A Model Study of Three-Dimensional Wind Field Analysis from Dual-Doppler Radar Data

A three-dimensional wind field analysis sollware based on the Beigng-Gucheng dual-Doppler weather radar system has been built, and evaluated by using the numerical cloud model producing storm flow and hydrometeor fields. The effects of observation noise and the spatial distribution of wind field analysis error are also investigated.

WIND SHEAR IDENTIFICATION WITH THE RETRIEVED WIND OF DOPPLER WEATHER RADAR

Wind shear reflects that the wind field is not uniform, which is one of the primary factors which make the retrieval of the wind field difficult. Based on volume velocity process(VVP) wind field retrieval technique, the intensity of wind shear is identified in this paper. After analyzing the traditional techniques that rely on the difference of radial velocity to identify wind shear, a fixed difference among radial velocities that may cause false identification in a uniform wind field was found. Because of the non-uniformity in wind shear areas, the difference of retrieved results between surrounding analysis volumes can be used as a measurement to show how strong the wind shear is. According to the analysis of a severe convective weather process that occurred in Guangzhou, it can be found that the areas of wind shear appeared with the strength significantly larger than in other regions and the magnitude generally larger than4.5 m/(s·km). Besides, by comparing the variation of wind shear strength during the convection, it can be found that new cells will be more likely to generate when the strength is above 3.0 m/(s·km). Therefore, the analysis of strong wind shear's movement and development is helpful to forecasting severe convections.

QUALITY CONTROL OF SINGLE DOPPLER RADAR DATA AND RETRIEVAL OF HORIZONTAL WIND FOR A LANDING TYPHOON

The removal of noise and velocity ambiguity and retrieval and verification of horizontal wind field is a prerequisite to make the best and fullest use of Doppler radar measurements. This approach was applied to the Doppler radar data collected during August 2005 for a landing typhoon Matsa (0509) in Yantai, Shangdong Province, and the verified result shows that the quality control for this dataset was successful. The horizontal wind field was retrieved and then verified by studying the characteristics of the radar radial velocity and large-scale wind field and the vertical cross section of the radial velocity determined with the typhoon center as the circle center and comparing it with satellite imagery. The results show that the meso- and small-scale systems in Matsa and its horizontal and vertical structure could be clearly retrieved using the dataset collected by single Doppler radar, and a shear or a convergence was corresponding with a band of severe storm around Matsa. At the same time, the retrieved wind field from single Doppler radar is proved to be a reliable and high-resolution dataset in analyzing the inner meso-scale structure of Matsa. It is also proved that the method for removing the velocity ambiguity could be an effective approach for preliminary quality control of the Doppler radar data, and the VAP method could also be a reasonable solution for the analysis of mesoscale wind field.

STRUCTURE OF MESO-β AND –γ-SCALE ON SOUTH CHINA HEAVY RAINFALL ON 12～13 JUNE 2005 USING DUAL-DOPPLER RADAR

The three-dimensional wind fields of the heavy rain on 12-13 June 2005 in Guangdong province are retrieved and studied with the volume scan data of the dual-Doppler radar located in the cities of Meizhou and Shantou. It is shown that the meso-β-scale and meso-γ-scale convergence lines located in the convective system at the low and middle layer play an important role in the heavy rainfall. The convergence line is the initiating and maintaining mechanism of the rain. A three dimensional kinematic structure model is also given.

Kinematic Features of a Bow Echo in Southern China Observed with Doppler Radar

A bow echo is a type of mesoscale convective phenomenon that often induces extreme weather and appears with strong reflectivity on radar images. A strong bow echo that developed from a supercell was observed over Foshan City in southern China on 17 April 2011. The intense gusty winds and showers caused huge losses of property and severely affected human lives. This paper presents an analysis of this strong meso- n-scale convective system based on Doppler radar observations. The isolated bow echo exhibited a horizontal scale of about 80 km in terms of reflectivity above 40 dBZ, and a life span of 8 hours. The system originated from the merging of a couple of weakly organized cells in a shear line, and developed into an arch shape as it moved through the shear zone. Sufficient surface moisture supply ensured the convective instability and development of the bow echo. The low-altitude winds retrieved from single Doppler radar observations showed an obvious rear-inflow jet along the notch area. Different from the conventional definition, no book- end anticyclone was observed throughout the life cycle. Very strong slantwise updrafts and downdrafts were recognizable from the retrieved winds, even though the spatial scale of the bow echo was small. Strong winds and induced damage on the surface are considered to have been caused by the mid-level rear-inflow jet and intense convective downdrafts.

ERROR COMPARISON OF WIND FIELD RETRIEVAL FROM SINGLE AND DUAL-DOPPLER RADAR OBSERVATIONS

The error distributions of the wind fields retrieved from single and dual-Doppler radar observations are given in this paper.The results indicate that the error of dual-Doppler retrieval depends on the position in the scan region of the dual-Doppler radar.The error of single-Doppler retrieval by using velocity azimuth processing(VAP)technique de- pends on the angle between the directions of wind and the radar beam.Generally,the winds retrieved from single Doppl- er radar are close to those retrieved from dual-Doppler radar.But,the error distribution of the single-Doppler retrieval is different from the dual-Doppler retrieval.We simulate the retrievals of single Doppler observation by the use of the output wind data from a 3-D numerical model of severe convection.The comparison of the simulated single-and dual-Doppler retrievals shows that the VAP may be a suitable technique for the operational analysis of mesoscale wind fields.It can also be used as a supplement to wind field retrieval in the field experiment.

GNSS海洋反射信号接收机设计与分析

针对全球导航定位系统(global navigation satellite system,GNSS)海洋反射信号遥感技术的需求,文章设计了一种GNSS海洋反射信号接收机,用以对GNSS直射信号和反射信号进行接收。多普勒延迟映射结构是GNSS海洋反射信号接收机中的关键部件,采用直射信号通道闭环、反射信号通道开环的方式,反射信号通道利用直射信号通道获得的扩频码和多普勒频率,在半个C/A码片时间内进行相关积分,得到反射信号的相关峰波形。由于海面反射的GNSS信号是多个不同反射信号的集合,合成码的相关波形和直射信号不同,其位置和形状包含了海洋学参数信息,通过此相关函数波形即可解算出海面风场信息。GNSS海洋反射信号接收机技术可以为海洋环境监测、基础测绘、灾害监测等领域提供技术支持。

Numerical Research on Effects Upon Precipitation Forecast of Doppler-Radar Estimated Precipitation and Retrieved Wind Field Under Different Model Initial Schemes

On the basis of the joint estimated 1-h precipitation from Changde, Jingzhou, and Yichang Doppler radars as well as Wuhan digital radar, and the retrieved wind fields from Yichang and Jingzhou Doppler radars, a series of numerical experiments with an advanced regional η-coordinate model （AREM） under different model initial schemes, i.e., Grapes-3DVAR, Barnes objective analysis, and Barnes-3DVAR, are carried out for a torrential rain process occurring along the Yangtze River in the 24-h period from 2000 BT 22 July 2002 to investigate the effects of the Doppler-radar estimated rainfall and retrieved winds on the rainfall forecast. The main results are as follows： （1） The simulations are obviously different under three initial schemes with the same data source （the radiosounding and T213L31 analysis）. On the whole, Barnes-3DVAR, which combines the advantages of the Barnes objective analysis and the Grapes-3DVAR method, gives the best simulations： well-simulated rain band and clear mesoscale structures, as well as their location and intensity close to observations. （2） Both Barnes-3DVAR and Grapes-3DVAR schemes are able to assimilate the Doppler-radar estimated rainfall and retrieved winds, but differences in simulation results are very large, with Barnes-3DVAR＇s simulation much better than Grapes-3DVAR＇s. （3） Under Grapes- 3DVAR scheme, the simulation of 24-h rainfall is improved obviously when assimilating the Doppler-radar estimated precipitation into the model in compared with the control experiment; but it becomes a little worse when assimilating the Doppler-radar retrieved winds into the model, and it becomes worse obviously when assimilating the Doppler-radar estimated precipitation as well as retrieved winds into the model. However, the simulation is different under Barnes-3DVAR scheme. The simulation is improved to a certain degree no matter assimilating the estimated precipitation or retrieved winds, or both of them. The result is the best when assimilating both of them into the model. And （4） Barnes-3DVAR is a new and efficient initial scheme for assimilating the radar estimated rainfall and retrieved winds.

单Doppler雷达IVAP风场反演试验

单Doppler雷达风场反演技术对于扩大Doppler雷达在中尺度气象监测和预报中的应用范围具有重要的作用。通过采用“给定方位角内风场均匀假定”提出积分速度—方位处理技术IVAP(IntegratingVelocity-AzimuthProcessing),克服了VAP技术在单多普勒雷达风场反演中对Doppler速度小尺度脉动过分敏感的缺点,及VAD(Velocity-AzimuthDisplay,速度-方位显示)技术只能反演平均风矢量问题。利用2001-08-05上海特大暴雨时虹桥机场Doppler雷达速度资料进行中尺度风场反演试验。对均匀风方位角区间分别取9°,18°,45°和90°的反演结果的比较表明,采用较小的方位角区间可以反演出与这次暴雨有关的气旋式环流和中尺度辐合线。利用地面站实测风记录及风廓线数据对IVAP反演风的质量进行了评估。结果表明,反演风的风向和地面实测风的风向有很好的相关性,反演方位角区间越大,相关性越好。与20个时次同高度上风廓线仪探测的风速数据的对比表明,IVAP技术反演出的风速和它们也有很好的相关性,两者u、v分量均方误差在2m/s左右。由于IVAP技术风场反演无需事先对Doppler雷达原始的速度资料进行人为的滤波或平滑处理,所以具有较强的客观性,便于在气象雷达预报业务中应用。

由单Doppler雷达资料反演水平风场的简单共轭函数方法的改进方案

该文改进了Ｑｉｕ和Ｘｕ（１９９２）提出的由单个Ｄｏｐｐｌｅｒ雷达探测的资料反演水平风场的简单共轭（ｓｉｍｐｌｅａｄｊｏｉｎｔ）函数方法．其基本做法是将控制方程中的状态变量改用其时间距平量代替，并加入—待反演的方程误差项．利用１９８８年夏季在美国丹佛机场所作的一次下击暴流的双Ｄｏｐｐｌｅｒ雷达观测试验资料对新方法作了检验，结果表明其对反演结果的改善是显著的．

中低纬度系统相互作用过程的中尺度风场分析

以山东济南和滨州两部S波段多普勒雷达的观测数据为基础,采用直接合成的方法,反演台风“利奇马”和西风槽相遇引发极端降水过程的中尺度系统三维风场。(1)冷暖空气交汇产生的切变线长时间维持是西风槽与台风相互作用过程中产生极端降水的关键,暖空气先进后退,表现为东南气流和西北气流先后越过雷达站,垂直方向出现复合切变;(2)最强上升运动出现在对流单体回波梯度最大的区域,最大下沉运动出现在回波顶下风方,中低层回波中心均为弱风速区;(3)发展中的对流单体各层均有气旋式入流,成熟的对流单体高层出流有反气旋式出流;(4)风垂直切变是雨团降水增幅的主要影响因素,成熟期的雨团具有低质心对流单体风暴的结构形态,垂直运动达到最强。

Coherent Doppler lidar wind retrieval for a typhoon based on the genetic simulated annealing algorithm

A method of spectrum estimation based on the genetic simulated annealing(GSA)algorithm is proposed,which is applied to retrieve the three-dimensional wind field of typhoon Nangka observed by our research group.Compared to the genetic algorithm(GA),the GSA algorithm not only extends the detection range and guarantees the accuracy of retrieval results but also demonstrates a faster retrieval speed.Experimental results indicate that both the GA and GSA algorithms can enhance the detection range by 35%more than the least squares method.However,the convergence speed of the GSA algorithm is 17 times faster than that of the GA,which is more beneficial for real-time data processing.

基于风向线性变化假定的单Doppler雷达风场IVAP反演技术

IVAP和扩展VAP技术是在常用的VAD和VAP技术基础上发展起来的单Doppler雷达风场反演技术。在IVAP和扩展VAP技术基础上,进一步改进IVAP技术,将IVAP技术反演假定从局地均匀扩展到局地风速均匀、风向随方位角线性变化,进而提高IVAP技术的反演能力。使用涡旋流场试验表明,改进后的IVAP技术对于风速稳定,而风向变化的风场的反演能力有明显提高。由于改进后的IVAP技术保持了IVAP技术反演时可不对原始资料进行平滑预处理,对于小尺度扰动具有滤波作用,其应用更为广泛。

Study on the Variational Assimilation Technique for the Retrieval of Wind Fields from Doppler Radar Data

This paper introduces a variational assimilation technique for the retrieval of wind fields from Doppler radar data. The assimilated information included both the radial velocity （RV） and the movement of radar echo. In this assimilation technique, the key is transforming the movement of radar echo to a new radar measuring variable- ＂apparent velocity＂ （AV）. Thus, the information of wind is added, and the indeterminacy of recovering two-dimensional wind only by AV was overcome effectively by combining RV with AV. By means of CMA GRAPES-3Dvar and CINRAD data, some experiments were performed. The results show that the method of retrieval of wind fields is useful in obtaining the construction of the weather system.

RETRIEVAL OF HORIZONTAL WIND PERTURBATION FIELDS FROM SIMULATED SINGLE DOPPLER RADAR OBSERVATIONS

The application of the single Doppler radar dataset analysis is usually confined to the assumption that the actual wind is linearly distributed or uniform locally.Following some dynamic features of convective weather,a conceptual model of moderate complexity is constructed,wherewith a horizontal wind perturbation field is retrieved directly from the single Doppler radar measurements.The numerical experiments are based on a 3-D cloud model-generated convective cell,whose radial velocity component is taken as the radar observations that are put into the closed equations based on the conceptual model to retrieve the horizontal wind perturbation field.After the initial field is properly treated,the retrieval equation is solved in terms of the 2-D FFT technique and the sensitivity to noise is examined. Finally,contrast analysis is done of the retrieved and the cloud model output wind fields,indicating the usefulness of the approach proposed in this paper.

Mesoscale Structure of Rainstorm Retrieved from Dual-Doppler Radar Observations Using the 4DVAR Assimilation Technique

The four-dimensional variational （4DVAR） data assimilation method was applied to dual-Doppler radar data about two Meiyu rainstorms observed during CHeRES （China Heavy Rain Experiment and Study）. The purpose of this study is to examine the performance of the 4DVAR technique in retrieving rainstorm mesoscale structure and to reveal the feature of rainstorm mesoscale structure. Results demonstrated that the 4DVAR assimilation method was able to retrieve the detailed structure of wind, thermodynamics, and microphysics fields from dual-Doppler radar observations. The retrieved wind fields agreed with the dual- Doppler synthesized winds and were accurate. The distributions of the retrieved perturbation pressure, perturbation temperature, and microphysics fields were also reasonable through the examination of their physical consistency. Both of the two heavy rainfalls were caused by merging cloud processes. The wind shear and convergence lines at middle and lower levels were their primary dynamical characteristics. The convective system was often related to low-level convergence and upper-level divergence coupled with up- drafts. During its mature stage, the convective system was characterized by low pressure at lower level and high pressure at upper level, associated with warmer at middle level and colder at lower and upper levels than the environment. However, a region of cooling and high pressure occurred in the lower and middle levels compared to warming and low pressure in the upper level during its dissipating ＇.stage. The water vapor, cloud water, and rainwater corresponded to the convergence, the updraft and the intensive reflectivity, respectively.

Study on Retrieving Three-Dimensional Wind Using Simulated Dual-Doppler Radar Data in the Cartesian Space

This paper investigates a technique of retrieving three-dimensional windfields from the dual-Doppler weather radar radial wind which is based on the Cartesian space usingvariational method. This technology provides a simultaneous resolution of three wind components andsatisfies both the minimal dual-equation system and the continuity equation. The main advantage ofthis method is that it can remove the potential drawback of an iterative solution of Cartesiandual-Doppler analysis techniques which is a major demerit when one retrieves the vertical velocityusing mass continuity equation with iterative method. The data pre-processing technology andinterpolation are also studied. This work developed a three-dimensional Cressman weighting functionto process the interpolation. In order to test the capability and advantage of this method, onenumerical experiment based on simulating dual-Doppler radar observations is designed. Firstly, wesynthesize the dual-Doppler radar radial velocity and reflectivity from the numerical model. Then,the three-dimensional wind components are retrieved from the radial velocity and reflectivity usingthis technique. The retrieved three-dimensional wind fields are found to be quite consisted withthose previously simulated wind fields. Mean difference, root-mean-square error, and relativedeviation are defined to test the precision of the method. These statistic errors reveal theaccuracy and the advantage of this method. The numerical experiment has definitely testified thatthis technique can be used to retrieve the three-dimensional wind fields from the radial velocityand reflectivity detected by the real dual-Doppler weather radar.

利用双偏振参量估计降水粒子下落末速度及三维风场反演的应用

降水系统三维风场反演的关键问题之一是准确地估算降水粒子下落末速度(W_(t)),为了探究双偏振雷达估计W_(t)的能力,利用广东省龙门地区的雨滴谱数据,建立了W_(t)与S和X波段双偏振雷达观测量的关系,并且将其应用于广州和韶关两部雷达的风场反演。对华南地区2019年4月发生的一次飑线过程进行风场反演试验,分析讨论了此次飑线过程的风场结构配置,并探索了利用不同方法估算的W_(t)在反演出的风场结构上的差异。结果表明:S和X波段雷达通过回波强度(Z H)和差分反射率(Z DR)估算W_(t),其函数形式为幂函数和一次函数,通过Z DR估算的W_(t)均方根误差相较利用Z H估算的W_(t)均方根误差更小、相关系数更大,因此通过Z DR估算的W_(t)的效果更好。此次飑线过程主要从西北向东南方向发展,风场主要是西风和西南风,在飑线前部弓状回波区域内存在明显的辐合区,垂直结构是低层辐合、高层辐散。对比利用不同方法估算W_(t)得到的三维风场,其水平风场变化主要集中在±1 m·s^(-1)的范围,水平经向风速的变化(Δu)主要是正值,水平纬向风速的变化(Δv)主要是负值,垂直方向上风速的变化(Δw)集中在±0.15 m·s^(-1)内,主要是正值,低层Δu、Δv、Δw较高层小。研究结果为降水系统三维风场反演及垂直速度反演提供了参考依据。

双多普勒雷达观测在一次雹云结构中的应用

利用常州站和泰州站双多普勒天气雷达探测数据,结合常规观测资料和ERA5再分析资料,综合分析了2019年7月6日一次强对流天气过程的天气形势、雷达回波强度演变特征和双多普勒雷达反演的三维流场信息。重点利用双多普勒雷达径向速度资料反演出格点流场,并结合回波特征分析雹云的结构。结果表明:强对流天气过程中,江苏受高空冷涡影响,在高空冷槽、高空急流、低层切变线和地面辐合线的配置条件下,形成了上干冷、下暖湿的层结不稳定结构。本次过程中,雹云不仅具有典型的强对流单体雷达回波特征,在中层强回波中心处,还有明显的“S”型水平流场结构。雹云的低层,是明显的辐合与旋转配置的水平流场。深厚的零线结构是成雹的典型特征。

2022年3月14日江西及周边地区冰雹回波特征分析

为更好地开展对江西冰雹天气的监测预警工作,使用MICAPS数据、自动站数据、雷达拼图数据、雷达PUP产品数据、双多普勒雷达反演风场数据、冰雹灾情照片视频和微信冰雹信息反馈等资料,采用天气学、雷达气象学等原理与方法,对2022年3月14日江西及周边省份冰雹回波特征进行分析,结果表明:3月14日,江西及周边省份多地出现冰雹,20个区域站出现≥17.2 m·s^(-1)的大风,24个区域站出现≥50.0 mm的降水,且雷暴大风和冷空气大风混合出现。200 hPa高空出流区、500 hPa南支槽和风速切变、850 hPa低涡和切变线、地面辐合线和西南倒槽是冰雹天气主要系统;南昌订正后较大的CAPE、较强逆温层、中层干区和低层湿区为冰雹天气发生提供了环境条件。冰雹以超级单体回波为主,有时孤立存在,有时存在于回波群、回波带之中;回波强度≥60 dBz,强回波面积最小≥18 km^(2),最大≥180 km^(2);30~60 dBz强回波梯度距离≤6 km,具有明显的云砧前伸回波;冰雹回波生命史多数在2 h以上。在冰雹回波识别中,垂直积分液态水含量(VIL)是一个很重要的特征。江西冰雹单部雷达VIL在35~60 kg·m^(-2),雷达拼图上VIL为35~50 kg·m^(-2)。在冰雹回波2.5 km CAPPI图上,冰雹回波强度均≥60 dBz,最大可达65 dBz;在双多普勒雷达反演风场上多数回波中心具有中涡旋结构、侧面辐合风场、南北风场辐合等特征;有些个例风场比较凌乱。上述分析结果为江西冰雹天气的监测预警提供了分析依据。