Establishment of a multiple-Doppler radar wind retrieval system and its application to the analysis of mesoscale convective systems

A multiple-Doppler radar wind retrieval system is established by using a three dimensional variation method. The system consists of two parts. One is to interpolate reflectivities and radial velocities of nine Doppler radars of the Korea Meteorological Administration (KMA) into one analysis domain. The other is to retrieve three dimensional winds by minimizing a cost function that includes the following costs and constraints: the observed radial velocity cost, background wind cost, continuity constraint and smoothness constraint. In order to verify the performance of the system, retrieved winds are compared with observed winds obtained from five wind profilers of KMA. The performance of the system depends on the relative position to the baselines between Doppler radars. However, the performance of the system is enhanced when the number of overlaps among the radial velocities increases. The system is applied to the analysis of the evolution of a mesoscale convective system (MCS) on the Changma front on 1 July 2005. The analysis result shows that a new convective cell is developed by the convergence of the low troposphere winds at the organizing stage. The analysis of the vertical vorticity reveals that, among the two vorticity generation terms to be calculated utilizing the retrieved winds, tilting or twisting source dominates the divergence source in most convective regions. The strong downdrafts associated with the storm are produced on the downdraft branch of a meridional direction secondary circulation across the Changma front.     

陕西多普勒天气雷达监测信息发布系统的开发与应用

为了充分发挥西安多普勒天气雷达在服务经济建设和防汛减灾工作中的作用 ,使市、县气象局能够方便及时地获取和使用雷达信息 ,在省气象局的组织下 ,由省、市、县三级业务技术人员合作开发了统一的、面向市县级气象局等低端用户的多普勒天气雷达监测信息系统 ,投入使用后收到了良好的效果。1　系统结构分析与传统的 71 1、 71 3等天气雷达相比 ,多普勒天气雷达有非常丰富的监测输出产品。从产品的要素类型来看 ,有基本反射率、平均径向风速和速度谱宽三种基本要素 ,以及大量的二次计算产品。从观测时间密度上来看 ,每隔 6min一次梯扫 ,2 4 h…     

Statistical evaluation of a radar rainfall system for sewer system management

Urban areas are faced with mounting demands for managing waste and stormwater for a cleaner environment. Rainfall information is a critical component in efficient management of urban drainage systems. A major water quality impact affecting receiving waterbodies is the discharge of untreated waste and stormwater during precipitation, termed wet weather flow. Elimination or reduction of wet weather flow in metropolitan sewer districts is a major goal of environmental protection agencies and often requires considerable capital improvements. Design of these improvements requires accurate rainfall data in conjunction with monitored wastewater flow data. Characterizing the hydrologic/hydraulic performance of the sewer using distant rain gauges can cause oversizing and wasted expenditures. Advanced technology has improved our ability to measure accurately rainfall over large areas. Weather radar, when combined with rain gauge measurements, provides detailed information concerning rainfall intensities over specific watersheds. Knowing how much rain fell over contributing areas during specific periods aids in characterizing inflow and infiltration to sanitary and combined sewers, calibration of sewer system models, and in operation of predictive real-time control measures. Described herein is the design of a system for managing rainfall information for sewer system management, along with statistical analysis of 60 events from a large metropolitan sewer district. Analysis of the lower quartile rainfall events indicates that the expected average difference is 25.61%. Upper quartile rainfall events have an expected average difference of 17.25%. Rain gauge and radar accumulations are compared and evaluated in relation to specific needs of an urban application. Overall, the events analyzed agree to within ± 8% based on the median average difference between gauge and radar.     

系留气艇探测风速的误差订正及其应用评估

使用系留气艇探空系统在常州、苏州、南京市区对边界层风速、温度、湿度廓线进行了观测,原始数据表明探测结果存在明显的系统误差。本文主要讨论风速订正问题,分析发现风速误差与高度和风速有关,据此提出了依据高度和依据风速的两种订正方案。对比结果表明:两种方案都能有效修正系留气艇测量风速的系统误差,高度订正方案表现更好。本文还用订正后的系留气艇探测结果与苏州市气象局的风廓线雷达资料进行对比,结果显示风廓线雷达探测结果在500 m以下系统偏小。     

On the relationship of radar backscatter to wind speed and fetch

The physics of the interaction of electromagnetic waves with the ocean surface has been an active area of research for a number of years. We present here the results of satellite and aircraft experiments to investigate the ability of active microwave radars to infer surface wind speeds remotely. Data obtained from the recent National Aeronautics and Space Administration (NASA) Skylab experiment are compared with surface wind speeds measured by low-flying aircraft and ships-of-opportunity and found to give useful estimates of the oceanic wind field. We also investigate the influence of varying wave height on radar measurements of wind speed by measuring the backscattering cross-section for constant wind speed but variable wave conditions. We conclude that this effect is of little importance.     

双线偏振雷达在一次强降雹过程中的初步应用

利用北京首都国际机场C 波段双线偏振多普勒天气雷达和NECP 再分析资料,分析了北京地区2008 年6 月23 日降雹天气过程背景及双线偏振多普勒雷达产品的演变特征。通过对雷达差分反射率因子ZDR、单位差分传播相移KDP、相关系数ρHV等偏振参数的具体分析,总结出偏振雷达观测冰雹云的一些特征：雷达强度图中出现较强回波且高度较高,ZDR趋于零,ρHV、KDP比其周围数值忽然减小。此外,还分析了KDP、ρHV在辨别虚假回波和判断回波发展中的作用。上述研究对于提高双线偏振天气雷达在强对流灾害天气监测预警、防雹减灾以及航空安全等方面应用具有一定参考意义。     

Lightning and Doppler radar observations of a squall line system

A typical squall line with damaging wind and hailstones occurred on 28 April 2006 in Shandong Province, middle eastern China, and caused great economic loss. The characteristics of cloud-to-ground lightning (CG) in the squall line were studied in detail by combining the data from the ground-based CG location network, two Doppler radars and the Lightning Imaging Sensor on the TRMM satellite. Results show that positive CG flashes accounted for 54.7% of the total CG flashes. During the initial developing stage, the CG flash rate was lower than 0.5fl min^{− 1} and most of the CG flashes were positive. It increased significantly, up to 4.5fl min^{− 1}, along with the rapid development of the squall line, and the percentage of positive CG was more than 75% during this period. The CG flash rate began to decrease but the percentage of negative CG flash increased gradually and exceeded that of positive CG during the mature and dissipating stages. Positive CG flashes tended to occur on the right flank and negative ones on the left flank. Strong wind at the surface occurred in or near the regions with dense positive CG flashes. Almost all positive CG flashes occurred near the strong radar echo regions, in the front parts of the squall line. However, the negative CG flashes almost exclusively occurred in the regions with weak and uniform radar echoes. The total flash rate in the storm was very high, up to 136fl min^{− 1}, and its ratio of intracloud flashes (IC) to CG flashes was 35:1. Dense positive CG flashes corresponded to updraft regions, they did not occur in the core of the updraft, but just behind and close to the main updraft instead. The rear inflow jet, between 3 and 6 km, played an important role in the formation of the bow echo and very strong wind at surface. The CG distribution features in the squall line were obviously different from that of an ordinary MCS. The charge structure could be roughly described as an inverted charge structure.     

多普勒天气雷达及其应用

简单介绍了多普勒天气雷达探测原理及测速能力,并介绍了多普勒天气雷达速度资料的应用。     

多普勒雷达径向散度在迎风坡降水中的应用

以太行山东部3次迎风坡降水过程为例,分析了由多普勒雷达原始资料计算得到的径向辐合与迎风坡降水分布的关系:迎风坡降水大值区落在临近径向的辐合大值区的弱辐合区内,且降水中心落在正径向速度开始减小的边界同NE风急流相交的位置。连续分布的径向辐合越强,降水越强。同时以2004年7月11—12日过程为例说明单站径向辐合和降水率的关系:径向辐合越强,降水越强,且径向辐合变化超前于降水率变化1h以上;径向辐合持续减弱3h以上,降水率减小,直至结束。径向散度对迎风坡区域的降水预报有很好的指示作用:综合分析区域径向辐合分布和单站径向辐合随时间的变化,可以预测迎风坡降水的落区、发展及生消。     

星载毫米波测云雷达在研究冰雪天气形成的云物理机制方面的应用潜力

从2008年1月10日起,受强冷空气和暖湿气流共同影响,中国南方大部分地区遭遇1954年以来罕见的冰冻天气,此次天气过程持续时间长、冰冻范围广、受灾程度重.文中简要介绍了毫米波雷达的探测特点及衰减特性;重点利用CloudSat 卫星上搭载的3 mm波长云廓线毫米波雷达(CPR)的探测结果分析了1月28日、2月10日南方冰雪天气形成的云物理机制,并且与C波段测雨雷达探测结果对比;结果表明:(1)毫米波雷达具有高空间分辨率,能够清楚地反映云的垂直和水平结构,且清晰地反映云中0℃层融化带的垂直特征.(2)1月28日湖南冻雨、2月10日贵州冻雨分别是"冰雪-雨-过冷雨"和"过冷云-过冷雨"两种典型的云物理机制,云内0℃层融化带的强度和厚度与近地面温度的高低是能否形成冻雨天气的关键因素.(3)毫米波雷达在冰冻天气研究中有很大的应用潜力;充分将毫米波雷达与天气测雨甫达以及其他遥感手段结合,可以取长补短、相得益彰.发展毫米波探测技术将对研究各种天气形成的微观物理机制、云物理的发展、气候变化的研究及人工影响天气等工作均有重要意义.     

风廓线雷达资料质量控制及其同化应用

为更好地同化风廓线雷达观测资料开展了相应的质量控制与同化应用研究。针对2013年5月广东地区13部风廓线雷达的观测数据,采用经验正交函数(EOF) 分析方法对其进行质量控制。相比原始观测,经过质量控制的风场提高(降低)了来自时空大(小)尺度的贡献,较好地滤除了小尺度高频脉动,也较好地保留了大尺度平均状态与局地中小尺度系统的共同影响,并且更加接近ECMWF再分析场。此外,还对质量控制后的数据进行了垂直稀疏化。分别计算了质量控制前、后风廓线雷达观测与NCEP 6 h预报场的差值,对比差值的特征发现,经过质量控制的数据的观测增量更好地满足了高斯分布与无偏假设。针对一个实际天气个例,基于GRAPES 3D-Var同化系统,分析了质量控制后的风廓线雷达资料对模式分析与预报的影响。试验表明,在循环同化过程中加入风廓线雷达资料可以更好地描述模式初始场低层风场的特征,从而对强降水的位置与强度做出更好的预报。针对2013年5月的批量试验表明,同化风廓线雷达资料使短期降水预报有明显的改善。     

多普勒天气雷达径向速度产品在预报中的应用

对江苏南京雷达站四年内降水前多普勒天气雷达径向速度回波及其VWP产品的特征进行了具体的研究。速度回波图的统计结果表明,非降水回波的辐合特征和降水的发生是相关的,对降水过程的发生具有一定的提前量,该预报提前量存在地域差异和季节差异。对VWP产品的统计分析表明,风向随高度顺转且风速随高度增大时,有利于降水系统的维持和发展;同时“ND”厚度和相对湿度在大面积层状云或混合云降水过程中呈反相关,在一定程度上反映了相对湿度的变化,且“ND”厚度的变化对降水的产生也有一定的提前量,对短时预报有指导意义。     

Percentile-based neighborhood precipitation verification and its application to a landfalling tropical storm case with radar data assimilation

The traditional threat score based on fixed thresholds for precipitation verification is sensitive to intensity forecast bias.In this study, the neighborhood precipitation threat score is modified by defining the thresholds in terms of the percentiles of overall precipitation instead of fixed threshold values. The impact of intensity forecast bias on the calculated threat score is reduced. The method is tested with the forecasts of a tropical storm that re-intensified after making landfall and caused heavy flooding. The forecasts are produced with and without radar data assimilation. The forecast with assimilation of both radial velocity and reflectivity produce precipitation patterns that better match observations but have large positive intensity bias.When using fixed thresholds, the neighborhood threat scores fail to yield high scores for forecasts that have good pattern match with observations, due to large intensity bias. In contrast, the percentile-based neighborhood method yields the highest score for the forecast with the best pattern match and the smallest position error. The percentile-based method also yields scores that are more consistent with object-based verifications, which are less sensitive to intensity bias, demonstrating the potential value of percentile-based verification.     

On cross-equatorial flow within a channel with application to the makasar strait

Two models are proposed to explain the flow in the Makasar Strait. Both models are non-linear baroclinic β-plane models. The first is frictionless and the second is frictional. It is shown that the cross-channel symmetry of the observed flow from December to July can best be explained by the frictional model. The occurrence of cross-channel asymmetric flow in August to November may be explained by the development of a mathematical singularity in the frictional model which causes the solution with cross-channel symmetry to be physically unacceptable. During these months, a reverse flow near the western boundary is predicted in agreement with observation. The frictionless model shows no such behaviour. The choice of model depends on the β-Ekman number ν/βL³.     

雷达数据综合处理系统设计简介

雷达数据综合处理系统是为雷达主站和终端用户开发设计的一套应用软件，为用户提供回波采集，图形显示，回波分析和决策服务的综合处理系统，系统功能齐全，操作简单，维护方便。     

新一代多普勒天气雷达产品及应用

黑龙江省引进的新型雷达是华东电子工程研究所最新研制的新一代大型C波段全相参脉冲多普勒天气雷达(简称3830天气雷达)。它与常规天气雷达相比，在探测手段上上了一个新台阶。它可以探测到常规天气雷达所不能探测到的云雾、弱降水等天气目标；但不能提供直接的要素预报，即使是有一部分预报产品，也还是需要在应用中不断订正。要真正发挥它的作用，还需广大预报员在分析应用中不断积累经验和开发研究。     

Assimilating surface observations in a four-dimensional variational Doppler radar data assimilation system to improve the analysis and forecast of a squall line case

This paper examines how assimilating surface observations can improve the analysis and forecast ability of a fourdimensional Variational Doppler Radar Analysis System(VDRAS).Observed surface temperature and winds are assimilated together with radar radial velocity and reflectivity into a convection-permitting model using the VDRAS four-dimensional variational(4DVAR) data assimilation system.A squall-line case observed during a field campaign is selected to investigate the performance of the technique.A single observation experiment shows that assimilating surface observations can influence the analyzed fields in both the horizontal and vertical directions.The surface-based cold pool,divergence and gust front of the squall line are all strengthened through the assimilation of the single surface observation.Three experiments—assimilating radar data only,assimilating radar data with surface data blended in a mesoscale background,and assimilating both radar and surface observations with a 4DVAR cost function—are conducted to examine the impact of the surface data assimilation.Independent surface and wind profiler observations are used for verification.The result shows that the analysis and forecast are improved when surface observations are assimilated in addition to radar observations.It is also shown that the additional surface data can help improve the analysis and forecast at low levels.Surface and low-level features of the squall line—including the surface warm inflow,cold pool,gust front,and low-level wind—are much closer to the observations after assimilating the surface data in VDRAS.     

南京风廓线雷达测量性能评估及应用初探

对2012年以来南京市江宁区边界层风廓线雷达每6 min的风场资料质量进行了评估,并对其在暴雨、大雾以及风切变等灾害性天气监测的应用进行了探讨。研究表明:南京风廓线雷达自投入使用以来,能够连续、稳定地获取边界层风场,四季的大部分资料获取率达80%以上,但是自2013年秋季—2014年春季的580~1 130 m层次出现获取率相对较低区,并在2014年春、夏季在770 m高度以下获取出现隔层不连续的现象(获取率50%)。通过对比每日两次的探空资料发现,边界层风廓线雷达探测得到的水平风速与常规探空资料观测基本一致,两者的偏差标准差基本在2.5 m·s~(-1)附近。夏季两种资料的匹配度最高,而冬季匹配度最差,其中大风事件与低匹配度事件有一定的联系,有必要进一步进行质量控制以提升资料质量。进一步利用雷达风廓线资料计算了南京地区垂直风切变事件的季节变化,发现冬半年中度以上等级的垂直风切变事件发生频率明显大于夏半年,其中冬季严重事件发生频率能达3%。     

新一代天气雷达定量降水估测集成系统

中国国家气象信息中心研制的多源融合实况分析1 km网格降水(简称为ART_1 km降水)产品可为灾害性天气监测预警、智能网格预报、智慧气象服务等提供更精细的数据支撑。选取广东省2019—2022年5—8月的20例致灾暴雨过程,利用未融合制作ART_1 km降水产品的区域站和水文站等两类独立站的降水资料,评估ART_1 km降水产品在暴雨过程中的准确性。结果表明：ART_1 km降水产品成功反映了广东省暴雨过程的降水落区、强度和变化趋势,且在珠三角、粤东东部和粤北北部表现最佳。降水越强,两类独立站的ART_1 km降水和观测降水的相关性越高,但均方根误差和平均值误差也越大。降水不分级时,全省约60%的独立站的ART_1 km降水和观测降水的相关系数≥0.8,超90%的独立站的均方根误差在[1.0, 5.0) mm范围内,超60%的独立站的平均值误差在±0.1 mm内。降水分级后,当小时降水较弱（< 5 mm）,全省大部分独立站的相关系数 < 0.5、均方根误差在[1.0, 5.0) mm范围内、平均值误差在[0.0, 0.5]mm范围内;当小时降水较强(≥20 mm),全省42%~56%的独立站的相关系数≥0.5,大部分独立站的均方根误差≥10 mm、平均值误差 < 0mm (且当小时降水≥50 mm,平均值误差 < -10 mm)。两类独立站的ART_1 km降水总体表现为低估,更多的站点观测融入制作ART_1 km降水产品,将有助于提升该产品的质量。