自由对流与稳定层结边界层风廓线的解析表达和边界层顶抽吸速度

基于近年来对自由对流和稳定边界层湍流交换特征的研究,求解边界层运动方程,得到这两种层结下边界层风的解析表达式.所得廓线与边界层特性参数符合观测特征.还求出了这二种层结下边界层顶抽吸速度的解析表达及其与某些参数的关系.结果表明,抽吸速度与层结有关,其特征可从物理上加以解释.     

欧洲风廓线仪计划

欧洲风廓线仪计划欧洲科技合作研究（ＣＯＳＴ７４）计划是由欧洲共同体委员会发起一项合作性大胆尝试。ＣＯＳＴ７４始于１９８７年，旨在促进欧洲风廓线仅站网的发展和建立。目前已有１２个欧洲国家参加了ＣＯＳＴ７４计划，它们是：奥地利、芬兰、德国、法国、意大利、...     

稳定大气近地面层的风和温度廓线

本文不做风和温度廓线相似性假设,使用最小二乘法分析位于粗糙、不均匀地形上北京气象专用塔在稳定条件下的平均风速和温度测量资料。结果表明,在近地面层,从弱稳定到强逆温的较宽的稳定层结范围内,对数加线性规律都是适用的;廓线参数βu和βθ不是常数,它们的数值随大气稳定度而变化。文中给出的经验公式表明:廓线参数随Ri的增大而减少,随L的增大而增大。在临界理查逊数的两侧,廓线参数随Ri的变化遵循不同的规律。文中还表明,廓线相似性假设仅对大气层结稳定度较弱时才是真实的;当稳定度增大时,廓线变成不相似,P值随Ri的增大而增大。     

边界层风廓线雷达测风精度分析

利用CLC-11-D型边界层风廓线雷达的5波束观测数据,对比分析了晴空、稳定性降水和对流性降水等不同类型气象条件下边界层风廓线雷达测风的准确性,并对2016年3月1日—2017年2月28日共计7300时次的晴空观测资料进行了测风质量评估,得出结论如下:在晴空条件下大气均匀稳定,水平风速和风向测量精度要优于稳定性降水和对流性降水天气,降水出现前后环境大气扰动较大是导致稳定性降水和对流性降水天气下测风精度较差的原因;150 m以下近地层高度的测风质量较差,与地杂波干扰较强有关;夏季有效探测高度最高可达6300 m左右,春秋季有效探测高度比较接近,分别为2000 m和2500 m左右,冬季有效探测高度最低,仅为1100 m左右;4个季节测风质量评估达标高度分别为900、4000、2200 m和1100 m,大气环境的湿度条件和水平风速、风向标准差的波动是影响测风质量评估的重要因素。     

观测高空风的新装备——风廓线雷达

风廓线雷达为最新发展起来的测风雷达,它能自动连续地获取高空风廓线。本文介绍风廓线雷达的原理、构造及性能,简要介绍了1985年美国PRE-STORM试验中风廓线雷达的试用结果,以及美国1989-1992年的试验网计划。     

边界层风廓线雷达测温系统设计

风廓线雷达在气象领域的应用越来越广泛，在风廓线雷达基础上增加电声测温系统（RASS）实现大气温度实时探测是一种经济有效的办法。文中介绍了已实现的某RASS系统设计，讨论了RASS测温的原理，针对RASS测温的精度、高度、影响因素等进行了性能分析，论述了系统的实现方案，最后给出了该RASS的实际测温结果和测温谱图，验证了该设计满足系统要求，能实现实时测温。     

移动式激光雷达边界层风廓线系统

研制了一种坚固的移动式激光测距气球跟踪系统来测量边界层的风廓线。这种移动式激光测距系统提供数字输出,并可由一名技术不太熟练的人员操作。需要另一名工作人员施放测风气球。测风间隔为50m,准确度为0.25m/s。在晴空条件下,系统的标称作用距离为3000m。     

HEST2007珠峰北坡风廓线观测研究

为了研究青藏高原南部喜马拉雅山区局地大气环流系统,继2006年HEST2006大气科学实验之后,2007年中国科学院大气物理研究所和中国科学院青藏高原研究所在珠穆朗玛峰北坡实施HEST2007综合观测.本文使用该观测实验中LAP-3000风廓线仪获得的绒布河谷内三维风场观测资料,并结合地面辐射资料,分析研究了该地区观测期间局地大气环流的日变化和逐日变化过程.研究表明,该地区局地环流系统,特别是沿河谷的轴向风,与其上空西风环流间存在非常紧密的联系,这种联系似乎与不同天气条件下喜马拉雅山区的大气辐射状况有关,即高层西风环流较强的阶段,地面辐射较强,激发出的局地环流也较强,反之亦然.     

高原地区风廓线雷达资料评估

在简述风廓线雷达原理的基础上,将风廓线雷达探测资料与探空资料进行对比分析,发现风速风向一致性较好,温度一致性较差。对风廓线资料总的数据获取率及不同天气条件下的数据获取率进行了统计,大理风廓线雷达边界层高度的数据获取率大于80%,在对流层低层以及边界层的探测能力要远远大于高层,高空雨季后的探测高度大于雨季前的探测高度。不同天气条件下低空的数据获取率差别不大,高空阴雨天的数据获取率大于晴天的数据获取率,阴雨天的探测高度大于晴天的探测高度。     

Performance of various similarity functions for nondimensional wind and temperature profiles in the surface layer in stable conditions

The linear functions for non-dimensional wind and temperature profiles are commonly used to describe the surface layer fluxes in atmospheric models. However, their applicability is limited to smaller values of the stability parameter z/L (where z is the height above ground and L is the Obukhov length) i.e. z/L < 1.0. These linear functions have been modified (Webb 1970, Quart. J. Roy. Meteor. Soc. 96, 67–90; Clarke 1970, Quart. J. Roy. Meteor. Soc. 96, 91–114; Hicks 1976, Quart. J. Roy. Meteor. Soc. 102, 535–551; Beljaars and Holtslag 1991, J. Appl. Meteorol. 30, 327–341; Cheng and Brutsaert 2005, Boundary-Layer Meteorol. 114, 519–538) over the years for calculating fluxes when z/L > 1.0 under strongly stable conditions. In view of this, the objective of the present study is to analyze the performance of these similarity functions to compute surface fluxes in stable conditions.The meteorological observations from the Cooperative Atmosphere-Surface Exchange Study (CASES-99) experiment are utilized for computing the surface fluxes in stable conditions. The computed fluxes are found to be reasonably close to those observed. The ratio of observed to computed fluxes reveals that the computed fluxes are close to the observations for all the similarity functions for z/L < 1.0 whereas the computed values show relatively a large scatter from observations for z/L > 1.0. The computed values of u and heat flux do not show significant differences from those observed at 99% confidence limit. The performance of all the similarity functions considered here is found to be comparable to each other in strongly stable conditions.     

A diagnostic study of wangara wind profiles in quasi-steady and near-neutral cases

Under the assumption of a geostrophic wind varying exponentially with height, profiles of four turbulence characteristics (Reynolds stress, eddy diffusivity, momentum mixing length, and energy dissipation rate) are evaluated for three cases of quasi-steady wind profile observations under near-neutral boundary layer conditions. These cases occurred during the Wangara Experiment organized by CSIRO at Hay, N.S.W., Australia, in 1967. It is shown that mean vertical motion and surface friction velocity significantly influence the evaluated profiles of the turbulence characteristics.This study was done while Zhang visited the Department of Meteorology, University of Wisconsin, from the Department of Meteorology, Nanjing University, China, and was completed when Zhang was affiliated with the National Center for Atmospheric Research.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Upper-air wind profiles investigation for tropospheric circulation study

Summary ¶Methods used to study the atmospheric circulation are essentially based on pressure classifications or geopotential fields. However, instead of using indirect means, a more direct measure of the atmospheric flow, i.e. the wind, appears preferable. In addition, it is admitted that, when explaining the weather variability, the combination of multiple level data can bring more information than studying just single-level characteristics. Thus, vertical profiles of wind are of great interest. The purpose of the article is twofold: first, to propose a method to classify this kind of data; second, to illustrate briefly the results obtained with the daily wind profiles acquired by upper-air soundings at a French meteorological station (Nancy), over a period of 11 years. The advantages of the method are: it is automatic and can easily be transposed in other areas; it provides a new type of information about the atmospheric circulation in the vertical dimension; it allows making easily the link between the circulation in the lower and upper troposphere.Received May 8, 2002; revised January 22, 2003; accepted March 15, 2003 Published online July 30, 2003     

A systematic algorithm for obtaining SODAR wind profiles

Summary Current methods of obtaining wind profiles from SODARs generally employ ad hoc strategies for Doppler spectrum peak selection, profile smoothing, and consistency checks. This paper addresses the problem of systematically obtaining vertical profiles of wind vectors from a SODAR. A new approach is to regard every spectrum frequency as a possible estimator of the radial wind component, but to weight these Doppler estimates according to the spectral power at each frequency. This allows the peak detection, smoothing, and assimilation of a priori information to be combined into a constrained linear inversion methodology. The inversion process also allows an estimation of signal-to-noise ratio, degrees of freedom, and information content versus height. Examples are given of profiles obtained using this new inverse method. The relationship to the physical limitations of the SODAR instrument and the atmosphere is discussed.     

Short-term prediction of local wind conditions

Using Numerical Weather Prediction (NWP) models it has been shown that they, combined with models (either physical or statistical) taking local effects into account, can be used to predict the wind locally better than the models commonly used today (as eg persistence). By local is meant at one distinct spot, as eg the location of a meteorological mast. The physical model of local effects takes the following into account: shelter from near-by obstacles, the effect of roughness changes and the effect of the local orography. The large-scale flow is linked to the surface flow by the geostrophic drag law, and the logarithmic wind profile. The predictions are made up to 36 hours ahead. The model is tested on data from 50 meteorological stations scattered all over Europe.     

Z-Less stratification under stable conditions

Turbulent fluctuations were measured at a height of 2.5 m in stable conditions over grass to investigate the variability of the second- and third-order moments involving temperature, humidity and vertical wind velocity. With the exception of the normalized second moment of temperature, very little variation of the normalized moments was found with changes in the dimensionless stability parameter =z/L, whereL is the Obukhov stability length. Such limited variation is expected for stable conditions, and the normalized second moment of temperature might have been affected by nonstationary conditions. In addition, the variability of the normalized moments was lessened by computing the turbulence statistics over 56 min, instead of 26 min. Values of third-order moments involving the vertical velocity were all close to zero.     

Similarity of scalars under stable conditions

The question whether two different scalars have the same behaviour in the surface layer under stable conditions is investigated. Similarity of two scalars is defined in terms of the equality of their corresponding dimensionless Monin-Obukhov similarity functions. Previous theoretical and experimental results concerning the issue are briefly reviewed: they are found to be contradictory. An analytical derivation of the square of the correlation coefficient between two scalars is obtained based on the correlation structure of the turbulent dissipation functions for stable conditions, when it can be assumed that the divergence of the vertical transport of scalar variance/covariance is negligible. The resulting expression elucidates some earlier conflicting results, and helps to establish the equality of the similarity functions for all scalars in the stable surface layer. A statistical analysis in the time domain is also performed using temperature and humidity turbulence data measured in nocturnal stable conditions during FIFE-89. Our results, both from the analytical derivation and the statistical analysis of turbulence data, confirm that under validity of the Monin-Obukhov similarity theory assumptions, the corresponding similarity functions for temperature and humidity are equal to within the statistical uncertainty of the measurements. An important consequence is that the eddy diffusivities of temperature and humidity are also equal.Now at SIMEPAR — Sistema Meteorológico do Paraná and UFPR — Universidade Federal do Paraná, Caixa Postal 318 CEP 80001-970, Curitiba PR Brazil.     

典型风场的多普勒天气雷达速度图象模拟与识别及暴雨实例分析

使用湖北新一代天气雷达平均散度反演产品,结合高空、地面和雷达观测资料,统计分析了短时强降水发生发展过程中大气低层辐合的演变特征,检验低层辐合的预警指示意义,并解释其天气意义。结果表明：低层辐合演变一般具有单波谷或双波谷特征,且中尺度特征明显。在强降水前期低层散度为辐合或由辐散转为辐合,强降水集中期低层辐合发展至最强,之后逐渐减弱,强降水后期低层转为辐散。低层辐合且明显增强可能具有预警指示意义。雷暴冷出流和低空急流加强对低层辐合有重要贡献。

     

Non-dimensional wind and temperature profiles in the atmospheric surface layer: A re-evaluation

Previous results of non-dimensional wind and temperature profiles as functions of ( = z/L) show systematic deviations between different experiments. These discrepancies are generally believed not to reflect real differences but rather instrumental shortcomings. In particular, it is clear that flow distortion has not been adequately treated in most previous experiments. In the present paper, results are presented from a surface-layer field experiment where great care was taken to remove any effects from this kind of error and also to minimize other measuring errors. Data from about 90 30-min runs with turbulence measurements at three levels (3, 6, and 14 m) and simultaneous profile data have been analysed to yield information on flux-gradient relationships for wind and temperature.The flux measurements themselves show that the fluxes of momentum and sensible heat are constant within ± 7% on average for the entire 14 m layer in daytime conditions and when the stratification is slightly stable. For more stable conditions, the flux starts to decrease systematically somewhere in the layer 6 to 14 m. From a large body of data for near-neutral conditions (¦¦ 0.1), values are derived for von Kármán's constant: 0.40 ± 0.01 and for _h at neutrally, 0.95 ± 0.04. The range of uncertainty indicated here is meant to include statistical uncertainty as well as the effect of possible systematic errors.Data for _m and _h for an extended stability range (1 > > – 3) are presented. Several formulas for _m and _h appearing in the literature have been used in a comparative study. But first all the formulas have been modified in accordance with the following assumptions: = 0.40 and ( _h ) _{= 0} = 0.95; deviations from this result in the various studies are due to incomplete correction for flow distortion. After new corrections are introduced, the various formulas were compared with the present measurements and with each other. It is found that after this modification, the most generally used formulas for _m and _h for unstable conditions, i.e., those of Businger et al. (1971) and Dyer (1974) agree with each other to within ± 10% and with the present data. For stable conditions, the various formulas still disagree to some extent. The conclusion in relation to the present data is not as clear as for the unstable runs, because of increased scatter. It is, however, found that the modified curve of Businger et al. (1971) for _h fits the data well, whereas for _m , Dyer's (1974) curve appears to give slightly better agreement.     

A case study of nocturnal wind and temperature profiles over the inhomogeneous terrain of Northern Germany with some considerations of turbulent fluxes

Soundings in the stably-stratified boundary layer were executed over the rough terrain of Northern Germany during a night with a low-level jet (LLJ) development. Vertical wind and temperature profiles were obtained at 5 m height intervals using a tethersonde transported up and down along a 300 m high radio tower by an elevator. From these profiles, turbulent fluxes of heat and momentum, coefficients of eddy diffusivity and boundary-layer parameters were estimated. The nocturnal mean state analysis agrees well with the second-order model results of Brost and Wyngaard (1978) and our own first-order numerical testing while the time histories of different profile groups are in accordance with the observations of Izumi and Barad (1963).