江苏沿海“7.26”飑线大风过程诊断模拟分析

利用加密自动观测资料、EAR5 0.25°×0.25°再分析资料、常州和盐城SA天气雷达资料等和基于三维变分技术（3DVAR）的多雷达风场反演技术,并利用WRF数值模式,对2022年7月26日发生在江苏的一次大范围飑线大风过程进行了分析。结果表明：在此次飑线大风过程中,高空出流区辐散、低层低涡切变辐合,上干冷下暖湿的环境并且配合低空西南急流源源不断输送水汽,为对流的触发和组织化发展提供了较好的动力、水汽条件;飑线入海前,不稳定能量、垂直风切变、垂直上升和水汽条件均较好,而飑线入海后,众物理量配置较差,这与飑线在陆上的组织化发展、强度维持及入海后强度减弱的变化对应较好;飑线入海后,底层后侧入流减弱,使得干空气减少,不利于飑线维持,导致海上大风强度减弱。同时,纬向海陆热力差异变小使得海风的强度也逐渐减小,导致风场辐合效果变差,这可能是飑线系统入海减弱和其引发的海上大风风力变弱的原因之一,数值试验成功模拟了减小纬向热力差异会引发飑线对流系统的减弱。     

一次拖曳型飑线过程雨滴谱演变特征研究

利用Thies激光雨滴谱仪观测资料和CINRAD/SA多普勒雷达观测资料,分析了2017年7月18日一次典型中纬度拖曳型飑线过程不同发展阶段雨滴谱和积分参数的演变特征,主要结果为:1)成熟飑线回波包括对流带、过渡区和拖曳层状云区三部分,对流带前侧不断有对流带生成并合并到主对流带中,使得对流带的前沿具有强的反射率因子,并且有多个雨强大值中心。2)垂直穿过飑线对流带,雨强增加阶段有较少的小粒子(直径小于1 mm)和特大粒子(直径大于5 mm),以及较低的雨滴浓度和反射率因子,而雨强减弱阶段有较多的小粒子和特大粒子,以及较高的雨滴浓度和反射率因子;飑线加强阶段,雨滴谱有较大的峰值直径(0. 44 mm)、较多的大(直径大于3 mm)和特大粒子,而飑线减弱阶段,雨滴谱有较小的峰值直径(0. 19 mm)、较少的大粒子。3)对流带、过渡区和层状云降水雨滴谱的Gamma谱三参数N_0、μ、λ随雨强增大有明显的分层特征,相同雨强时,对流云和过渡区降水的三参数比层状云降水的数值大;而飑线不同发展阶段、不同降水类型的λ-μ关系具有一致性,二次多项式可以很好地拟合λ-μ关系。4)归一化雨滴谱参数N_W和D_0的分布可以用来区分对流云和层状云降水,并给出了新的分离线方程;另外,飑线在发展和减弱阶段的雨滴谱特征有明显差异,表明飑线演变过程降水形成的微物理机制发生变化,前期冷云过程有重要影响,而后期暖云过程起主导作用。     

浙江一次强飑线系统结构特征的数值研究

利用常规观测资料、自动气象站资料、NCEP再分析资料和高分辨率WRF模式,对2016年5月5日发生在浙江地区的一次强飑线过程进行模拟研究。结果表明,切变线是影响此次强飑线过程的主要天气系统,飑线发生在充沛的水汽,较弱的对流有效位能和中等强度垂直风切变大气环境下。WRF模式对此次飑线的演变过程和降水分布有较好的模拟能力。通过进一步分析模拟资料发现,雷暴高压和地面冷池是此次飑线风暴的重要边界层特征,边界层辐合线有利于飑线的发展和维持。飑线后侧对流层中层以下的强下沉气流,是造成此次雷暴大风的关键因素。     

海面上空晴空层状回波的初步分析

我们使用设置在岸边3．2cm波长的测雨雷达每天监视天气变化的同时观测到了低空中的晴空层状回波，因它仅出现在海面的上空，情况比较特殊，所以对它加强了注意。这种类型的回波与紧贴海面的另一种晴空回波出现的情况有些不同，紧贴海面的晴空回波在一定的客观条件下，基本上可以掌握其出现的规律，而这种回波只有在大气中某一时刻某个空间里具备了一定合适的条件它才会出现，所以以前称这种雷达回波为仙波、鬼波，对这种回波的观测也存在着一定的难度。     

一次冷涡背景下次天气尺度系统对强对流环境场的影响

在同一东北冷涡背景下,2016年6月12—13日山西境内连续2 d出现强对流天气,12日为分散性对流而13日为大范围强对流。基于多源资料通过对比探讨次天气尺度系统及其演变对风暴环境进而对风暴结构的影响,得出以下结论：（1）两日风暴强度和风暴结构差异显著。6月12日对流孤立分散且回波强度小于55 dBZ,而13日准线性风暴发展成尺度较大的弓形回波引发大范围强对流天气,回波强度达60 dBZ。（2）此次过程的关键影响系统为冷涡背景下的次天气尺度低涡。12日次天气尺度低压扰动开始出现,距离远而未影响山西;13日低压扰动东移发展为次天气尺度切断低涡,低涡相关的地面冷锋及850 hPa切变线触发山西上游对流。（3）12日低层水汽含量低,0~3 km垂直风切变弱,13日低涡前偏南水汽输送使低层显著增湿,叠加中层干冷空气形成不稳定层结,受低涡影响0~3 km风垂直切变增强至5.0×10^-3 s^-1,冷锋触发的对流风暴在上述环境下强烈发展并产生阵风锋,阵风锋组织风暴形成飑线,冷池与0~3 km风切变相互作用使飑线维持。（4）13日有利于飑线发展的环境要素与东北冷涡西侧的次天气尺度切断低涡系统密切相关,次天气尺度低涡是飑线形成发展的关键系统。     

W波段和Ka波段云雷达探测回波对比分析

通过分析W波段和Ka波段云雷达同时探测回波的差异,验证了W波段云雷达初样机的探测性能。结果表明:1)W波段云雷达初样机工作稳定,两个波段雷达都可以探测云层、云的边界、云厚等宏观参数,也可以反映出云的精细结构及云内微物理参数的变化,回波强、速度小、谱宽大的冰晶云含有上升气流及较多过冷水。2)增强模式的W波段云雷达在近地面探测雾、霾的能力比Ka波段云雷达强;两部云雷达对云层较薄的云探测能力基本相当,对多层云、云层较厚、含水量较多的云及降水的探测,由于强衰减的作用,W波段雷达所测云厚度小、云顶低、回波强度小,并且非瑞利散射也会造成W波段雷达的回波强度降低。     

基于贝叶斯分类器的多普勒天气雷达海浪回波识别和效果检验

为了提升雷达数据质量，减少海浪回波对临近预报和数值天气预报模式的雷达数据同化的不利影响，因此需要对海浪回波进行识别和去除。识别算法主要为统计获得先验概率，分析海浪和降水回波特征分布得到似然函数，再经过贝叶斯分类器来达到识别的目的。在本次算法识别过程中65个样本数据试验的临界成功指数I_CS达到了0.692，结果表明利用贝叶斯分类器对海浪回波的识别，具有较好的识别效果，能一定程度降低海浪回波误判为降水回波的错误，提高雷达数据质量。     

全极化X波段雷达掠散射海面回波统计分布特征研究

尽管复Wishart分布已被广泛应用于SAR数据统计分析,然而该分布函数却很少被用来研究雷达海面掠散射回波时间序列的统计特征。本文通过分析IPIX雷达海面掠散射回波数据发现：大尺度海浪遮挡区的雷达回波能量很低,主要是雷达系统噪声,如果将该部分低能量回波数据剔除以后,真实海面的IPIX 雷达回波时间序列数据亦满足圆高斯分布,因此,IPIX 雷达海面回波的时间序列数据也必然满足复Wishart分布。在此,我们基于Wishart分布模型分别对全极化IPIX 雷达不同极化通道数据的海面回波时间序列数据进行了统计研究,并推导给出了不同通道数据协方差矩阵元素实部、虚部及相位差等参数的统计分布函数模型。通过与雷达测量数据比计较可见,推导所得理论统计模型与实际测量数据吻合很好。本文所得结论对进一步深入理解掠散射海面雷达回波的统计特征具有一定理论意义。     

青岛近海海面上的一种雷达回波

在青岛的近海海面上，使用设置在岸边的711雷达(图1)，发现了一种雷达回波。回波是在一定的条件和情况下出现的，在出现回波的时间里，海面上及贴近海面的大气中，除船只，浮标以及海面上的小岛屿外，不见其他异物(包括鸟、虫群等)。当时的天气晴、暖而干燥。     

一种基于快速傅里叶变换的多普勒天气雷达弱杂波识别方法

多普勒天气雷达探测时常会出现电磁干扰和超折射等杂波干扰问题,通过对弱径向干扰回波的规律性特征分析,提出了一种基于快速傅里叶变换的多普勒天气雷达干扰回波识别算法,并成功应用于多普勒天气雷达径向干扰回波的识别中。研究表明,一些干扰回波具有明显的空间周期性规律,对反射率因子进行快速傅里叶变换,得到的频域上能量分布具有与常规回波明显的差异。依靠这些差异可以较好地对一些弱的干扰回波进行识别并剔除。该方法对径向上离散分布的干扰回波均有较好的识别能力,但对相对均匀和密实的径向干扰回波识别能力较弱。     

黄河三角洲*暴雨雷达回波特征及临近预报

本文利用1994－1998年东营站713数字化雷达回波资料结合高空、地面形势，对发生在黄河三角洲地区的33个暴雨日41个暴雨中尺度雷达回波系统特征及形成过程进行了总结，提出了暴雨临近预报的着眼点。在1999年的预报服务中，取得了良好的经济效益和社会效益。     

"莫拉克"强热带风暴暴雨分析

本文利用天气学分析、物理量诊断、卫星云图及雷达回波分析等方法对0309号强热带风暴“莫拉克”(MORAKOT)暴雨过程进行分析研究。结果表明，在这次暴雨过程中，西南季风的发展和冷空气的侵入作用十分突出，二者共同作用，造成热带风暴“莫拉克”外围云系的增幅发展，从而促进暴雨的发生发展。850hPa较大的正涡度、700hPa较明显的垂直上升运动、以及热带低压东南侧较大的压能梯度都对暴雨的形成和发展起到一定作用。卫星云图、雷达回波图上也比较清楚地揭示这次暴雨形成和发展的演变过程。     

Initial Examination of AltiKa's Individual Echoes

The AltiKa altimeter records the reflection of K_a-band radar pulses from the Earth's surface, with the commonly used waveform product involving the summation of 96 returns to provide average echoes at 40 Hz. Occasionally there are one-second recordings of the complex individual echoes (IEs), which facilitate the evaluation of on-board processing and offer the potential for new processing strategies. Our investigation of these IEs over the ocean confirms the on-board operations, whilst noting that data quantization limits the accuracy in the thermal noise region. By constructing average waveforms from 32 IEs at a time, and applying an innovative subwaveform retracker, we demonstrate that accurate height and wave height information can be retrieved from very short sections of data. Early exploration of the complex echoes reveals structure in the phase information similar to that noted for Envisat's IEs.     

High resolution polarimetric radar scattering measurements of lowgrazing angle sea clutter

This paper presents fully polarimetric radar scattering measurements of low grazing angle sea clutter. The measurements were obtained at a three degree grazing angle using a high range resolution (1.5 m) X-Band polarimetric radar operated from a shore site overlooking the Chesapeake Bay. The radar employs pulse-to-pulse switching between orthogonal transmitted polarizations and simultaneously measures two orthogonally polarized components of the backscattered wave to obtain full polarimetric information about the scattering process. The complete Stokes matrix, computed by averaging successive realizations of the polarization scattering matrix, is used to obtain polarization signatures and to determine the polarization dependence of the clutter. Sea spike echoes are shown to be weakly polarized and to exhibit polarization signatures indicative of multiple independent scattering mechanisms. Clutter echoes in the absence of sea spikes are shown to be highly polarized and to exhibit polarization signatures indicative of a single dominant scattering mechanism     

Real-time sea-state surveillance with Skywave Radar

To extract sea-state information from the ionospherically distorted echoes received by a skywave radar, we use a signal-processing strategy that permits real-time decisions about the quality of incoming data. This paper explains the need for an on-line processor and describes some of its engineering details. We use an array processor to quickly compute all the spectra required to display ocean waveheight, as well as some indices of data quality, while the radar interrogates an ocean cell. The results are shown in a test using an experimental radar that mapped waveheight over its North Pacific coverage area. Coverage efficiency was 85 percent, and the radar's waveheight estimates averaged 2ft(0.6 m) higher than those forecast by a numerical model.     

Phase Corrections of Small-Loop HF Radar System Receive Arrays With Ships of Opportunity

This paper is an extension of other work that addresses the use of radar echoes from ships of opportunity to determine the proper phase corrections for small-loop phased-array antennas used within high-frequency (HF) ground-wave radar systems. This technique also yields estimates for unknown ship bearings that (for cases where there is adequate signal-to-noise ratio of 20 dB or more) are consistent to within 2deg-3deg among measurements from independent radar frequencies. Within this paper, phase corrections gathered from actual ships of opportunity are compared to phase corrections gathered during a calibrated transponder run, in which the ship bearing is known. The phase corrections derived from the ship of opportunity presented in this paper were consistent with the known phase corrections to within 13.2deg (for the worst case). Furthermore, the estimates of the ship bearings collected from the two usable radar frequencies were consistent to within 1deg of each other     

Experimental investigation of fluctuations of radar signals caused by surface waves

On the oceanographic platform of the Marine Hydrophysical Institute of the Ukrainian National Academy of Sciences, we performedin situ investigations of surface waves based on the analysis of the fluctuations of radar signals at a wavelength of 1.2 cm. We analyzed both the traditional modulation transfer function used to describe variations of the scattering cross section for the scales of surface waves and the correlation of mean variations of the level of radar signals with the group structure of waving. This is of interest for applications in medium-resolution radar systems (−200–500m) recording the group structure of waving in the process of its smoothing. The experimental estimations of the amplitude of variations of radar signals caused by the group structure of waving are in good agreement with numerical results obtained with the help of a two-scale model of scattering of radar signals by the sea surface. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

Polarization Signature of Radar Backscattering Spatial Variations

A new type of polarization signatures for the radar imaging of the Earth’s cover is proposed. These signatures allow determining the degree of spatial variations of the backscattering coefficient based on the fractal approach. The azimuthal dependence of the radar backscattering spatial variations is discovered when analyzing backscattering on a pine forest.