声波逾量衰减的估算

本文计算表明速度场湍流对逾量衰减的作用比温度场湍流的大5倍.在有限宽度声束条件下,引入有效湍流外尺度Le后,计算表明在大多数情况下逾量衰减系数难以忽略.当波束有张角时,同样的大气湍流状态下逾量衰减系数值随离声源距离增大而增大.过量衰减系数与声波波长关系近似为Ke∝λ~(-2).提供了考虑通量衰减作用的计算C_T~2的简单方法并给了几个计算实例.     

由声雷达回波反演湍流场结构系数

定量测量声雷达回波强度可以导出大气温度结构系数（Ct 2）和速度结构系数（Cv2）。文章简要回顾和评述了过去的工作，并讨论了逾量衰减、风和湍流等因素对该测量的影响。研究表明:逾量衰减主要是由速度场的不均匀性所造成。其次，风场也有不可忽视的衰减作用，在风速达10 m/s时，引起的衰减达50%以上。最后给出了改进后的声雷达方程和反演Ct2和Cv2的方法。初步的试验结果对理论的应用是支持的。     

准后向散射对单点声雷达测量温度结构系数的影响

本文从湍流大气对声波散射方程出发,推导出静止大气和有水平运动两种情况下,有限接收面积上的平均准后向散射截面公式。从而分析了影响平均准后向散射截面的因子,同时还计算讨论了不同天线口径、风速和值的平均准后向散射截面。 计算结果表明:在一般情况下,边界层内用声雷达测得的温度结构系数[C_T~2(θ)]要比理论上纯后向温度结构系数[C_T~2(180°)]大些;C_T~2(θ)与C_T~2(180°)比值以及C_T~2(θ)随高度的变化都与天线口径、风速分布和m值等密切相关。因此对用不同声雷达在不同大气条件作对比测量,得到某些不一致的现象,可给予一定的解释。     

对流边界层湍流结构系数的声雷达研究

本文叙述了在某些对流条件下,声雷达探测温度结构系数和风速结构系数(C_T~2和C_V~2)的简便方法.我们用声雷达在北京对于对流发展较好的自由对流体系作了实验,实验得到了9—10点钟时的C_T~2剖面和冬季13点钟时的C_V~2剖面.剖面结果表明,在Z≤0.7Z_i区间的C_T~2和C_V~2剖面与Kaimal等(1976)在明尼苏达(Minnesota)(陆上)的实验结果比较接近,在0.7Z_i≤Z≤Z_i区间,则我们用声雷达测量的C_T~2剖面和极大值都比Kaimal的结果大,并对两者的差别进行讨论.     

大气衰减与声雷达探测

本文计算了北京、武汉、上海和海口等四个地区月平均气候条件下声雷达回波的分子吸收衰减。结果表明，分子吸收衰减与大气环境之间的关系是非线性的，分析回波时不能忽略其衰减，但可用地面气象资料来订正。本文还计算了考虑声波衰减后，由声雷达探测得出的对流条件下的C T 2廓线，与Kaimal等实验结果更为接近，从而给出了一个求湍流衰减的近似方法。     

结合风廓线雷达的毫米波衰减特性初步研究

使用中国气象局大气探测综合试验基地35 GHz毫米波云雷达和L波段风廓线雷达2016年5月1日-7月31日在降水条件下的观测数据,根据不同观测模式下两部雷达得到的数据,计算在一定高度区间内不同下落速度的降水粒子反射率因子变化量,初步分析不同下落速度的降水粒子对毫米波衰减的影响。结果表明:在持续时间较长的层状云降水且降水粒子在雷达观测范围内均匀分布条件下,毫米波衰减与降水粒子下落速度呈近似线性关系,且毫米波经过的路径长度越长,衰减越大;毫米波在经过1110~2430 m,1110~3510 m的高度区间时,下落速度处于3.5~7.5 m·s-1之间的降水粒子对毫米波的衰减作用导致毫米波云雷达所测的等效反射率因子分别减小约1~7 dB和2~11 dB。     

基于微波链路的雷达回波衰减订正个例分析

降雨对微波的衰减作用在雷达探测和信号通信中有着不可忽略的影响。本文利用近年来出现的微波链路测量新方法,研究了利用微波链路进行天气雷达回波衰减订正的方法。微波链路可以直接获取传播路径上的总衰减,基于此建立衰减订正的约束条件,并利用前向迭代法对天气雷达回波进行逐库订正。首先从现有衰减订正的理论出发,通过确定微波链路衰减参考值、雷达衰减订正算法和衰减系数,建立基于微波链路的天气雷达衰减订正模型;搭建9.47GHz微波链路测量试验系统,对X波段雷达进行衰减订正试验。针对一次个例进行分析,与自动雨量站同步对比观测试验表明:订正后的雷达反射率因子明显高于雷达实测反射率因子;订正后雷达估测的降雨量与自动雨量站的观测差值减小;累积降雨量绝对偏差由-6.11mm减小到1.04mm,相对偏差由0.99%减小到0.17%;订正后估测的降雨强度与雨量计的相关性得以提高。该订正算法主要通过对参数的调整,使得k-Z关系更符合实际,从而提高了探测精度,验证了该方法的可行性与准确性。     

天气雷达回波衰减订正算法的研究(Ⅰ): 理论分析

根据雷达气象方程和k-Z关系，导出了雷达反射率因子积分取样观测资料衰减订正的逐库算法、逐库近似算法及稳定性判据。虽然仍不能解决衰减订正问题中固有的“不稳定”特征，但对提高订正计算效率防止过量订正溢出是有效的。     

锥球状粒子对偏振雷达电磁波的散射和衰减特性

采用积分方程法得到的均匀及非均匀锥球状冰雹对偏振雷达电磁波散射，衰减的数据结果，着重分析了粒子的尺度与形状因子对锥球状粒子的散射和衰减特性的影响。     

山回波的PIA因子在3 cm雷达波衰减订正中的应用

通过比较同一山体在晴雨两种天气条件下的回波反射率,确定在雷达与山体之间的降水赞成山体回波的路径积分衰减因子（Ｐａｔｈ－ｉｎｔｅｇｒａｔｅｄ ａｔｔｅｎｒａｔｉｏｎ ｆａｃｔｏｒ）,以此计算雷达与山体之间降水的真实反射率,从而把降水对Ｘ（３ｃｍ波长）面雷达波的衰减订正掉。     

Investigating Propagation of Short-Period Ocean Waves Into the Periphery of Arctic Pack Ice Using High-Resolution Upward-Looking Sonar

Springtime fetch in the Cape Bathurst Polynya System may present opportunities for winds to generate waves capable of propagating into the thick pack ice formed over the winter. A waves-in-ice event at a study site located on the Canadian Shelf in the southern Beaufort Sea that occurred 22–23 May 2011 is presented and analyzed for wave energy attenuation and dissipation characteristics. The event was monitored near the ice edge and, therefore, presents information on attenuation of waves from the ice edge into the pack. Waves of T?=?5?s, λ?=?37.5?m were observed up to approximately 143?m and approximately 77?m away from the ice edge during two separate observation periods of ice edge wave propagation. We estimated reflection coefficients of 53% and 52% and wave attenuation coefficients of α?=?2.4?×?10^?2?m^?1 and α?=?5.4?×?10^?2?m^?1, respectively, for the two periods. Estimated attenuation rates are an order of magnitude greater than in comparable studies and are inconsistent with previous findings of a “rollover” effect in attenuation rates for short-period waves.     

Wavy Vertical Motions in the ABL Observed by Sodar

Some characteristics of wavelike motions in the atmospheric boundary layer observed by sodar are considered. In an experiment carried out in February 1993 in Milan, Italy, Doppler sodar measurements were accompanied by in situ measurements of temperature and wind velocity vertical profiles using a tethered balloon up to 600 m. The oscillations of elevated wavy layers containing intense thermal turbulence, usually associated with temperature-inversion zones, were studied by using correlation and spectral analysis methods. The statistics of the occurrence of wavelike and temperature-inversion events are presented. The height distributions of Brunt–Vaisala frequency and wind shear and their correlation within elevated inversion layers were determined, with a strong correlation observed between the drift rate of the wavy layers and the vertical velocity measured by Doppler sodar inside these layers. Spectral analysis showed similarities regarding their frequency characteristics. The phase speed and propagation direction of waves were estimated from the time delay of the signals at three antennae to provide estimates of wavelength. Moreover, wavelengths were estimated from the intrinsic frequency obtained from sodar measurements of the Doppler vertical velocity and oscillations of wavy turbulent layers. The two wavelength estimates are in good agreement.     

Observations of Atmospheric Solitary Waves in the Urban Boundary Layer

The simultaneous operation of a three-axis Doppler sodar system in the centralurban area of Rome and two similar systems in the suburban area, forming atriangle about 20 km on each side, provided evidence of solitary-type wavesin the urban boundary layer. Three events, each lasting from a few minutes toabout 30 min, and ranging in depth from the minimum range of the sodar (39 m) to over 500 m, are reported here. Two events were recognizable onall three sodar records while the third event could be observed at the urbanlocation only. Time-height acoustic echo intensity records showed no-echoregions within the wave indicating transport of trapped recirculating air.This is typical of large amplitude solitary waves. The time series plots ofsodar-derived vertical wind velocity revealed a maximum peak-to-peakvariation of about 5 m s^-1 during periods of wave-associated disturbance.The vertical velocity is found to increase with height up to the top of the closedcirculation within the wave and decreases further above. The normalisedamplitude-wavelength relationship for the two events indicates that theobserved waves are close to a strongly nonlinear regime.     

雨区衰减对双线偏振雷达测雨的影响研究

以滴谱理论为基础，给出了双线偏振雷达各测雨式的雨区衰减订正公式和方法，并利用模拟的滴谱分布资料，分析了各波段双线偏振雷达各测雨式受雨区衰减的影响情况以及做衰减订正后的改进情况，提出了双线偏振雷达各测雨式在估测降雨中使用的建议。     

Mixing-height estimation in the convective boundary layer using sodar data

Sodar has been used for about 20 years to determine mixing height. However, estimation of the height of a convective boundary layer (CBL) that exceeds the sodar-probing range is still an unsolved question. As one possible way, it is suggested that one adapt a simple mixed-layer model to sodar observations during the morning growth period of the CBL, when its top can be clearly detected. Results are compared with other methods for CBL-height estimation from sodar data that have been proposed in the literature. Finally, some prognostic aspects are discussed.     

极轨气象卫星数传链路雨衰影响

极轨气象卫星通信系统受自身特点的限制和环境影响,存在各种不可避免的干扰,其中,降雨衰减对卫星链路传输的影响尤为重要。在对我国极轨气象卫星数传链路预算原理充分分析的基础上,按照ITU-R建议,构建了相应的雨衰模型,通过对国内各个地面接收站降雨衰减情况的MATLAB仿真,逐一讨论了降雨强度、天线仰角、频率、极化倾角等影响降雨衰减特性的相关因素,得出了一些有益结论,为极轨气象卫星数传链路和地面接收系统的设计提供有益参考。     

Radar and sodar probing of waves and turbulence in statically stable clear-air layers

This paper reviews the remote sensing of waves and turbulence in statically stable atmospheric layers, utilizing sodar and microwave radar echoes from the small-scale inhomogeneities in gaseous refractive index caused by localized fluctuations in temperature, humidity, and velocity. Scattering theory and sounding methodology are reviewed briefly, and the relative performance of typical radar and sodar systems compared. The main section of the paper takes the form of a summary and discussion of experimental progress since 1969, showing how the echo patterns obtained may be applied to the interpretation of multiple layering, gravity waves, internal fronts and the details of dynamic instability and the genesis of turbulence in stably stratified shear layers. In addition, methods for the measurement of the intensity of the small-scale ( /2) variability of wind, temperature and water vapor from the observed radar or sodar echo intensities, and the use of Doppler techniques for the measurement of mean velocity and turbulence are discussed.SODAR from SOund Detection And Ranging in analogy to RAdio Detection And Ranging.     

The CRPE minisodar: Applications in micrometeorology and in physics of precipitations

The technical characteristics of the CRPE minisodar are described and it is compared with the classical Doppler sodar.The results of surface layer analysis are given and simple methods are demonstrated for estimating the sensible heat flux and friction velocity in the surface layer.The system is shown to be feasible for working on the birth of gravity waves and the analysis of wind profile and turbulence evolution.Hydrometeorological studies with the minisodar are discussed with special emphasis on the problem of the relationship between wind shear in the surface layer and hydrometeor fall speed.In the conclusion, the prospective uses of the minisodar are presented.     

Study of Different Attenuation Correction Methods in Association with Rainfall Estimation for X-Band Polarimetric Radars

Different attenuation correction methods for the X-band dual linear polarimetric radar are analyzed in this paper.The specific differential phase shift K DP is always considered as an effective factor in radar signal attenuation correction.However,the values of K DP for light rains are too small,which results in unstable quality and large errors of rainfall estimation.Therefore,radar horizontal reflectivity Z H and specific differential phase shift are combined together in the Z H –K DP method to correct th...