anantharaj 《Boundary-Layer Meteorology》2009,133(3):367-389
Prior numerical modelling studies show that atmospheric dispersion is sensitive to surface heterogeneities, but past studies
do not consider the impact of a realistic distribution of surface heterogeneities on mesoscale atmospheric dispersion. While
these focussed on dispersion in the convective boundary layer, the present work also considers dispersion in the nocturnal
boundary layer and above. Using a Lagrangian particle dispersion model (LPDM) coupled to the Eulerian Regional Atmospheric
Modeling System (RAMS), the impact of topographic, vegetation, and soil moisture heterogeneities on daytime and nighttime
atmospheric dispersion is examined. In addition, the sensitivity to the use of Moderate Resolution Imaging Spectroradiometer
(MODIS)-derived spatial distributions of vegetation characteristics on atmospheric dispersion is also studied. The impact
of vegetation and terrain heterogeneities on atmospheric dispersion is strongly modulated by soil moisture, with the nature
of dispersion switching from non-Gaussian to near-Gaussian behaviour for wetter soils (fraction of saturation soil moisture
content exceeding 40%). For drier soil moisture conditions, vegetation heterogeneity produces differential heating and the
formation of mesoscale circulation patterns that are primarily responsible for non-Gaussian dispersion patterns. Nighttime
dispersion is very sensitive to topographic, vegetation, soil moisture, and soil type heterogeneity and is distinctly non-Gaussian
for heterogeneous land-surface conditions. Sensitivity studies show that soil type and vegetation heterogeneities have the
most dramatic impact on atmospheric dispersion. To provide more skilful dispersion calculations, we recommend the utilisation
of satellite-derived vegetation characteristics coupled with data assimilation techniques that constrain soil-vegetation-atmosphere
transfer (SVAT) models to generate realistic spatial distributions of surface energy fluxes. 相似文献
4.
D. Pavlidis G. J. Gorman J. L. M. A. Gomes C. C. Pain H. ApSimon 《Boundary-Layer Meteorology》2010,136(2):285-299
The computational fluid dynamics code Fluidity, with anisotropic mesh adaptivity, is used as a multi-scale obstacle-accommodating
meteorological model. A novel method for generating realistic inlet boundary conditions based on the view of turbulence as
a superposition of synthetic eddies is adopted. It is able to reproduce prescribed first-order and second-order one-point
statistics and turbulence length scales. The aim is to simulate an urban boundary layer. The model is validated against two
standard benchmark tests: a plane channel flow numerical simulation and a flow past a cube physical simulation. The performed
large-eddy simulations are in good agreement with both reference models giving confidence that the model can be used to successfully
simulate urban atmospheric flows. 相似文献
5.
Local Winds In A Valley City 总被引：1，自引：0，他引：1
Local winds were studied around a valley city, by using a high resolution two-dimensional mesoscale model forced by surface temperatures from a measurement campaign around Lanzhou City, China, during stagnant conditions. In the simulations nighttime winds are purely katabatic downslope winds without urban effects, despite the fact that the city is 6–7°C warmer than its surroundings all night. In contrast, daytime near-surface winds result from upslope flow resisted by an opposing simultaneous urban heat-island circulation (UHIC). Hence winds remain weak and variable around a city in a narrow valley during daytime. These conditions may lead to severe air quality problems day and night.The local circulations are sensitive to the widths of the valley and/or city,and also latitude, as is demonstrated by model experiments. Interestingly, in a flat and calm environment an extratropical daytime UHIC cell may turn into a weak `anti-UHIC' by the morning, due to frictional decoupling after sunset and subsequent inertial oscillation during the night, analogously tothe land breeze and nocturnal low-level jet formation. 相似文献
6.
城市空气污染数值预报系统CAPPS, 是在ADPIC的概念的基础上经过积分求得的大气平流扩散的多尺度箱格预报模型。它不需要污染源的源强资料就可预报出城市空气污染潜势指数 (PPI) 和污染指数 (API), 克服了由污染源调查本身具有的不确定性给城市空气污染的数值预报所带来的困难。该文对CAPPS系统在北京市和上海市进行数值预报的结果进行了分析检验, 并与国际上几种光化学污染预报模式的预报结果进行比较。结果表明, 就预报值与监测值的线性相关系数来说, CAPPS系统的预报水平与其他发达国家的模式预报水平相当。此外, CAPPS系统的污染指数等级预报准确率 (北京市和上海市) 平均达到61.5%。 相似文献
7.
冬季大气污染与天气条件分析及预报 总被引：1，自引：0，他引：1
本文用能见度的好坏来表征大气污染程度，通过对能见度与风速，风向的相关分析，从500hPa大气环流和地面气压场相结合入手，预报风速、风向及能见度，从而得到夜间和白天大气污染预报。 相似文献
8.
9.
西北干旱区夏季大气边界层结构及其陆面过程特征 总被引：18，自引：3，他引：15
在中国西北干旱区影响大气边界层形成和发展的气候环境和大气环流背景都具有一定特殊性.文中用外场观测试验资料,分析了位于西北干旱区的敦煌荒漠夏季大气边界层气象要素结构特征,发现该地区无论白天的对流边界层还是夜间的稳定边界层均比一般地区更深厚.在夏季晴天,夜间稳定边界层厚度超过900 m,最厚可以达到1750 m,其上的残余层一般能达到4000 m左右的高度;白天混合层最高达3700 m,混合层顶的逆温层顶盖的厚度大约450 m,甚至更厚,对流边界层厚度能够超过4000 m,对流边界层进入残余层后发展十分迅速.研究表明,白天深厚的对流边界层是夜间保持清晰而深厚的残余混合层的先决条件,夜间深厚的残余混合层又为白天对流边界层的发展提供了一个非常有利的热力环境条件.该地区经常性出现连续性晴天使得大气残余层的累积效应得以较长时间持续发展,创造了比较有利于大气对流边界层发展的大气热力环境条件.同时,该地区陆面过程和近地层大气运动特征也为这种独特的大气热力边界层结构提供了较好的支持.就该地区发展超厚大气对流边界层的物理机理而言,地表显著增温是强有力的外部热力强迫条件,近地层强感热通量提供了较充足的能量条件,较大的对流运动和湍流运动的速度是必要的运动学条件,大气残余层的累积效应提供了有利的热力环境条件. 相似文献
10.
开发了适合城市环境下的应急重气扩散模型——SLAB_URBAN模型,该模型能够对城市环境下重气的传输扩散过程进行模拟。模型的原理基于重气扩散浅层理论,采用了新的城市边界层和扩散参数的参数化方案。该方案考虑了城市冠层内特有的风和湍流扩散的特征,能够体现城市边界层和湍流对重气扩散的影响。对美国盐湖城Urban2000的城市扩散试验进行模拟,主要验证下风方向观测弧所观测到的气体最大小时平均浓度与源释放速率的比值。结果表明,模型能够比较好地模拟出下风方向上浓度的分布特征。另外,与国外同类城市扩散模型的比较来看,SLAB_URBAN模型的模拟能力居于前列。 相似文献
11.
为研究不同人为热源引入方案对城市边界层结构模拟性能的影响，以杭州地区为例，在区域边界层模式（RBLM）中引入一种新人为热源处理方案，即对城市中的人为热排放分层考虑，将低层的人为热源加入地表能量平衡方程，将高层人为热源分布与建筑物高度和密度联系起来，加入热量方程中，同时考虑了人为热源强度的日变化。数值试验结果表明，这是一种比较合理的处理方案。人为热源引入方案对城市边界层结构的影响表现在:气温、湍流动能增加，并通过湍流交换输送到较高层大气；大气不稳定度增加，混合层高度最高抬升了400 m；城市地区上升速度增加，热岛环流加强；白天人为热源一般为太阳辐射的10%～20%，对地气交换的影响较小。夜间没有了太阳辐射能量，对地气交换的影响比日间更明显；冬季低层湍流活动加强，湍能约增加40%，大气层结稳定度降低。 相似文献
12.
增暖背景下新疆昼夜降水的变化特征 总被引：1，自引：0，他引：1
利用新疆地区89个台站1961~2005年昼、夜降水观测数据,分析了该地区昼夜降水过程的时空演变特征,目的是认识这个地区在年降水增加背景下昼夜间降水过程的变化特征及趋势。研究结果表明:(1)1961~2005年,多年平均的降水量为夜大于昼,且昼、夜降水量均呈显著增加趋势;夜降水量增长趋势大于昼降水量,昼、夜年降水量增长趋势分别占年总降水增长趋势的49%、51%,这种变化在南、北疆存在明显的区域差异。昼、夜降水量都存在由少到多的显著突变,但两者发生突变时间不同,昼降水量发生突变的时间为1986年,而夜降水量的突变点却发生在1991年。(2)昼降水日数小于夜降水日数,且昼、夜降水日数都呈显著增加趋势,昼降水日数增加趋势大于夜降水日数。昼、夜降水强度都呈显著增大趋势,夜降水强度及其增长趋势均大于昼降水强度。降水量增加的主要原因是由于降水日数的增多,降水强度对降水量影响较小。(3)昼、夜毛毛雨日数都呈显著减少趋势,昼毛毛雨日数及其减少趋势均大于夜毛毛雨日数。而强降水的日数和强度均呈现增加趋势;昼、夜强降水量和各自的总降水量有很好的相关,强降水量对总降水量的影响很大。引起这些昼、夜间降水变化特征差异的原因有待于进一步研究。 相似文献
13.
Mathematical model for hermitized atmospheric dispersion in low winds with eddy diffusivities as linear functions of down wind distance 总被引：1，自引：0，他引：1
Summary In the present paper, an attempt is made for generalized the atmospheric diffusion operator. This can be accomplished by employing
the realizability procedure, to identify a surface operator, that ensures self-adjointness’ of the atmospheric diffusion operator.
The dispersion modeling in low wind speeds assumes importance because of the high frequency of occurrence and episodic nature
of these poor diffusion conditions. A steady-state mathematical model for hermitized model has been calculated for the dispersion
of air pollutants in low winds by taking into account the diffusion in the three coordinate directions and advection along
the mean wind. The eddy diffusivities have been parameterized in terms of downwind distance for near source dispersion (Arya,
1995). The constants involved in this parameterization are the squares of intensities of turbulence. An analytical solution
for resulting advection-diffusion equation with the physically relevant boundary conditions has been obtained. The solution
has been used to simulate the field tracer data collected at IIT Delhi in low wind convective conditions. 相似文献
14.
Simulation of urban climate with high-resolution WRF model: A case study in Nanjing, China 总被引：1，自引：0，他引：1
In this study, urban climate in Nanjing of eastern China is simulated using 1-km resolution Weather Research and Forecasting (WRF) model coupled with a single-layer Urban Canopy Model. Based on the 10-summer simulation results from 2000 to 2009 we find that the WRF model is capable of capturing the high-resolution features of urban climate over Nanjing area. Although WRF underestimates the total precipitation amount, the model performs well in simulating the surface air temperature, relative humidity, and precipitation frequency and inter-annual variability. We find that extremely hot events occur most frequently in urban area, with daily maximum (minimum) temperature exceeding 36°C (28°C) in around 40% (32%) of days. Urban Heat Island (UHI) effect at surface is more evident during nighttime than daytime, with 20% of cases the UHI intensity above 2.5°C at night. However, The UHI affects the vertical structure of Planet Boundary Layer (PBL) more deeply during daytime than nighttime. Net gain for latent heat and net radiation is larger over urban than rural surface during daytime. Correspondingly, net loss of sensible heat and ground heat are larger over urban surface resulting from warmer urban skin. Because of different diurnal characteristics of urban-rural differences in the latent heat, ground heat and other energy fluxes, the near surface UHI intensity exhibits a very complex diurnal feature. UHI effect is stronger in days with less cloud or lower wind speed. Model results reveal a larger precipitation frequency over urban area, mainly contributed by the light rain events (< 10 mm d?1). Consistent with satellite dataset, around 10?C20% more precipitation occurs in urban than rural area at afternoon induced by more unstable urban PBL, which induces a strong vertical atmospheric mixing and upward moisture transport. A significant enhancement of precipitation is found in the downwind region of urban in our simulations in the afternoon. 相似文献
15.
The modeling of atmospheric circulation in the Black Sea region using the WRF-ARW model for 30 summer days is considered to single out the contribution of the breeze component of wind speed. Assuming the quasiperiodic nature of breeze, the speed of daytime and nighttime breeze is computed for the whole region and for five separate areas on the coast. Specific features of the formation of daytime and nighttime breeze in these areas are distinguished. It is revealed that the presence of coastal mountains and the complex coastline determine the typical features of breeze development. 相似文献
16.
The diurnal surface temperature range(DTR) has become significantly smaller over the Tibetan Plateau(TP) but larger in southeastern China, despite the daily mean surface temperature having increased steadily in both areas during recent decades.Based on ERA-Interim reanalysis data covering 1979–2012, this study shows that the weakened DTR over TP is caused by stronger warming of daily minimum surface temperature(Tmin) and a weak cooling of the daily maximum surface temperature(Tmax); meanwhile, the enhanced DTR over southeastern China is mainly associated with a relatively stronger/weaker warming of Tmax/Tmin. A further quantitative analysis of DTR changes through a process-based decomposition method—the Coupled Surface–Atmosphere Climate Feedback Response Analysis Method(CFRAM)—indicates that changes in radiative processes are mainly responsible for the decreased DTR over the TP. In particular, the increased low-level cloud cover tends to induce the radiative cooling/warming during daytime/nighttime, and the increased water vapor helps to decrease the DTR through the stronger radiative warming during nighttime than daytime. Contributions from the changes in all radiative processes(over-2?C) are compensated for by those from the stronger decreased surface sensible heat flux during daytime than during nighttime(approximately 2.5?C), but are co-contributed by the changes in atmospheric dynamics(approximately-0.4?C) and the stronger increased latent heat flux during daytime(approximately-0.8?C). In contrast, the increased DTR over southeastern China is mainly contributed by the changes in cloud, water vapor and atmospheric dynamics. The changes in surface heat fluxes have resulted in a decrease in DTR over southeastern China. 相似文献
17.
A Simple Single-Layer Urban Canopy Model For Atmospheric Models: Comparison With Multi-Layer And Slab Models 总被引：26，自引：7，他引：26
Hiroyuki Kusaka Hiroaki Kondo Yokihiro Kikegawa Fujio Kimura 《Boundary-Layer Meteorology》2001,101(3):329-358
We developed a simple, single-layer urban canopy model, and comparedit to both multi-layer and slab models. Our single-layer model has thefollowing features: (a) It is a column model of energy and momentumexchange between an urban surface and the atmosphere, (b) it includesthe influence of street canyons, which are parameterized to representthe urban geometry, (c) it includes shadowing from buildings andreflection of radiation, and (d) it estimates both the surfacetemperatures of, and heat fluxes from, three surface types: roof, wall,and road. In the simulation of the single-layer model, the roof washottest during the daytime, but coolest from midnight to early morning.This is consistent with output from the multi-layer model and fieldobservations at a residential area on a clear, summer day. The diurnalvariation of the energy budget from the single-layer model agrees wellwith that from the multi-layer model. Our single-layer model'sperformance is nearly that of a multi-layer model for studyingmesoscale heat islands. Nevertheless, it is simply parameterized,and thus easily included in larger-scale atmospheric models. The slabmodel has the largest nighttime cooling rate of the three models. Toovercome this, it needs more adjustments than for the canopy models. 相似文献
18.
太阳能屋顶的安装预计能在一定程度上缓解城市化带来的能源危机及对城市热环境的破坏。利用耦合了城市单层冠层方案（UCM）的WRF模式,以南京2010年7月27日至8月5日夏季晴天微风天气为背景,模拟了不同发电效率的太阳能屋顶的安装对城市高温的缓解效应。结果表明:（1）太阳能屋顶可以通过削弱到达城市表面的太阳辐射使城市2 m高气温降低,随着发电效率的提高,降温效果更明显,且白天降温效果明显优于夜间;白天2 m高气温最大降低0.4-1.3℃,夜间降低0.2-0.5℃。（2）太阳能屋顶可使边界层内气温降低,白天在边界层400 m以下降温显著,夜间在边界层高度200 m以下降温显著;白天边界层内最大降温出现在中午前后,降温0.1-0.8℃,夜间边界层内最大降温0.5℃。（3）发电效率为40%时,模拟期间的发电量为18.1×109 kW·h。 相似文献
19.
Recent temperature projections for urban areas have only been able to reflect the expected change due to greenhouse-induced warming, with little attempt to predict urbanisation effects. This research examines temperature changes due to both global warming and urbanisation independently and applies them differentially to urban and rural areas over a sub-tropical city, Hong Kong. The effect of global warming on temperature is estimated by regressing IPCC data from eight Global Climate Models against the background temperature recorded at a rural climate station. Results suggest a mean background temperature increase of 0.67 °C by 2039. To model temperature changes for different degrees of urbanization, long-term temperature records along with a measureable urbanisation parameter, plot ratio surrounding different automatic weather stations (AWS) were used. Models representing daytime and nighttime respectively were developed, and a logarithmic relationship between the rate of temperature change and plot ratio (degree of urbanisation) is observed. Baseline air temperature patterns over Hong Kong for 2009 were derived from two ASTER thermal satellite images, for summer daytime and nighttime respectively. Dynamic raster modeling was employed to project temperatures to 2039 in 10-year intervals on a per-pixel basis according to the degree of urbanization predicted. Daytime and nighttime temperatures in the highly urbanized areas are expected to rise by ca. 2 °C by 2039. Validation by projecting observed temperature trends at AWS, gave low average RMS errors of 0.19 °C for daytime and 0.14 °C for nighttime, and suggests the reliability of the method. 相似文献
20.
为了探讨人为热源和城市绿化对城市边界层的影响,本文在RAMS模式中引入周期性日变化的人为热源和人工改变下垫面状况,初步模拟分析了人为热源和城市绿化对城市边界层结构的影响.结果表明:人为热源具有明显的增温效应,增强了城市的湍流交换,白天增加了大气不稳定度,促进了混合层的发展,夜间降低了大气稳定度,减弱了城市夜间逆温.城市绿化减小了地表反照率,增加了到达地面的净辐射,模拟期间土壤冻结,增加的净辐射其中一部分以感热的形式来加热大气;绿化后地气之间的湍流交换增强,增加了大气不稳定度,减弱了白天高空逆温;本文还讨论了不同绿化布局对白天高空逆温的影响以及人为热源和城市绿化之间的非线性相互作用. 相似文献