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北京地区严重污染物状况下的大气边界层结构与参数研究 总被引：17，自引：3，他引：14
利用北京３２５ ｍ 铁塔资料对出现在１９９８ 年９ 月２６～３０ 日的一次严重污染过程的边界层结构和决定大气污染物扩散稀释的边界层参数作了分析和研究。分析发现, 这段时间边界层稳定层结占绝大多数, 白天在近地面的不稳定层结上还时有逆温盖, 另外在此期间风速较小。利用此资料还得到了北京严重污染状况下决定边界层湍流的一套基本物理参数 相似文献
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利用中国科学院大气物理研究所325 m铁塔15层风、温、湿梯度观测资料和3层超声资料,对2002年12月1~4日发生在北京地区的持续大雾天气过程进行近地面层大气边界层特征分析。结果表明,近地面大气边界层较大的相对湿度(70%)、较小的风速(3.0 m.s-1)和风速垂直切变(0.02 s-1)、稳定的层结结构以及较低的气温是北京持续大雾天气形成的主要原因。冷空气的侵入使得边界层相对湿度迅速减小,风速和风速垂直切变增大,破坏近地面大气边界层的结构,导致大雾的消散。分析还发现,大雾的维持与消散主要受风场等动力因素的影响,热力层结是大雾维持和消散的必要条件。冷空气的侵入自上而下影响平均风场,而对湍流风场的影响则是自下而上的。尺度分析结果表明,大雾期间,近地面边界层内中尺度动量通量和感热通量都大于湍流尺度的,中尺度动量通量与平均风速基本呈反相关;冷空气的侵入使得湍流通量显著加强,是导致大雾天气消失的主要原因。 相似文献
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夜间近地面稳定边界层湍流间歇与增温 总被引：1，自引：1，他引：1
在夜间晴空条件下，近地面大气湍流表现出很强的间歇性，这种间歇现象导致夜间气温短时的急剧下降，随后大幅度增温。近地面大幅度增温表明此时存在着很大的湍流热通量散度，常通量层的概念这时不存在。从各高度层温度和风速变化的曲线上分析，我们发现湍流大多在距离地面较高一点的高度上发生发展，然后向下层传递，尽管上层的湍流可能是由于下层的某一触发机制向上传递而引起的。湍流偶尔也出现自下向上传递的过程，但这一过程较少发生。湍流的这种上下传递说明稳定边界层大气经常处于非平衡状态，在运用相似理论研究稳定边界层大气结构时要特别注意这一情形。 相似文献
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本文在地转动量[1]近似下，采用与Agee[2]公式相近的分段常数来描述湍流粘性系数K及其一阶导数（湍流摩擦力所包含的两项和均得到考虑），求得了层结大气中的边界层风场分布和边界层顶垂直速度的解析表达式。计算结果表明；不稳定层结的K比稳定层结的大，且Ekman抽吸作用强；在边界层低层，不稳定层结的全风速比稳定层结的大，而在中层以上则相反。还有，摩擦力中的一阶导数项和二阶导数项量级相同，以往忽略一阶导数项的做法会导致在边界层低层，不稳定层结的全风速反而较小，这与事实不符。因而考虑一阶导数项将进一步完善边界层动力学的理论和应用。 相似文献
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应用含湍流频散效应的近地面层的运动方程求解了不同层结下的风速廓线，着重分析了湍流频散效应对近地面层平稳运动的影响。分析指出：湍流的频散效应对经典的幂律廓线一对数修正，该修正在不稳定层结时比稳定层时明显；利用相似理论也得到了该常数。 相似文献
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湍流频散对边界层风廓线的影响 总被引：2，自引：0，他引：2
应用包括湍流粘性和频散的新的Reynolds平均动量方程，分析了边界层的垂直风速廓线，发现包含湍流频散的地面层的风速廓线对经典的风廓线指数规律有一个对数规律的修改；而且在不稳定层结下比在稳定层结下，湍流的频散效应更为显；在中性条件下，指数规律退化为对数规律并且Karman常数被另外一个常数所代替，而这个新常数也可以通过相似理论来获得。 相似文献
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黑河绿洲区不均匀下垫面大气边界层结构的大涡模拟研究 总被引：11，自引：4，他引：7
采用RAMS模式中大涡模拟的方法,加入高分辨率的植被和土壤资料,模拟了黑河（张掖地区）不均匀下垫面条件下大气边界层演变过程。分析了模拟的地表通量、边界层的平均结构和湍流二阶量,并用黑河试验的观测资料检验了模式的模拟性能。结果表明,模拟的平均结构较好地展现了不均匀下垫面条件下边界层内从稳定层结到混合层发展,夹卷层形成,底层逆温层出现,混合层过渡到残留层等的演变过程,呈现出了从初始的稳定边界层发展到对流边界层,最后又形成夜问稳定边界层的日变化规律。湍流二阶量的分析显示,在非均匀下垫面条件下边界层内湍流二阶量的垂直分布与边界层的发展相对应,白天湍流二阶量出现两个峰值,分别位于近地层和混合层顶。与观测资料和现有研究的对比表明,RAMS中陆面模块（LEAF）地表参数不能较好地反映黑河地区的植被特征,模拟的白天地表感热和潜热通量偏小,气温白天偏低、夜间偏高,相对湿度也有偏差。 相似文献
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苏州东山冬季大气边界层结构特征及其对污染物浓度的影响 总被引：5，自引：1，他引：5
利用2015年1月15—27日在苏州东山气象观测站系留气艇观测数据以及细颗粒物浓度观测资料,对东山大气边界层结构特征及其对污染物垂直结构分布的影响进行分析研究。结果表明:苏州东山地区冬季空气污染过程的边界层结构演变比较典型,夜间稳定边界层高度约为200 m,白天最大边界层高度可达1 000 m。边界层内污染物垂直结构分布易受边界层高度的影响,较低的大气边界层高度可使细颗粒物在近地层持续累积;反之,边界层高度较高,湍流发展旺盛,颗粒物垂直分布均匀。夜间大气边界层稳定,逆温结构多发,导致近地面出现细颗粒物堆积。风的垂直结构对细颗粒物空间分布也存在显著影响,在风速较小的低空层细颗粒分布较多,而风速较大的中高层的分布较少。 相似文献
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利用小波变换（WT）对香港天文台飞机观测台风“妮妲”（1604）资料进行分析,研究在不稳定、不均匀的台风边界层中湍流涡旋的垂直传输作用。在0.1~5 Hz惯性子区内横风和顺风分量功率谱密度能较好符合-5/3幂律。小波分析显示:横风的小波功率谱峰值集中在1 km之下,顺风分量的小波功率谱峰值集中在1~6 km之间;眼区动量通量的主要贡献尺度为2.3 km,眼区外主要贡献尺度在1~2 km,中低层为较小尺度（< 1.0 km）;湍流功能(TKE)的生成尺度主要集中在4 km之下。这项研究定量描述了南海北部台风边界层各个区域湍流结构的差异特征,讨论了对台风边界层通量参数化的可能影响。 相似文献
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Wind-turbine-wake evolution during the evening transition introduces variability to wind-farm power production at a time of day typically characterized by high electricity demand. During the evening transition, the atmosphere evolves from an unstable to a stable regime, and vertical stratification of the wind profile develops as the residual planetary boundary layer decouples from the surface layer. The evolution of wind-turbine wakes during the evening transition is examined from two perspectives: wake observations from single turbines, and simulations of multiple turbine wakes using the mesoscale Weather Research and Forecasting (WRF) model. Throughout the evening transition, the wake’s wind-speed deficit and turbulence enhancement are confined within the rotor layer when the atmospheric stability changes from unstable to stable. The height variations of maximum upwind-downwind differences of wind speed and turbulence intensity gradually decrease during the evening transition. After verifying the WRF-model-simulated upwind wind speed, wind direction and turbulent kinetic energy profiles with observations, the wind-farm-scale wake evolution during the evening transition is investigated using the WRF-model wind-farm parametrization scheme. As the evening progresses, due to the presence of the wind farm, the modelled hub-height wind-speed deficit monotonically increases, the relative turbulence enhancement at hub height grows by 50%, and the downwind surface sensible heat flux increases, reducing surface cooling. Overall, the intensifying wakes from upwind turbines respond to the evolving atmospheric boundary layer during the evening transition, and undermine the power production of downwind turbines in the evening. 相似文献
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Yu Zhang Heping Liu Thomas Foken Quinton L. Williams Shuhua Liu Matthias Mauder Claudia Liebethal 《Boundary-Layer Meteorology》2010,136(2):235-251
During the Energy Balance EXperiment, the patch-by-patch, flood irrigation in a flat cotton field created an underlying surface
with heterogeneous soil moisture, leading to a dry (warm)-to-wet (cool) transition within the cotton field under northerly
winds. Moreover, the existence of an extremely dry, large bare soil area upstream beyond the cotton field created an even
larger step transition from the bare soil region to the cotton field. We investigated the turbulence spectra and cospectra
in the atmospheric surface layer (ASL) that was disturbed by large eddies generated over regions upstream and also influenced
by horizontal advection. In the morning, the ASL was unstable while in the afternoon a stable internal boundary layer was
observed at the site. Therefore, the turbulence data at 2.7 and 8.7 m are interpreted and compared in terms of interactions
between large eddies and locally generated turbulence under two atmospheric conditions: the unstable ASL beneath the convective
boundary layer (CBL) (hereafter the unstable condition) and the stable ASL beneath the CBL (hereafter the stable condition).
We identified the influences of multiple sizes of large eddies on ASL turbulence under both stratifications; these large eddies
with multiple sizes were produced over the dry patches and dry, large bare soil areas upstream. As a consequence of the disturbance
of large eddies, the broadening, erratic variability, and deviation of spectra and cospectra, relative to those described
by Monin–Obukhov similarity theory, are evident in the low- to mid-frequencies. Transfer of momentum, heat, and water vapour
by large eddies is distinctly observed from the turbulence cospectra and leads to significant run-to-run variations of residuals
of the surface energy balance closure. Our results indicate that these large eddies have greater influences on turbulence
at higher levels compared to lower levels, and in the unstable ASL compared to the stable ASL. 相似文献
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Results from radiosoundings, performed both over land and over sea, show that the ascent rate of a radiosounding balloon, the vertical velocity of the balloon, can be used to determine the height of the boundary layer. In many cases the balloon has a higher ascent rate in the boundary layer and a lower, less variable, ascent rate above. The decrease in ascending velocity appears as a jump at the top of the boundary layer. Two examples of potential temperature profiles for unstable stratification and one profile for stable conditions are shown with the corresponding ascent rates. A comparison between the boundary-layer height determined from potential temperature profiles and from ascent rates is presented for a larger dataset. The different ascent rates of the balloon in the boundary layer and above can be explained by a decrease in drag on the balloon in combination with a lowering of the critical Reynolds number in the boundary layer caused by turbulence. Hence, by simply logging the time from release of a radiosonde, it is possible to obtain additional information that can be used to estimate the height of both the unstable and stable boundary layers. 相似文献
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Unlike previous studies on wind turbulence spectrum in the planetary boundary layer, this investigation focuses on high-altitude （1-5 km） wind energy spectrum and turbulence spectrum under various weather conditions. A fast Fourier transform （FFT） is used to calculate the wind energy and turbulence spectrum density at high altitudes （1-5 km） based on wind profiling radar （WPR） measurements. The turbulence spectrum under stable weather conditions at high altitudes is expressed in powers within a frequency range of 2 × 10-5-10-3 s-1, and the slope b is between -0.82 and -1.04, indicating that the turbulence is in the transition from the energetic area to the inertial sub-range. The features of strong weather are reflected less obviously in the wind energy spectrum than in the turbulence spectrum, with peaks showing up at different heights in the latter spectrum. Cold windy weather appears over a period of 1.5 days in the turbulence spectrum. Wide-range rainstorms exhibit two or three peaks in the spectrum over a period of 15-20 h, while in severe convective weather conditions, there are two peaks at 13 and 9 h. The results indicate that spectrum analysis of wind profiling radar measurements can be used as a supplemental and helpful method for weather analysis. 相似文献
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Often, a combination of waves and turbulence is present in the stably stratified atmospheric boundary layer. The presence of waves manifest itself in the vertical profiles of variances of fluctuations and in low-frequency contributions to the power spectra. In this paper we study internal waves by means of a linear stability analysis of the mean profiles in a stably stratified boundary layer and compare the results with observed vertical variance profiles of fluctuating wind and temperature along a 200 m mast. The linear stability analysis shows that the observed mean flow is unstable for disturbances in a certain frequency and wavenumber domain. These disturbances are expected to the detectable in the measurements. It is shown that indeed the calculated unstable frequencies are present in the observed spectra. Furthermore, the shape of the measured vertical variance profiles, which increase with height, is explained well by the calculated vertical structure of the amplitude of unstable Kelvin-Helmholtz waves, confirming the contribution of waves to the variances. Because turbulence and waves have quite distinct transport properties, estimates of diffusion from measurements of variances would strongly overestimate this diffusion. Therefore it is important to distinguish between them. 相似文献
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L. Mahrt Dean Vickers Jim Edson James M. Wilczak Jeff Hare Jørgen Højstrup 《Boundary-Layer Meteorology》2001,100(1):47-61
The adjustment of the boundary layer immediately downstream froma coastline is examined based on two levels of eddy correlation data collected on a mast at the shore and six levels of eddy correlation data and profiles of mean variables collected from a mast 2 km offshore during the Risø Air-Sea Experiment. The characteristics of offshore flow are studied in terms of case studies and inter-variable relationships for the entire one-month data set. A turbulent kinetic energy budget is constructed for each case study.The buoyancy generation of turbulence is small compared to shear generation and dissipation. However, weakly stable and weakly unstable cases exhibit completely different vertical structure. With flow of warm air from land over cooler water, modest buoyancy destruction of turbulence and reduced shear generation of turbulence over the less rough sea surface cause the turbulence to rapidly weaken downstream from the coast. The reduction of downward mixing of momentum by the stratification leads to smaller roughness lengths compared to the unstable case. Shear generation at higher levels and advection of stronger turbulence from land often lead to an increase of stress and turbulence energy with height and downward transport of turbulence energy toward the surface.With flow of cool air over a warmer sea surface, a convective internal boundary layer develops downstream from the coast. An overlying relatively thick layer of downward buoyancy flux (virtual temperature flux) is sometimes maintained by shear generation in the accelerating offshore flow. 相似文献
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Hao Liu Renmin Yuan Jie Mei Jianning Sun Qi Liu Yu Wang 《Boundary-Layer Meteorology》2017,165(2):277-294
The scale properties of anisotropic and isotropic turbulence in the urban surface layer are investigated. A dimensionless anisotropic tensor is introduced and the turbulent tensor anisotropic coefficient, defined as C, where \(C = 3d_{3}\,+\,1 (d_{3}\) is the minimum eigenvalue of the tensor) is used to characterize the turbulence anisotropy or isotropy. Turbulence is isotropic when \(C \approx 1\), and anisotropic when \(C \ll 1\). Three-dimensional velocity data collected using a sonic anemometer are analyzed to obtain the anisotropic characteristics of atmospheric turbulence in the urban surface layer, and the tensor anisotropic coefficient of turbulent eddies at different spatial scales calculated. The analysis shows that C is strongly dependent on atmospheric stability \(\xi = (z-z_{\mathrm{d}})/L_{{\textit{MO}}}\), where z is the measurement height, \(z_{\mathrm{d}}\) is the displacement height, and \(L_{{\textit{MO}}}\) is the Obukhov length. The turbulence at a specific scale in unstable conditions (i.e., \(\xi < 0\)) is closer to isotropic than that at the same scale under stable conditions. The maximum isotropic scale of turbulence is determined based on the characteristics of the power spectrum in three directions. Turbulence does not behave isotropically when the eddy scale is greater than the maximum isotropic scale, whereas it is horizontally isotropic at relatively large scales. The maximum isotropic scale of turbulence is compared to the outer scale of temperature, which is obtained by fitting the temperature fluctuation spectrum using the von Karman turbulent model. The results show that the outer scale of temperature is greater than the maximum isotropic scale of turbulence. 相似文献