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1.
Summertime Characteristics of the Atmospheric Boundary Layer and Relationships to Ozone Levels over the Eastern United States 总被引：1，自引：0，他引：1
— This paper examines the spatial and temporal distributions of the mixing height, ventilation coefficient (defined as the product of mixing height and surface wind speed), and cloud cover over the eastern United States during the summer of 1995, using the high-resolution meteorological data generated by MM5 (Version 1), a mesoscale model widely used in air quality studies. The ability of MM5 to simulate the key temporal and spatial features embedded in the time series of observations of temperature, wind speed, and moisture is assessed using spectral decomposition methods. Also, mixing heights estimated from the MM5 outputs are compared with those derived from observations at a few locations where data with high temporal resolution are available in the Northeast. In addition, the uncertainties associated with the estimation of the evolution of the boundary layer during the morning time are examined. The results indicate that nighttime mixing heights averaged <200?m, rising to 1 km by 10 EST, and to about 2.5?km in the afternoon. Ventilation coefficients followed a similar diurnal pattern, increasing from 500?m2/s at night?to 15,000?m2/s in the afternoon; the increase due to the growing mixing height and increasing surface wind speeds. Spatial variability of these parameters was relatively small (coefficient of variation=0.25) at?night and in the afternoon when conditions were quasi-stationary, but increased (to 0.5) during morning?and evening hours when mixing heights and wind speeds were changing rapidly. Analyses of surface ozone observations from about 400 sites throughout the eastern United States indicate that days with numerous stations reporting surface ozone concentrations in excess of 80 ppb (i.e., “high ozone” days) generally had less daytime cloud cover, lower surface wind speeds, higher mixing heights, and lower ventilation coefficients than did comparable “low ozone” days. Such meteorological features are consistent with a synoptic anticyclone centered over the mid-south region (Kentucky, Tennessee). Low ozone days were characterized by more disturbed weather conditions (low pressure systems, fronts, greater cloud cover, and precipitation events). Ozone observations at two elevated platforms (～400?m agl) in Garner, NC, and Chicago, IL, indicated that ozone concentrations aloft were about 40% larger on “high ozone” days than on “low ozone” days. On average, high levels of ozone persist aloft for about 2 to 3 days. Strong vertical mixing in the daytime can bring this pool of upper-level ozone downward to augment surface ozone production. Since ozone can be transported downwind several hundred kilometers from its source region over this time scale, depending on upper-level winds, effective ozone control strategies must take into consideration spatial scales ranging from local to regional, and time scales of the order of several days. 相似文献
2.
Prabha R. Nair K. Susan George K. Parameswaran Marina Aloysius Denny P. Alappattu Mannil Mohan P.K. Kunhikrishnan 《Journal of Atmospheric and Solar》2009,71(17-18):1771-1783
In-situ measurements of number density, size distribution, and mass loading of near-surface aerosols were carried out at Kharagpur, a site on the eastern part of Indo-Gangetic Plains during the winter month of December 2004. The data have been used to investigate wintertime characteristics of aerosols and their effects on the occurrence of haze. The aerosol number density is found to be of the order of 109 m?3 and mass loading is ~265±70 μg m?3 (5–8 times that reported from south Indian sites). The diurnal patterns and day-to-day variations in aerosol number density and mass loading are closely associated with atmospheric boundary layer height. During haze events, the number density of submicron particles is found to be 2–5 times higher than that during non-hazy period. This could be attributed to the enhanced concentration of anthropogenic aerosols, low atmospheric boundary layer height/ventilation coefficient and airflow convergence. 相似文献
3.
《中国科学:地球科学(英文版)》2015,(8)
This paper revealed the climatic change characteristics of fog and haze of different levels over North China and Huang-Huai area(NCHH).It was found that the haze-prone period has changed from winter into a whole year,and the haze days(HD)in winter have increased significantly.The foggy days(FD)are half of HD.There are little difference on the number of days and trends of fog at various levels.The HD and FD show no obvious positive correlation until the 1980s.Fog has larger spatial scale,showing more in the south than in the north.Haze occurs mainly around large cities with a discrete distribution.In the background of weakened East Asian Winter Monsoon(EAWM)and sufficient particulate matter,the negative correlation between haze and wind speed is weakened,but the positive correlation between haze and moisture conditions(precipitation and humidity)is significantly strengthened.In recent years,small wind and variability appear frequently.Meanwhile,as the stable source and strong moisture absorption of the aerosol particles,the moisture condition becomes one key control factor in the haze,especially wet haze with less visibility.In contrast,the FD presents a stable positive correlation with precipitation and relative humidity,but has no obvious negative correlation with wind speed. 相似文献
4.
研究新一代中尺度气象模式WRF中两种大气边界层方案(MYJ,YSU)对沈阳冬季大气边界层结构模拟的影响,重点分析温度层结、低层风场、边界层高度等对污染物扩散有重要影响的气象要素.和观测数据的比对表明WRF基本能够模拟出温度风速的日变化特征,但模拟风速偏大.YSU方案由于模拟的边界层顶卷挟和边界层内混合作用较强,夜间接地逆温强度低于MYJ方案,逆温维持时间比MYJ方案短4小时,同时模拟边界层高度也高于MYJ方案,有利于污染物垂直扩散.边界层高度的3种计算方法中,湍流动能方法计算的边界层高度最高,Richardson数方法次之,位温方法得到的高度最低.Richardson数方法对临界值的选取较敏感. 相似文献
5.
— Air quality modeling in the marine environment requires a better understanding of air–sea interaction. The behavior of the sea is different from that of the land, particularly with respect to the aerodynamic roughness parameter which changes temporally and spatially as a function of wind-generated wave characteristics. Recent improved understanding in air–sea interaction as applied to topics in air quality modeling are discussed. They include stability characteristics, variation of the wind speed with height, mixing height, standard deviation of crosswind and vertical wind, and the eddy diffusion. These topics are synthesized for scientists and engineers who need to improve the air quality modeling for overwater applications. 相似文献
6.
随着近10年来北京城市化步伐的加快,城市规模迅速扩大,北京三环以外的地区已由20世纪七、八十年代的城郊非均匀下垫面发展成现在粗糙复杂的城区下垫面,市区建筑物相应增多、增密和增高,导致城区地面动力学粗糙度明显增大.本文统计分析了北京325 m气象塔1994年和1997～2003年夏季平均场观测资料,结果表明:(1)在受下垫面影响最为剧烈的近地层,风向逐年趋于紊乱,现在气象塔周围近地面的流场已经具备了典型城市粗糙下垫面的流场特征;(2)近地面夏季平均风速呈现非常明显的逐年递减的趋势,而且距离地表越近,平均风速逐年递减的趋势也越为显著,这种风速逐年递减的趋势直到63 m左右才不明显,说明现在气象塔47 m以下的观测资料反映的是城市冠层的流场特征,城市冠层厚度约在47～63 m之间;(3)随着北京城市化的发展,城区近地面的平均风速存在逐年递减的趋势,但阵风并不存在相似的递减趋势,表明城市冠层的抬升对阵风的影响并不显著. 相似文献
7.
The diurnal structure of the boundary layer during Indian summer monsoon period is studied using a one-dimensional meteorological
boundary layer model and the observations collected from the Monsoon Trough Boundary Layer Experiment conducted in 1990 at
Jodhpur, India. The model was initialized with the observed temperature profiles at 0530 LST on 17 July, 1990 at Jodhpur and
was run for 26 hours. The study is carried out with a geostrophic wind speed of 9.5 m s−1 corresponding to the strong wind simulation. The mean thermodynamic and wind structure simulated by the model are in good
agreement with those observed from 30 m tower. The computed surface layer characteristics such as the surface fluxes, TKE
and standard deviations of velocity components are found to be reasonably in good agreement with those based on turbulence
measurements. The shear and buoyancy budget computed from the model are also compared with the turbulence measurements. The
integrated cooling budget in the nocturnal boundary layer is examined. 相似文献
8.
DING Guoan CHAN Chuenyu GAO Zhiqiu YAO Wenqing LI Yoksheung CHENG Xinghong MENG Zhaoyang YU Haiqing WONG Kamhang WANG Shufeng MIAO Qiuju 《中国科学D辑(英文版)》2005,48(Z2)
The vertical structures and their dynamical character of PM2.5 and PM10 over Beijing urban areas are revealed using the 1 min mean continuous mass concentration data of PM2.5 and PM10 at 8, 100, and 320 m heights of the meteorological observation tower of 325 m at Institute of Atmospheric Physics, Chinese Academy of Sciences (IAP CAS tower hereafter) on 10―26 August, 2003, as well as the daily mean mass concentration data of PM2.5 and PM10 and the continuous data of CO and NO2 at 8, 100 (low layer), 200 (middle layer), and 320 m (high layer) heights, in combination with the same period meteorological field observation data of the meteorological tower. The vertical distributions of aerosols observed on IAP CAS tower in Beijing can be roughly divided into two patterns: gradually and rapidly decreasing patterns, I.e. The vertical distribution of aerosols in calm weather or on pollution day belongs to the gradually decreasing pattern, while one on clean day or weak cold air day belongs to the rapidly decreasing pattern. The vertical distributive characters of aerosols were closely related with the dynamical/thermal structure and turbulence character of the atmosphere boundary layer. On the clean day, the low layer PM2.5 and PM10 concentrations were close to those at 8 m height, while the concentrations rapidly decreased at the high layer, and their values were only one half of those at 8 m, especially, the concentration of PM2.5 dropped even more. On the clean day, there existed stronger turbulence below 150 m, aerosols were well mixed, but blocked by the more stronger inversion layer aloft, and meanwhile, at various heights, especially in the high layer, the horizontal wind speed was larger, resulting in the rapid decrease of aerosol concentration, I.e. Resulting in the obvious vertical difference of aerosol concentrations between the low and high layers. On the pollution day, the concentrations of PM2.5 and PM10 at the low, middle, and high layers dropped successively by, on average, about 10% for each layer in comparison with those at 8 m height. On pollution days, in company with the low wind speed, there existed two shallow inversion layers in the boundary layer, but aerosols might be, to some extent, mixed below the inversion layer, therefore, on the pollution day the concentrations of PM2.5 and PM10 dropped with height slowly; and the observational results also show that the concentrations at 320 m height were obviously high under SW and SE winds, but at other heights, the concentrations were not correlated with wind directions. The computational results of footprint analysis suggest that this was due to the fact that the 320 m height was impacted by the pollutants transfer of southerly flow from the southern peripheral heavier polluted areas, such as Baoding, and Shijiazhuang of Hebei Province, Tianjin, and Shandong Province, etc., while the low layer was only affected by Beijing's local pollution source. The computational results of power spectra and periods preliminarily reveal that under the condition of calm weather, the periods of PM10 concentration at various heights of the tower were on the order of minutes, while in cases of larger wind speed, the concentrations of PM2.5 and PM10 at 320 m height not only had the short periods of minute-order, but also the longer periods of hour order. Consistent with the conclusion previously drawn by Ding et al., that air pollutants at different heights and at different sites in Beijing had the character of "in-phase" variation, was also observed for the diurnal variation and mean diurnal variation of PM2.5 and PM10 at various heights of the tower in this experiment, again confirming the "in-phase" temporal/spatial distributive character of air pollutants in the urban canopy of Beijing. The gentle double-peak character of the mean diurnal variation of PM2.5 and PM10 was closely related with the evident/similar diurnal variation of turbulent momentum fluxes, sensible heat fluxes, and turbulent kinetic energy at various heights in the urban canopy. Besides, under the condition of calm weather, the concentration of PM2.5 and PM10 declined with height slowly, it was 90% of 8 m concentration at the low layer, a little lesser than 90% at the middle layer, and 80% at the high layer, respectively. Under the condition of weak cold air weather, the concentration remarkably dropped with height, it was 70% of 8 m concentration at the low layer, and 20%―30% at the middle and high layers, especially the concentration of PM2.5 was even lower. 相似文献
9.
本文运用近50 a来500 hPa层次上南极、赤道和北极位势高度以及南北半球西风指数的资料,分析了它们的时间演变规律及其相互间的关系.结果表明,南极位势高度显著下降;赤道位势高度显著上升.南极、赤道和北极位势高度都存在着显著的年际、年代际变化特征.总体上,南极位势高度与赤道位势高度有极其显著的负相关关系,北极与赤道的位势高度之间以及两极位势高度之间相关关系不显著;在共振的特定频率中,北极位势高度振荡落后于南极位势高度,赤道位势高度振荡又落后于两极位势高度振荡,气候变化最先开始的区域为南极地区.进一步分析表明,伴随着以上三个区域的位势高度趋势变化及其周期振荡,必然引起高空西风的增强与周期振荡.研究表明,南北两半球西风指数都存在显著的上升趋势,且存在显著的年代际变化特征.其中,南半球西风指数上升幅度较北半球大,其振荡落后于南极位势高度. 相似文献
10.
利用1998年夏季第2次青藏高原大气科学试验当雄观测站的边界层观测资料以及拉萨、改则和武汉等地探空资料,分析讨论西藏高原斜压对流边界层风、温、湿廓线的特征. 研究结果表明,高原地区白天对流边界层发展可高达2200m,显著超过中纬度平原地区和海面上对流边界层高度. 高原对流边界层中温度廓线具有较好的混合特征,湿度廓线有时在某一高度上出现湿度极大值. 高原对流边界层内热量和水汽收支分析表明,水平平流作用对边界层结构具有重要作用. 在对流边界层中平均风速垂直分布存在风切变现象. 水平温度梯度形成较强的斜压性是形成边界层风切变的主要原因. 相似文献
11.
Livio Belegante Doina Nicolae Anca Nemuc Camelia Talianu Claude Derognat 《Acta Geophysica》2014,62(2):276-289
In this study, we used boundary layer heights derived from lidar in Romania to validate the Weather Research Forecast (WRF) model improved by ARIA Technologies SA in the framework of ROMAIR LIFE project. Lidar retrievals were also compared to the retrievals from meteorological data, both modeled (Global Data Assimilation System; GDAS) and measured (microwave radiometry). Both the gradient and the wavelet covariance methods were used to compute the boundary layer height (BLH) from the range corrected lidar signal, and their equivalence was shown. The analysis was performed on 102 datasets, spread over all seasons and 3 years (2009–2011). A good agreement was found for the remote sensors (lidar and microwave radiometer) which are co-located and measure simultaneously. The correlation of the measured boundary layer height and the modelled one was 0.66 for the entire dataset, and 0.73 when considering daytime data, i.e., for a well defined boundary layer. A systematic underestimation of the boundary layer height by the WRF during non-convective periods (nocturne, stable atmosphere) was found. 相似文献
12.
下击暴流是雷暴天气产生的近地面短时强风,具有和大气边界层近地风显著不同的风场特征,其风荷载数值模拟方法也和常规风荷载模拟方法不同。在将下击暴流风速表达为时变的平均风速和调制的非平稳脉动风速之和的前提下,本文采用基于改进的OBV模型（Oseguera and Bowles／Vicroy（OBV））的方法来模拟平均风速,其平均风速直接由改进的OBV模型表达,而不同于已往研究中将平均风速表达为竖向风剖面与时间函数的乘积,并采用结合快速傅里叶变化的谐波叠加法来模拟调制的非平稳脉动风速。改进的OBV模型考虑了下击暴流的风暴中心移动和强度演化的影响,更准确地描述了下击暴流的实际物理过程。通过实例仿真,说明结果准确合理。 相似文献
13.
— This paper describes the meteorological processes responsible for the mean transport of air pollutants during the ENSO-related forest fires in Kalimantan, Indonesia from 00 UTC 21 September to 00 UTC 25 September, 1997. The Fifth Generation of the Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR) Mesoscale Model (MM5) is used to simulate three-dimensional winds at 6-hourly intervals. A nonhydrostatic version of the model is run using two nested grids with horizontal resolutions of 45 km and 15 km. From the simulated wind fields, the backward and forward trajectories of the air parcel are investigated using the Vis5D model.¶The results indicate that the large-scale subsidence over Indonesia, the southwest monsoon low-level flows (2–8 m s?1), and the shallow planetary boundary layer height (400–800 m) play a key role in the transport of air pollutants from Kalimantan to Malaysia, Singapore and Brunei. 相似文献
14.
C. O. Oluwafemi 《Pure and Applied Geophysics》1980,119(4):831-840
Helicopter measurements of solar irradiance and meteorological data within the atmospheric boundary-layer were made in Lagos during February 1979. Filter samples of aerosols were collected both during flight in February 1979 and at ground level in December 1978. Profile data on spectral aerosol optical depth were obtained and, from these, the aerosol extinction coefficient at two wavelengths (0.5 and 0.88 m) were calculated. Precipitable water was low and was contained mainly within the 750 m layer above ground, suggesting the establishment of a deep unstable boundary layer. Calculated channel energy depletions by aerosols show that, within the first 750 m of the surface, the 0·88 m might be more efficient at attenuating solar energy than 0·5 m. The lagoon (maritime) aerosol sample indicated a more monodisperse size-distribution than the dusty harmattan aerosol sample. 相似文献
15.
Robert M. Banta 《Acta Geophysica》2008,56(1):58-87
This paper reviews results from two field studies of the nocturnal stable atmospheric boundary layer (SBL) over the Great
Plains of the United States. Data from a scanning remote-sensing system, a High-Resolution Doppler Lidar (HRDL), provided
measurements of mean and turbulent wind components at high spatial and temporal resolution through the lowest 500–1000 m of
the atmosphere. This data set has allowed the characteristics of the low-level jet (LLJ) maximum (speed, height, direction)
to be documented through entire nights. LLJs form after sunset and produce strong shear in the layer below the LLJ maximum
or nose, which is a source of turbulence and mixing in the SBL. Simultaneous HRDL measurements of turbulence quantities related
to turbulence kinetic energy (TKE) has allowed the turbulence in the subjet layer to be related to LLJ properties. Turbulence
structure was found to be a function of the bulk stability of the subjet layer. For the strong-LLJ (> 15 m s−1), weakly stable cases the strength of the turbulence is proportional to the strength of the LLJ. For these cases with nearly
continuous turbulence in the subjet layer, low-level jet scaling, in which lengths are scaled by the LLJ height and velocity
variables are scaled by the LLJ speed, was found to be appropriate. For the weak-wind (< 5 m s−1 in the lowest 200 m), very stable boundary layer (vSBL), the boundary layer was found to be very shallow (sometimes < 10
m deep), and turbulent fluxes between the earth’s surface and the atmosphere were found to be essentially shut down. For more
intermediate wind speeds and stabilities, the SBL shows varying degrees of intermittency due to various mechanisms, including
shearinstability and other gravity waves, density currents, and other mesoscale disturbances. 相似文献
16.
An analytical expression for the 10 m drag law in terms of the 10 m wind speed at the maximum in the 10 m drag coefficient, and the Charnock constant is presented, which is based on the results obtained from a model of the air-sea interface derived in Bye et al. (2010). This drag law is almost independent of wave age and over the mid-range of wind speeds (5?17 ms?1) is very similar to the drag law based on observed data presented in Foreman and Emeis (2010). The linear fit of the observed data which incorporates a constant into the traditional definition of the drag coefficient is shown to arise to first-order as a consequence of the momentum exchange across the air-sea boundary layer brought about by wave generation and spray production which are explicitly represented in the theoretical model. 相似文献
17.
为了修正中尺度气象模式WRF(Weather Research and Forecasting model)对低层风速模拟的系统性误差,有学者在新版本WRF模式的YSU(Yonsei University)边界层参数化方案中加入了两个地形订正方法:Jiménez方法和UW(University of Washington method)方法.本文利用这两个地形订正方法,选取了两个时间段,对北京地区的地面气象要素以及气象要素垂直廓线进行了个例模拟研究,模拟结果和观测数据的比对表明在北京地区:是否采用地形订正,对地面温度的模拟几乎没有影响;采用地形订正后,模式对地面风速的模拟有明显的改进,两种方法对风速模拟的差别主要体现在山/丘陵地区;Jiménez方法在山/丘陵地区的模拟风速明显偏大,而采用UW方法进行订正后,模拟的风速减小,更接近观测值;两种方法在山谷地区对风速均有一定的过度订正.通过分析气象要素的垂直廓线发现,不同地形订正方法主要影响的是2000m以下的低层风速.总体而言,UW地形订正方法在北京地区更为适用,采用UW方法后,模拟得到的地面气象要素的各项统计参数基本达到了统计基准值. 相似文献
18.
本文主要利用全球定位下投式探空仪(dropsonde)资料和卫星云图资料,对2008年第15号超强台风蔷薇(Jangmi)边界层的热力和动力结构进行了分析,并且对其生命史中两个不同的时期的热力和动力结构特征进行了对比.结果表明:在内核区域中,距离眼越近,切向风越大,动力和热力边界层高度越低.边界层内,温度垂直递减率相比边界层以上更大;很多探空仪廓线中出现假相当位温(θse)垂直递减率与一般规律相反(即θse/z>0)的现象,并且能和径向风从流入转为流出以及Vr/z>0的高度很好的对应.对比生命史的不同时期,发现从台风发展的初始阶段到成熟阶段,在同一高度上切向风和径向风均有明显增大的趋势,径向流入层的厚度增大;台风内核区域的温度、比湿以及假相当位温都有增大的趋势,说明台风在发展增强的过程中从海表面获取了巨大的能量. 相似文献
19.
Intensive meteorological observations were carried out at three sites along the slope of Adélie Land, Antarctica, with the goal of documenting summertime meteorological features of the katabatic zone. Three observational sites were placed at 5 km (D10), 110 km (D47), and 210 km (D57) from the coast, and frequency distributions of meteorological parameters were obtained at each site. Some meteorological features at D47 and D57 (interior sites) were different than at D10 (the coastal site); namely, mean air temperatures averaged for the whole observational period showed more pronounced diurnal variations at the interior sites than at the coastal site. These variations could be represented by sinusoidal curves. Wind speeds also showed diurnal variations, whose extremes appeared several hours later than the temperature extremes. The prevailing wind direction for all sites was southerly, about 30° east of the fall line, with small variations in wind direction. The strength and the height of temperature inversions were examined in two different layers (0 to 50 m, 50 to 300 m) at D47. A strong, shallow inversion layer formed at night, however, completely vanished during the day. On the other hand, an upper level inversion whose strength was weak persisted. The katabatic characteristics of the surface wind found at D47 in summer could be due to this upper level temperature inversion.A contribution to I.A.G.O. (Interaction-Atmosphere-Glace-Ocean). 相似文献
20.
本文用对比方法研究声雷达定量探测温度结构系数的接收因子和衰减因子,分析了接收因子与某些气象要素的关系。分析结果表明,在63米高度上接收因子E=CT,a2/CT,d2与局地稳定度有关,它随稳定度的增大而增大;E值大小还与水汽量有关,E随水汽量的增大而增大;E值大小还与高度有关,它随高度增大而减小。分析结果还表明,在稳定条件下,衰减因子LE(E160/E63)的大小与160米高度上的水平风速有关,它随风速的增大而增大。文中还对气象条件对声雷达定量探测温度结构系数的影响进行了讨论。 相似文献