Determination of the Atmospheric Boundary Layer Height from Radiosonde and Lidar Backscatter

The height of the atmospheric boundary layer is derived with the help of two different measuring systems and methods. From radiosoundings the boundary layer height is determined by the parcel method and by temperature and humidity gradients. From lidar backscatter measurements a combination of the averaging variance method and the high-resolution gradient method is used to determine boundary layer heights. In this paper lidar-derived boundary layer heights on a 10 min basis are presented. Datasets from four experiments – two over land and two over the sea – are used to compare boundary layer heights from both methods. Only the daytime boundary layer is investigated because the height of the nighttime stable boundary layer is below the range of the lidar. In many situations the boundary layer heights from both systems coincide within ±200 m. This corresponds to the standard deviation of lidar-derived 10-min values within a 1-h interval and is due to the time and space variability of the boundary layer height. Deviations appear for certain situations and depend on which radiosonde method is applied. The parcel method fails over land surfaces in the afternoon when the boundary layer stabilizes and over the ocean when the boundary layer is slightly stable. An automatic radiosonde gradient method sometimes fails when multiple layers are present, e.g. a residual layer above the growing convective boundary layer. The lidar method has the advantage of continuous tracing and thus avoids confusion with elevated layers. On the other hand, it mostly fails in situations with boundary layer clouds     

数值模式中的大气边界层参数化方案综述

大气边界层对下垫面和自由大气之间的热量、动量和物质交换以及全球辐射的收支平衡有着非常重要的作用,数值模式中对边界层的模拟需要通过参数化方案表现出来。综述了数值模式中常用的边界层参数化方案,从闭合框架以及边界层内的重要物理过程这两个方面对各类方案进行了总结,并讨论了边界层参数化方案的发展方向。     

ADJUSTMENT OF WIND AND PRESSURE FIELDS IN THE BOUNDARY LAYER

The vertical transport of mass at the top of the boundary layer is considered as a link between theboundary layer and free atmosphere.The adjustment of the wind and pressure fields in the boundary layeris studied under the consideration of the interaction between the boundary layer and free atmosphere.Thevertical motion at the top of the boundary layer is evaluated.The results show that the distinguished differ-ences of the present results from classical Ekman layer do exist and they are discussed in the paper.     

地基微波辐射计探测大气边界层高度方法

采用2013年中国科学院大气物理研究所香河大气综合观测试验站的地基微波辐射计和激光雷达观测数据,以激光雷达探测的大气边界层高度为参考,分别利用非线性神经网络和多元线性回归方法建立微波亮温直接反演大气边界层高度的算法,并对比两种方法的反演能力, 同时分析非线性神经网络算法在不同时段及不同天气状况下反演结果的差异。结果表明:非线性神经网络算法的反演能力优于多元线性回归算法,其反演结果与激光雷达探测的大气边界层高度有较好一致性,冬、春季的相关系数达到0.83,反演精度比线性回归算法约高26%;对于不同时段和不同天气条件,春季的反演结果最好,晴空的反演结果好于云天; 四季和不同天气状况的划分也有利于提高反演精度。     

由非季风区向季风区过渡过程中大气边界层结构的变化分析

利用中国西北中部具有代表性的非季风区、夏季风影响过渡区和季风区的7个高空站的2013年夏季晴天07时、13时、19时（北京时）的大气边界层资料,通过分析大气边界层位温、比湿、风速的垂直结构,发现大气边界层结构及厚度在不同区域的分布特征:稳定边界层厚度、残余层顶高度和对流边界层厚度从非季风区、夏季风影响过渡区至季风区出现阶梯性大幅降低,从非季风区至夏季风影响过渡区,以及从夏季风影响过渡区至季风区,对流边界层厚度降幅依次为25.6%和81.8%,稳定边界层厚度降幅依次为58.3%和41.8%;在稳定边界层条件下,可观察到低空急流的存在,非季风区低空急流出现高度明显高于夏季风影响过渡区和季风区,且非季风区的低空急流风速也明显大于夏季风影响过渡区和季风区。通过分析与大气边界层发展最为密切的陆面热力因素在不同气候区的分布,净辐射值、日地-气温差最大值以及感热通量值在非季风区大于夏季风影响过渡区和季风区,从陆面热力过程为非季风区大气边界层厚度大于夏季风影响过渡区和季风区提供了理论依据。     

BOUNDARY LAYER GROWTH AND LAPSE RATE CHANGES DETERMINED BY LIDAR AND SURFACE HEAT FLUX IN SOFIA*

In this study the results from a boundary layer experiment,conducted in autumn 1991 over a flat,build-up urban area in Southeast Sofia,together with some models for mixed layer growth rates are used to investigate the layered structure of the vertical atmospheric stability distribution in the Sofia Valley.Lidar measurements of aerosol layer heights and morning boundary layer development are combined with surface eddy correlation measurements of kinematic heat and moisture fluxes,profiles of temperature and humidity,wind speed and wind direction.A diagnostic method is presented for determining vertical lapse rates using surface meteorological measurements and lidar returns observed during the transition from nighttime stable stratification to daytime convective boundary layer after the sunrise.     

A multi-limit formulation for the equilibrium depth of a stably stratified boundary layer

Currently no expression for the equilibrium depth of the turbulent stably-stratified boundary layer is available that accounts for the combined effects of rotation, surface buoyancy flux and static stability in the free flow. Various expressions proposed to date are reviewed in the light of what is meant by the stable boundary layer. Two major definitions are thoroughly discussed. The first emphasises turbulence and specifies the boundary layer as a continuously and vigorously turbulent layer adjacent to the surface. The second specifies the boundary layer in terms of the mean velocity profile, e.g. by the proximity of the actual velocity to the geostrophic velocity. It is shown that the expressions based on the second definition are relevant to the Ekman layer and portray the depth of the turbulence in the intermediate regimes, when the effects of static stability and rotation essentially interfere. Limiting asymptotic regimes dominated by either stratification or rotation are examined using the energy considerations. As a result, a simple equation for the depth of the equilibrium stable boundary layer is developed. It is valid throughout the range of stability conditions and remains in force in the limits of a perfectly neutral layer subjected to rotation and a rotation-free boundary layer dominated by surface buoyancy flux or stable density stratification at its outer edge. Dimensionless coefficients are estimated using data from observations and large-eddy simulations. Well-known and widely used formulae proposed earlier by Zilitinkevich and by Pollard, Rhines and Thompson are shown to be characteristic of the above interference regimes, when the effects of rotation and static stability (due to either surface buoyancy flux, or stratification at the outer edge of the boundary layer) are roughly equally important.     

BOUNDARY LAYER GROWTH AND LAPSE RATE CHANGES DETERMINED BY LIDAR AND SURFACE HEAT FLUX IN SOFIA

In this study the results from a boundary layer experiment,conducted in autumn 1991 over a flat,build-up urbanarea in Southeast Sofia,together with some models for mixed layer growth rates are used to investigate the layered struc-ture of the vertical atmospheric stability distribution in the Sofia Valley.Lidar measurements of aerosol layer heightsand morning boundary layer development are combined with surface eddy correlation measurements of kinematic heatand moisture fluxes,profiles of temperature and humidity,wind speed and wind direction.A diagnostic method is pres-ented for determining vertical lapse rates using surface meteorological measurements and lidar returns observed duringthe transition from nighttime stable stratification to daytime convective boundary layer after the sunrise.     

Similarity of large Reynolds number boundary layers

Similarity will exist for both the mean velocity and the turbulent shear stress of a turbulent boundary layer if the following conditions are met: (1) The surface shear is constant. (2) The boundary layer thickness parameters vary linearly with downstream distance. (3) The flow Reynolds number approaches infinity.These conditions may be nearly obtained in atmospheric type boundary layers. Measurements are presented from the Colorado State University Atmospheric Simulation Wind Tunnel which demonstrate the similarity. The wind-tunnel Reynolds number is from one to two orders of magnitude smaller than those of an atmospheric boundary layer.     

青藏高原纳木错湖区大气边界层结构分析

利用2007年8月8~19日期间系留气球低探空和GPS无线电探空资料,分析了纳木错湖区大气边界层高度、风、温、湿等要素的垂直结构。结果表明:纳木错湖的冷湖效应推迟了边界层湍流混合及对流边界层出现的时间,边界层高度日变化非常明显,对流边界层高度最高可达1750 m;在晴天条件下,边界层内湖陆风日变化非常明显,湖陆风控制范围常超过边界层高度,可达对流层中部;边界层内比湿变化呈V型变化,白天减小,夜间增大,早晨08:00出现峰值。     

A STUDY ON LOW－LEVEL ATMOSPHERIC STRUCTURE ON THE SEASIDE BORDERS TO THE WEST OF HAIKOU

In this paper, the observed data of low-level wind and temperature collected from western outskirts of Haikou city, Hainan Island, are analysed. Mean boundary layer structure, generation and development of ground-level inversion and inner boundary layer on the coastal area of interest, which is in China,s northern tropical area, are analysed. It is found that an inner thermal boundary layer can be produced under intense insolation in both dry and rainy seasons, and the mixing layer on the coast is remarkably deeper than that of inland.     

ON SIMILARITY AND THE TURBULENT STRUCTURE IN THE STABLE BOUNDARY LAYER

In the stably stratified boundary layer,the vertical flux profiles for momentum and heat can be obtained froman atmospheric boundary layer model which includes parameterization of the long-wave radiation.In addi-tion,the Monin-Obukhov similarity theory can be extended to the whole boundary layer by using the local tur-bulent scales L(z),U.(z)and 0.(z)in place of surface layer scales.The similarity predictions are ingood agreement with observational data.     

基于多种边界层方案的天津PM2.5集合预报试验

基于大气化学模式WRF/Chem采用4种边界层方案（YSU,BL,MYJ和MYN3）模拟2015年全年天津地区细颗粒物质量浓度演变趋势,分析不同边界层方案对天津地区PM_2.5质量浓度模拟和预报的影响,并构建多种边界层方案的集合预报产品,以期提高天津地区PM_2.5质量浓度预报效果。结果表明:大气化学模式的4种边界层方案在空气质量模拟中均有较好的适用性,PM_2.5模拟值与观测值相关系数达到0.76左右,晴空和大风天气BL方案表现较优,阴天和小风天气YSU和MYJ方案表现优于其他两种方案,综合所有过程没有任何单一方案具有显著优势。基于上述原因,该文开展多种边界层方案的天津空气质量集合预报试验,经过对2015年全年模拟值分析,多边界层方案和多气溶胶机制扰动的集合预报可以减小PM_2.5质量浓度预报的相对误差和均方根误差,降低重污染天气预报的漏报率,提升空气质量等级预报能力,在计算资源得到保证的基础上,是一种可以提升数值模式PM_2.5质量浓度预报能力的有效手段。     

基于风廓线雷达的广东登陆台风边界层高度特征研究

针对8个登陆广东省的热带气旋,利用经过数据质量控制的风廓线雷达连续、高时空分辨率的风场观测数据,对热带气旋边界层特征进行了分析。研究结果表明:热带气旋边界层中切向风速大值区垂直范围越大、风速越强、持续时间越久,则热带气旋强度越大、登陆后强度维持时间越久。眼区外入流层厚度越大,入流层气流越强,热带气旋登陆后强度维持时间则越久。风廓线雷达信噪比垂直梯度对大气湍流信息有一定的指示作用,对于入流层高度在2000 m以下的热带气旋,其入流层顶所在高度与信噪比梯度最大值所在高度相近,对于入流层较为深厚的热带气旋,用信噪比垂直梯度确定的边界层高度虽接近入流层顶高,但仍有一定差距。不同特点的热带气旋其边界层高度并不相同,对于登陆后强度迅速减弱的热带气旋边界层高度在500~1000 m;登陆后强度持续时间短的热带气旋,其边界层高度约1000~2000 m;登陆后强度持续时间长的热带气旋,其边界层高度在2000 m之上,最高可达5000~7000 m。这些结果加深了对登陆台风边界层高度演变特征的认识。     

北京一次浓雾过程的边界层结构及成因探讨

利用逐小时地面加密观测资料、系留气球探空资料、常规观测资料、NCEP再分析资料等对2004年11月30日至12月1日发生在北京的一次浓雾过程进行了分析。结果表明:浓雾过程发生在边界层有浅槽东移,地面为均压场、微风、入夜后迅速辐射降温的条件下;浓雾生成前、后近地层维持辐合区,有利于水汽的聚集;在浓雾发生发展的不同阶段,边界层中逆温层、湿度和风的分布是有差别的;从动力学的角度对温、湿场结构的形成原因进行了初步探讨,指出了与其它辐射雾的不同点。     

An Auxiliary Tool to Determine the Height of the Boundary Layer

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.     

利用TWP-ICE试验资料对比两种边界层参数化方案

利用高分辨率WRF单气柱模式,选取了两种边界层参数化方案(YSU,MYJ),对TWP-ICE(Tropical Warm Pool International Cloud Experiment)试验期间的个例进行数值模拟,比较了两种方案对边界层结构、云和降水模拟的影响。结果表明:季风活跃期,YSU方案模拟的湍流交换系数较小,湍流混合偏弱,边界层内热通量偏小,使地表热量和水汽不易向上输送,水汽含量在近地表明显偏多,而在边界层及其以上大气层具有显著的干偏差,因此该方案模拟的云中液态水和固态水含量偏低,云量偏少,降水率偏小;MYJ方案对于季风活跃期的边界层结构具有较好的模拟能力,其模拟的云和降水更为准确。季风抑制期,MYJ方案模拟的夜间边界层结构存在较大误差,这是因为该方案模拟的夜间湍流交换系数较大,湍流混合偏强,边界层内热通量偏大,模拟的位温和水汽混合比在边界层内随高度变化较小,而观测廓线在边界层内存在较大梯度。季风抑制期两种方案模拟的云和降水均比观测值偏多,方案之间的差异较小。     

Vorticity,divergence, and vertical velocity in a baroclinic boundary layer with a linear variation of the geostrophic wind

The Ekman-Taylor problem for the planetary boundary layer is solved in the case of a thermal wind which varies linearly with height. The upper boundary condition is a vanishing ageostrophic wind, while the lower boundary condition is continuity of the stress vector across the interface between the planetary boundary layer and the surface layer. The latter condition is used to determine the magnitude and the direction of the wind at the bottom of the Ekman layer.Theoretical hodographs are compared with observed hodographs based on five years of ohservations from Ship N in the Pacific, giving fair agreement.The divergence, the vorticity, and the vertical velocity are calculated through the Ekman layer with emphasis on differences between the classical barotropic and the baroclinic cases; these differences are significant, especially in the vertical velocities as compared to the standard approximation.An extension of the present study to include thermal stratification is desirable.     

正压边界层中的风压场相互调整

本文考虑正压边界层顶的垂直质量输送,将边界层与自由大气联系起来,研究这两层之间的风压场的相互作用所得到定常状态下的风压场,并算得了边界层顶的垂直速度。这些结果与经典Ekman边界层是有明显区别的。     

The influences of orography upon the flow within Ekman boundary layer under the approximation of geostrophic momentum

In this paper, the influences of orography on the boundary layer flow with the approximation of geostrophic momentum are studied. The wind velocity at the lower boundary will not always be zero when the orography exists. So the structure of the boundary layer flow, as well as the vertical velocity at the top of the boundary layer, is affected. There are three factors affecting the vertical motion at the top of the boundary layer: lifting due to orography; divergence due to Ekman flow, and advection of the geostrophic momentum. These effects and the features of the flow within the boundary layer are discussed in detail.