降雨强度对激光雷达测风精度的影响研究

多普勒激光雷达在大气、环境以及风能等领域得到越来越广泛的应用,但对于复杂天气下多普勒激光雷达的适用性仍然有待深入研究。为此本研究采用2020年8—10月期间位于福建三沙的地基多普勒激光雷达与边界层高塔所搭载的超声风温仪观测的风场数据进行对比,发现多普勒激光雷达在水平风速、风向方面具有稳定的高精度探测性能,与超声风温仪之间相关系数达到了0.948和0.984。相比之下,激光雷达垂直风速的探测误差较大,与超声风温仪之间相关系数仅有0.353。研究发现,降雨强度与激光雷达垂直风速误差呈正相关关系,强降雨下垂直风速偏差最大可达到9 m/s。     

Water vapour flux profiles in the convective boundary layer

Summary Water vapour flux profiles in the atmospheric boundary layer have been derived from measurements of water vapour density fluctuations by a ground-based Differential Absorption Lidar (DIAL) and of vertical wind fluctuations by a ground-based Doppler lidar. The data were collected during the field experiment LITFASS-2003 in May/June 2003 in the area of Lindenberg, Germany. The eddy-correlation method was applied, and error estimates of ±50 W/m² for latent heat flux were found. Since the sampling error dominates the overall measurement accuracy, time intervals between 60 and 120 min were required for a reliable flux calculation, depending on wind speed. Rather large errors may occur with low wind speed because the diurnal cycle restricts the useful interval length. In the lower height range, these measurements are compared with DIAL/radar-RASS fluxes. The agreement is good when comparing covariance and error values. The lidar flux profiles are well complemented by tower measurements at 50 and 90 m above ground and by area-averaged near surface fluxes from a network of micrometeorological stations. Water vapour flux profiles in the convective boundary layer exhibit different structures mainly depending on the magnitude of the entrainment flux. In situations with dry air above the boundary layer a positive entrainment flux is observed which can even exceed the surface flux. Flux profiles which linearly increase from the surface to the top of the boundary layer are observed as well as profiles which decrease in the lower part and increase in the upper part of the boundary layer. In situations with humid air above the boundary layer the entrainment flux is about zero in the upper part of the boundary layer and the profiles in most cases show a linear decrease.     

辽宁绥中地区海陆风的多普勒测风激光雷达观测与特征提取

2019年3月,利用相干多普勒测风激光雷达首次在辽东湾西部绥中地区进行了风廓线测量试验。根据研究区域海岸线走向采用风向的十六分位法定义局地海风和陆风,分析和提取海陆风特征验证了多普勒测风激光雷达在春季季风间断期间观测海陆风的可行性,并计算和分析了大气边界层湍流能量的变化以及回流水平变化等特性。结果表明：1）绥中地区春季存在明显的海陆风环流特征,测风激光雷达观测海陆风出现的时间与地面自动气象站观测的数据较为一致,符合海陆风日的定义。2）海陆风日发生时,水平局地回流指数（RF）较小,1.2 km以下的RF值小于0.5,使得污染物循环累积,较易形成雾霾天气;但是海风时大气边界层的高度可达1 km以上,有利于低层大气污染物向高层扩散,减轻低层大气污染。研究结果为该地边界层参数化方案的设计和污染的防治提供了参考依据。     

新型多普勒测风激光雷达Windcube的风参数观测与验证

2007年12月11～14日,中国科学院大气物理研究所与法国Leosphere公司在该研究所位于北京市北三环和北四环之间的325 m气象塔试验场内联合开展了一次测风激光雷达Windcube的外场演示试验.Windcube观测数据随后与325 m气象塔上的风杯风速仪测得的风速资料进行了对比,结果是:由两种手段获得的所有6...     

超大城市综合气象观测试验之测风激光雷达数据评估

为评估用于超大城市综合气象观测试验的测风激光雷达,从最大有效探测高度和数据获取率两方面对测风激光雷达的探测能力进行分析,同时使用测风激光雷达与深圳气象梯度观测塔的测风资料从不同观测高度、不同观测值等方面进行对比分析,结果表明：测风激光雷达与深圳气象梯度观测塔的风速、风向一致性较好,相关系数分别为0.96、0.99,平均绝对误差分别为0.54 m/s、9.95°,且不同高度层的测风结果也较为一致,但雨天和雾天条件对测风激光雷达的最大有效探测高度和数据获取率影响较大,设备探测能力受到一定的限制。     

多普勒激光雷达风场反演方法研究

采用三维变分同化反演(3DVAR)、 四维变分同化反演(4DVAR) 对多普勒激光雷达资料反演风场的方法进行了研究, 利用车载多普勒激光雷达在2008年残奥会测试赛期间外场试验取得的数据, 反演了海面10 m高度处的风场, 并将风场反演结果与浮标资料进行了对比分析, 结果表明: 3DVAR、4DVAR风场反演方法均能实现近海面风的精细化风场反演, 并能反映出风向的变化, 反演风场与浮标数据基本一致, 在风速较大的天气情况, 3DVAR与4DVAR反演风场的一致性要好于风速较小的天气情况; 4DVAR反演方法中以浮标资料作为背景场, 使得其与浮标的符合程度要好于3DVAR方法反演风场; 反演风场的风向与浮标风向具有很好的相关关系, 反演风场的风速与浮标风速具有一定的相关关系, 反演风场的风向、风速与浮标的风向、风速之间平均均方根误差和平均绝对误差表明, 这两序列之间具有一定差别, 在风速较小的天气情况下使用时需要注意。     

Turbulence statistics of a Kelvin–Helmholtz billow event observed in the night-time boundary layer during the Cooperative Atmosphere–Surface Exchange Study field program

An apparent shear flow instability occurred in the stably stratified night-time boundary layer on 6 October 1999 over the Cooperative Atmosphere–Surface Exchange Study (CASES-99) site in southeast Kansas. This instability promoted a train of billows which appeared to be in different stages of evolution. Data were collected by sonic anemometers and a high-frequency thermocouple array distributed on a 60 m tower at the site, and a high resolution Doppler lidar (HRDL), situated close to the tower. Data from these instruments were used to analyze the characteristics of the instability and the billow event. The instability occurred in a layer characterized by a minimum Richardson number Ri0.13, and where an inflection in the background wind profile was also documented. The billows, which translated over the site for approximately 30 min, were approximately L320 m in length and, after billow evolution they were contained in a layer depth H30 m. Their maximum amplitude, determined by HRDL data, occurred at a height of 56 m. Billow overturns, responsible for mixing of heat and momentum, and high-frequency intermittent turbulence produce kurtosis values above the Gaussian value of 3, particularly in the lower part of the active layer.     

Remote Sensing Of Three-Dimensional Winds With Elastic Lidar: Explanation Of Maximum Cross-Correlation Method

Maximum cross-correlation provides a method to remotely determine highly resolved three-dimensional fields of horizontal winds with elastic lidar throughout large volumes of the planetary boundary layer (PBL). This paper details the technique and shows comparisons between elastic lidar winds, remotely sensed laser Doppler velocimeter (LDV) wind profiles, and radiosonde winds. Radiosonde wind data were acquired at Barcelona, Spain, during the Barcelona Air-Quality Initiative (1992), and the LDV wind data were acquired at Sunland Park, New Mexico (N.M.), during the Border Area Air-Quality Study (1994). Comparisons show good agreement between the different instruments, and demonstrate the method useful for air pollution management at the local/regional scale. Elastic lidar winds could thus offer insight into aerosol and pollution transport within the PBL. Lidar wind fields might also be used to nudge or improve initialization and evaluation of atmospheric meteorological models.     

Coherent Doppler Lidar Measurements of Wind Field Statistics

Coherent Doppler lidar measurements of wind statistics in the boundary layer are presented. The effects of the spatial averaging by the lidar pulse are removed using theoretical corrections and computer simulations. This permits unbiased estimates of velocity variance, spatial velocity structure functions, energy dissipation rate, and other point statistics of the velocity field.     

On the relation between surface wind and pressure gradient,especially in lower latitudes

Observations show that the angle between surface wind and isobar increases equatorward in low latitudes while the ratio of surface to geostrophic wind speed decreases. With the use of Southern Hemisphere winter fields of surface pressure and temperature over the oceans, and Rossby number similarity theory (including the effects of baroclinicity) in several different forms, the expected latitudinal variation of the angle and ratio has been computed. A check has also been made of mean ATEX and BOMEX data. It appear that the variations with latitude are probably mainly due to baroclinicity. With this factor taken into account, similarity theory fairly adequately explains the observations.A recently proposed form of similarity theory based on the assumption of very strong momentum mixing in the boundary layer was also tested. It predicts the equatorward increase of the angle, even without baroclinicity. Quantitatively the results of the test are not in good agreement with observation. However, the strong convective mixing assumed in the theory does not generally occur over the oceans, and this test must be regarded as inconclusive.     

Estimate of Boundary-Layer Depth Over Beijing,China, Using Doppler Lidar Data During SURF-2015

Planetary boundary-layer (PBL) structure was investigated using observations from a Doppler lidar and the 325-m Institute of Atmospheric Physics (IAP) meteorological tower in the centre of Beijing during the summer 2015 Study of Urban-impacts on Rainfall and Fog/haze (SURF-2015) field campaign. Using six fair-weather days of lidar and tower data under clear to cloudy skies, we evaluate the ability of the Doppler lidar to probe the urban boundary-layer structure, and then propose a composite method for estimating the diurnal cycle of the PBL depth using the Doppler lidar. For the convective boundary layer (CBL), a threshold method using vertical velocity variance \((\sigma _w^2 >0.1\,\hbox {m}^{2}\hbox {s}^{-2})\) is used, since it provides more reliable CBL depths than a conventional maximum wind-shear method. The nocturnal boundary-layer (NBL) depth is defined as the height at which \(\sigma _w^2\) decreases to 10 % of its near-surface maximum minus a background variance. The PBL depths determined by combining these methods have average values ranging from \(\approx \)270 to \(\approx \)1500 m for the six days, with the greatest maximum depths associated with clear skies. Release of stored and anthropogenic heat contributes to the maintenance of turbulence until late evening, keeping the NBL near-neutral and deeper at night than would be expected over a natural surface. The NBL typically becomes more shallow with time, but grows in the presence of low-level nocturnal jets. While current results are promising, data over a broader range of conditions are needed to fully develop our PBL-depth algorithms.     

基于斐索干涉仪的直接探测多普勒测风激光雷达

提出结合多光束斐索(Fizeau)干涉仪和CCD探测器的条纹图像技术,测量地球边界层下的三维风场的直接探测多普勒激光雷达技术.在分析Fizeau干涉仪的物理特性和光谱特性以及影响测量多普勒频移的因数和改进方法的基础上,提出一套切合实际的直接探测多普勒激光雷达系统参数.并利用该参数进行性能评估分析,模拟不同干涉仪参数对风速精度的影响,得出一个优化的干涉仪物理参数.模拟结果显示,系统可以获得小于1 m s-1的水平风速精度.这些分析,为建立实际的激光雷达系统提供设计依据.     

Galion激光测风雷达探测性能分析

Galion激光雷达是应用第二代技术的激光雷达设备,具备对全天空、全角度的扫描能力,目前是市场上唯一的三维扫描设备。本文利用深圳356 m梯度塔与锡林浩特100 m梯度塔的观测数据分析了Galion激光雷达的探测性能,并得出以下结论：PPI模式下,深圳激光雷达与测风塔测得风速相关系数为0.85,风向相关系数为0.9;锡林浩特激光雷达与测风塔测得风速相关系数为0.9,风向相关系数为0.95;此外,雷达在各个角度探测的结果相关性都较好,说明激光雷达在PPI模式下具有很好的探测性能。     

一次暴雨过程大气边界层结构的数值分析

1979年7月28日河北唐山地区的强暴雨,10小时总降水量达430mm,降水强度大,从时间和空间上都非常集中。这次太平洋副热带高压北侧暖区发生的强暴雨引起国内气象界的普遍重视。游景炎,陆一强等对这次暴雨过程的大尺度环境、中尺度结构进行了详细分析并分别讨论了边界层急流、强对流性云团以及地形等的作用。游景炎根据地面天气图的分析,发现明显的雷暴高压和中尺度低压。这种中尺度系统在大气边界层内如何表现呢?这次暴雨系统延伸多高呢?各种物理量输送和分布的特性     

Doppler Lidar Measurements of Vertical Velocity Spectra in the Convective Planetary Boundary Layer

We utilized a Doppler lidar to measure spectra of vertical velocity w from 390m above the surface to the top of the daytime convective boundary layer (CBL). The high resolution 2μm wavelength Doppler lidar developed by the NOAA Environmental Technology Laboratory was used to detect the mean radial velocity of aerosol particles. It operated continuously during the daytime in the zenith-pointing mode for several days in summer 1996 during the Lidars-in-Flat-Terrain experiment over level farmland in central Illinois, U.S.A. The temporal resolution of the lidar was about 1 s, and the range-gate resolution was about 30m. The vertical cross-sections were used to calculate spectra as a function of height with unprecedented vertical resolution throughout much of the CBL, and, in general, we find continuity of the spectral peaks throughout the depth of the CBL. We compare the observed spectra with previous formulations based on both measurements and numerical simulations, and discuss the considerable differences, both on an averaged and a case-by-case basis. We fit the observed spectra to a model that takes into account the wavelength of the spectral peak and the curvature of the spectra across the transition from low wavenumbers to the inertial subrange. The curvature generally is as large or larger than the von Kármán spectra. There is large case-to-case variability, some of which can be linked to the mean structure of the CBL, especially the mean wind and the convective instability. We also find a large case-to-case variability in our estimates of normalized turbulent kinetic energy dissipation deduced from the spectra, likely due for the most part to a varying ratio of entrainment flux to surface flux. Finally, we find a relatively larger contribution to the low wavenumber region of the spectra in cases with smaller shear across the capping inversion, and suggest that this may be due partly to gravity waves in the inversion and overlying free atmosphere.     

A scaling parameter for turbulence in baroclinic convective boundary layers

The influence of baroclinicity on the structure and levels of turbulence in the convective boundary layer depends on both the magnitude and orientation of geostrophic wind shear and the level of convection. The geostrophic Richardson number, a Richardson number defined in the present work and based on the geostrophic wind shear, is shown to be a single non-dimensional parameter which determines the influence of baroclinicity on convective turbulence structure.     

Comparing mixing-length models of the diabatic wind profile over homogeneous terrain

Models of the diabatic wind profile over homogeneous terrain for the entire atmospheric boundary layer are developed using mixing-length theory and are compared to wind speed observations up to 300 m at the National Test Station for Wind Turbines at Høvsøre, Denmark. The measurements are performed within a wide range of atmospheric stability conditions, which allows a comparison of the models with the average wind profile computed in seven stability classes, showing a better agreement than compared to the traditional surface-layer wind profile. The wind profile is measured by combining cup anemometer and lidar observations, showing good agreement at the overlapping heights. The height of the boundary layer, a parameter required for the wind profile models, is estimated under neutral and stable conditions using surface-layer turbulence measurements, and under unstable conditions based on the aerosol backscatter profile from ceilometer observations.     

斜压性与非线性Ekman抽吸的动力特征

本文利用Ekman动量近似研究了斜压性对Ekman层动力学的影响,得到了一些新的结果。大气斜压性对Ekman层的水平风速分布及近地面的风速矢的水平分量夹角有重要的改变作用。斜压边界层顶部的非线性Ekman抽吸(垂直运动)由三个不同的物理因子决定,第一、正压性的地面地转涡度,第二、斜压性作用产生的热成风涡度,第三、正压性的地面地转涡度与斜压性的热成风涡度的非线性相互作用。这些理论结果为边界层的参数化及数值模拟结果的解释提供物理基础。     

测风激光雷达与风廓线雷达的探测性能评估及数据融合

测风激光雷达和风廓线雷达作为L波段探空测风的有效补充,均可以提供高时空分辨率的大气风场信息,然而由于工作原理和适用条件存在明显差异,在探测性能上各有优缺点,单一设备的探测数据已不能满足精细化预报的要求。本研究使用2020年1—5月北京南郊观象台的L波段探空资料对同址观测的测风激光雷达和风廓线雷达进行了数据质量评估,结果表明测风激光雷达与探空的一致性较高,U、V分量的相关系数分别为0.97和0.98,均方根误差分别为1.1和0.95 m·s-1,然而在2 km以上数据获取率较低且偏差较大;风廓线雷达与探空相比,U、V分量的相关系数分别为0.94和0.93,均方根误差分别为2.94和2.91 m·s-1,风廓线雷达的探测距离虽然更远,但在0.5 km以下和6 km以上的测量偏差较大。考虑到两种测风雷达在不同探测高度上的性能优缺点,提出分段曲面拟合法对两者的水平风资料进行融合处理,并选取个例对融合效果进行验证,结果表明,融合后的风廓线与融合前相比,风向和风速的一致性均得到明显提升。     

Conditions for freezing precipitation at some airports of Russia and the CIS: IV. Airport of Nizhni Novgorod

Results of study of conditions for freezing precipitation (FP) at the airport of Nizhni Novgorod based on 20-year series of surface observations are described. The cloud tops are estimated from radiosonde data. It is found that the monthly mean FP frequency does not exceed 0.44%; the phenomenon occurs from October to February. Over 20 years, a total of 113 FP episodes were observed, or less than six episodes annually. Freezing precipitation is more frequent at night and in the morning and very rare in the afternoon, at surface air temperatures not exceeding 0°C and not below ?10°C; in half of the cases, the air temperature is within ?0.1 to ?2.0°C. Surface wind is most frequently from south or southwest, while in the lower 4-km layer, according to the radiosonde data, wind direction mostly veers with height from south to west and north. In the boundary layer, FP is often associated with low-level jet streams, most frequently of southwest direction in the cloudy layers. The warm layers within and below the clouds occur in more than 20% of the cases. The most typical precipitation is FP from “all cold” clouds. Using objective criteria of the fronts, synoptic situations, advection, and baroclinicity, it is shown that almost all cases of freezing rain are observed in frontal zones, while freezing drizzle is as frequent at the fronts as under airmass conditions. Both types of FP are associated mainly with high baroclinicity and warm advection. The results can be used to develop an objective method of FP forecasting.