ANALYSIS OF CLOUD-TO-GROUND LIGHTNING CHARACTERISTICS IN MESOSCALE STORM IN BELIING AREA

The research indicates that there is a positive correlation between the negative CG flash rate and the area of radarecho with its reflectivity being equal to or greater than 30 dBz in the mesoscale convective system in Beijing area.A max-imum of the positive CG flash rate exists at both the initial and the dissipating stages.The CG flashes are usually locatednear but not within the high reflectivity center.The negative flashes are associated with.the positions of the updraft re-gion,and with the regions of wind convergence and wind shear.Generally,the negative CG flashes are concentrative andthe positive ones are dispersive.     

OBSERVATION AND MODEL ANALYSES OF POSITIVE CLOUD-TO-GROUND LIGHTNING IN MESOSCALE CONVECTIVE SYSTEMS

The analyses of spatial and temporal characteristics of positive cloud-to-ground(CG)lightning for four mesoscaleconvective systems and two severe local convective systems in 1989 and 1990 show that positive CG flash rate usuallyhas two peak values.The major peak occurs during the developing stage of the storm and most of the positive CGflashes originate at the lower part of the storm.The minor occurs during the dissipative stage of the storm and most ofthe positive CG flashes originate at the upper part of the storm,especially in the region of the wind divergence in thestorm anvil.The positive CG flash rate is almost an order of magnitude larger in the developing stage than in thedissipative stage.The appearing time of the peak of negative CG flash rate is in accordance with that of the valley of pos-itive CG flash rate.The higher the intensity of the radar echo,the higher the positive CG flash rate.Most of the positive CG flashes oc-cur when the weak echo area is larger,and mostly originate in the region where the radar echo intensity is about 10dBzand in the back region of the moving storms.The spatial distribution of the positive CG flashes is much more dispersivethan that of the negative.The mesoscale analysis reveals a bipolar lightning pattern.The mean bipole--length reaches itsminimum during the mature stage of the storm and reaches the maximum during the developing stage of the storm.The vertical distribution of the charge density is calculated by a one-dimensional charging model.Then,we discussthe producing condition of the positive CG lightning and forming cause of charge structure mentioned above.     

OBSERVATION AND MODEL ANALYSES OF POSITIVE CLOUD-TO-GROUND LIGHTNING IN MESOSCALE CONVECTIVE SYSTEMS*

The analyses of spatial and temporal characteristics of positive cloud-to-ground(CG) lightning for four mesoscale convective systems and two severe local convective systems in 1989 and 1990 show that positive CG flash rate usually has two peak values.The major peak occurs during the developing stage of the storm and most of the positive CG flashes originate at the lower part of the storm.The minor occurs during the dissipative stage of the storm and most of the positive CG flashes originate at the upper part of the storm,especially in the region of the wind divergence in the storm anvil.The positive CG flash rate is almost an order of magnitude larger in the developing stage than in the dissipative stage.The appearing time of the peak of negative CG flash rate is in accordance with that of the valley of positive CG flash rate.The higher the intensity of the radar echo,the higher the positive CG flash rate.Most of the positive CG flashes occur when the weak echo area is larger,and mostly originate in the region where the radar echo intensity is about 10dBz and in the back region of the moving storms.The spatial distribution of the positive CG flashes is much more dispersive than that of the negative.The mesoscale analysis reveals a bipolar lightning pattern.The mean bipole-length reaches its minimum during the mature stage of the storm and reaches the maximum during the developing stage of the storm.The vertical distribution of the charge density is calculated by a one-dimensional charging model.Then,we discuss the producing condition of the positive CG lightning and forming cause of charge structure mentioned above.     

低纬高原一次飑线过程的地闪演变特征分析

利用雷电定位资料、多普勒雷达资料和FY-2E红外卫星资料,分析了滇西南一次典型飑线过程的地闪变化特征。结果表明,这是一次由切变线云带内的对流单体与台风外围对流单体合并形成的典型飑线过程。在飑线发展初期,负地闪占主导地位,地闪频数在波动中缓慢增加;在飑线成熟阶段,地闪频数较高,负地闪频数达到最大峰值前10～15min,正地闪出现最大峰值;在飑线减弱阶段,地闪频数急速下降,正地闪所占比例急剧增加,当正地闪所占比例超过地闪总数的8%以上时,地闪活动开始呈减弱特征。负地闪主要发生在强对流区(>40dBz),对应着径向速度场上的辐合区,密集的正地闪发生在飑线成熟阶段,对应着辐合区附近>40dBz的强回波区域,稀疏的正地闪发生在强回波外围的云砧或稳定性降水部位。在飑线整个发展阶段,-10℃,-20℃层高度上雷达回波强度的每一次跳跃变化都对应着地闪频数的跳跃发展,且-10℃和-20℃层高度上雷达回波强度总在地闪频数变化之前6～30min。负地闪集中出现在-92～-90℃和-76～-74℃的云区,而正地闪集中发生在-90～-60℃的云区。     

山东地区冰雹云的闪电活动特征

利用山东电力部门提供的雷电定位资料,对10次冰雹过程的地闪活动特征进行了分析。通过分析发现,雹暴中正地闪占总地闪的比例平均为57.39％,远高于当地正地闪比例的气候特征值13.48％。地面降雹区基本出现在正地闪密集（活跃）区或邻近区域。在雹云快速发展阶段,地闪频数存在明显的“跃增”;在减弱消散阶段,地闪频数显著减少,但正地闪比例有所提高。负地闪频数峰值的出现通常提前于降雹0～20 min,正地闪频数峰值的出现一般滞后于降雹发生时间。整个降雹阶段对应于正地闪的活跃阶段。另外,结合对卫星观测的总闪电资料分析,发现冰雹云的云闪与地闪的比值远高于一般的雷雨过程,其云闪密度也远高于雷雨过程。以上这些特征对于冰雹的识别和对冰雹的超短时预报具有指示意义。     

华北一次强对流天气系统的地闪时空演变特征分析

利用地面雷电探测网,多普勒天气雷达和常规天气资料,分析了2005年8月1日发生在山东北部的一次具有前部对流线,后部大范围层状云降水(LLTS)的典型中尺度对流系统(MCS)的闪电活动演变特征。结果表明:整个过程中负地闪占主导地位,最高频数达到260次/5min;与负地闪比较,正地闪呈现不活跃状态。负地闪主要落在>40 dBz的强回波区内部及其边缘区域,而正地闪则分布在前部云砧和后部层状云降水区内。对地闪位置与回波强度的进一步对比分析发现,45~55 dBz的回波是最有利于地闪发生的区域,回波强度低于这一区域,随着回波强度的增大,地闪活动呈递增趋势,地闪频数在50~55 dBz的回波区域内达到峰值,>55 dBz的回波区域内地闪频数明显降低。     

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.     

一次中尺度雷暴大风过程的闪电特征分析

2005年6月21日山东北部出现了一次中尺度对流系统,并伴有地面灾害性大风。作者综合闪电定位资料、雷达和卫星资料详细分析了这次中尺度对流系统的闪电活动特征,结果表明,在系统初始发展阶段地闪频数快速增加.成熟阶段地闪频数一直较高,且都在20次/5 min以上,在减弱消散阶段,正地闪比例超过负地闪。负地闪多发生在对流降水区,而正地闪则对应于稳定的层状云降水区。逐小时地闪次数峰值滞后于云顶最低温度峰值,小于-50℃的冷云覆盖面积峰值滞后于地闪次数峰值。这次地面大风主要是较强下沉气流底部外流造成的,利用WINDEX计算的地面最大风速潜势与观测的阵风值非常接近。地面大风阶段对应着剧烈的闪电活动,地闪频数的跃增略提前于地面强风发生时间,这对灾害性天气过程的监测预警具有一定的参考价值。     

Study of the total lightning activity in a hailstorm

A thunderstorm that developed over northeastern Spain on 16 June 2006 is analyzed. This severe thunderstorm produced hailstones as large as 40 mm and had a lifetime of 3 h and 30 min. Radar cross-sections show strong vertical development with cloud echo tops reaching an altitude of 13 km. The specific characteristics of the lightning activity of this storm were: (i) a large amount (81%) of negative cloud-to-ground (−CG) flashes with very low peak currents (< 10 kA in absolute value), (ii) a very large proportion of intra-cloud (IC) flashes with an IC/CG ratio reaching about 400, (iii) a large number of “short” IC flashes (with only 1-VHF source according to SAFIR detection), (iv) a large increase of the −CG flash rate and of the CG proportion near the end of the storm. The rate of −CG flashes with a low peak current were observed to evolve similarly to the rates of IC flashes. Most of them have been assumed to be IC flashes misclassified by the Spanish Lightning Detection Network (SLDN). They have been filtered as it is usually done for misclassified +CG flashes. After this filtering, CG flash rates remained very low (< 1 min^− 1) with +CG flashes sometimes dominant. All the particular lightning activity characteristics similar to those observed in the Severe Thunderstorm Electrification and Precipitation Study (STEPS) campaigns support the hypothesis that this thunderstorm could have had an inverted-polarity or complex charge structure. The maximum IC flash rate (67 min^− 1) peaked 24 min before the presence of reflectivity higher than 60 dBZ. The IC activity abruptly decreased during the period when reflectivity was dramatically increasing. The time of maximum reflectivity observed by radar was consistent with the times of reported hail at the ground.     

春季与夏季两次雷暴大气结构及地闪特征对比

利用NCEP再分析资料、探空资料、闪电定位资料和南京、常州多普勒雷达资料,通过对比分析南京2012年2月22日春季雷暴和2011年8月10日夏季雷暴两次过程,研究不同季节影响雷暴发生的大气结构以及强弱雷暴地闪特征的差异。结果表明:风矢位温(V-3θ)图揭示的大气动力热力水汽特征能够为雷暴的潜势预报提供先兆信息。两者相较而言,春季雷暴的动力抬升作用明显;夏季雷暴主要由热对流引起,对流层上层的动力抽吸作用不明显。春季弱雷暴正地闪在总地闪中所占比例较高。无论春季弱雷暴还是夏季强雷暴,地闪落点与辐合区对应关系明显,且地闪的落点也与雷达反射率因子有较好的对应关系:地闪主要分布在强回波区(大于40 d Bz)及其外围区域。但在较强雷暴云的发展阶段,地闪多发生在风暴体伸展方向的一侧,具有引导雷达回波移动的作用,夏季强雷暴地闪簇集在垂直风切变区域。     

华北一次中尺度对流系统中的闪电活动特征及其与雷暴动力过程的关系研究

利用地面地闪定位资料、多普勒天气雷达和常规气象资料, 分析了一次具有前部对流线和后部大范围层状云降水(LLTS)的典型中尺度对流系统(MCS)的闪电活动演变特征。整个MCS生命史中负地闪占主导地位, 正地闪则表现不活跃。观测得到MCS消散阶段云闪与地闪的比例为2∶1, 地闪主要分布在地面相对位温和对流不稳定能量均达到高值的区域; 负地闪主要密集地分布在大于40 dBZ的回波范围内; 正地闪则稀疏地分布在30～40 dBZ的回波范围内。在低于-40℃的温度区域内地闪分布较多, 而密集的地闪分布在温度梯度大的区域内。结合单多普勒雷达的水平风场反演, 发现地闪集中出现在气流表现为气旋性切变或水平风呈现切变的区域。该区域与MCS的强回波区相对应, 并且地闪易发生在上升气流达到最大并开始出现下沉气流的阶段。     

雷暴天气过程中降水结构与闪电活动特征个例研究

为深入分析四川雷暴天气过程中降水和闪电活动特征,运用统计与对比方法,对四川东南部一次雷暴过程中闪电活动及降水结构之间的特征进行研究。结果表明,强降水易发生在低层辐合,高层辐散的流场中,局部地区最大降水强度发生在2~5km高度。降水开始1h后,地闪频数达到最高,地闪主要以负地闪为主,正地闪不活跃。对闪电活动与亮温分布关系知,闪电活动主要发生在低于220K降水云内,闪电活动发生的区域与降水落区一致。对总闪与地闪的分布知,负地闪主要分布在总闪的外围。通过对四川雷暴过程的研究,对雷暴预报有一定的指导意义。     

雷暴闪电活动特征研究进展

从一般雷暴、灾害性雷暴和台风的闪电活动特征以及雷暴闪电尺度特征四个方面对相关研究进行梳理.一般雷暴通常具有正常极性电荷结构,云/地闪比例在3左右(中纬度地区),地闪中正地闪占比为10％左右,负地闪位置往往更集中于对流区.灾害性雷暴倾向具有活跃的云闪,低比例的地闪,易出现反极性电荷结构,正地闪比例偏高.闪电活动与灾害性天...     

一次飑线过程的闪电活动特征

结合地闪定位资料和TRMM卫星LIS观测的总闪电资料对一次飑线过程闪电活动进行分析,结果如下:这次飑线过程的正地闪超过了负地闪,占地闪的54.7%.在系统发展的初始阶段全部为正地闪;在系统的快速发展阶段地闪频数明显增大,正地闪比例很高,均在75%以上.在系统成熟至减弱阶段,地闪频数开始下降,而正地闪比例下降,负地闪的比例却越来越大,并占据支配地位.正地闪发生在线对流区(即强回波区内或附近),负地闪发生在层状云区.正地闪并不对应于主上升气流区而是紧邻上升气流区的后部.该雷暴云内闪电活动非常频繁,云地闪比例高达26.1:1.降雹和地面大风区位于正地闪密集区内,地闪频数峰值对应于地面大风阶段.     

山东地区闪电的特征分析

利用1998～2000年山东地区雷电探测网获取的云对地闪电资料，从闪电的日变化、闪电的强度、闪电密度、极性等方面研究了山东地区的雷电分布特征。结果表明，云地闪电中负闪占绝大多数；正闪的平均强度大于负闪，在闪电强度较小和较大时发生的正闪占总正闪电总数的比例相应地高于负闪；闪电的发生也有明显的日变化，总体呈双峰双谷形式；闪电的空间分布与地形有关，也与下垫面的性质有关。对部分城市市区闪电密度的统计分析表明，济宁、莱芜、滨州、泰安、济南等位于鲁中地区的城市更应加强人工防雷工作。     

北京夏季强雷暴降水回波结构与闪电特征个例分析

利用北京市气象局短时临近交互预报系统（VIPS）资料,对2008年奥运会期间两次强降水天气过程雷达回波结构及闪电时空特征进行了细致分析。结果表明,局地性强雷暴降雨天气中,降雨率峰值与闪电活动峰值关系有超前也有略滞后的情况;关于云闪和地闪出现时间,云闪一般要超前地闪5～15min;强降水回波单体中,总闪电次数的70％以上出现在大于40dBZ的强回波区,当最大回波强度大于60dBZ时,云闪出现在强回波区的概率接近90％,说明回波强度越强,云闪出现在强回波区的概率越大;对云闪与雷达回波垂直结构分析发现,强降水单体中云闪发生的高度主要在6km以上,且云闪发生频数峰值出现在8～11km高度。     

兰州周边地闪分布特征

利用2000年和2002年设在兰州的闪电定位仪资料,分析了兰州周边地区地闪的日频次变化、强度谱分布和累计百分数、日均月变化、闪电密度、极性等特征,并与山东地区的分布做了比较。结果表明,兰州周边地区的云—地闪电中负闪占绝大多数,正闪的平均强度大于负闪,正负闪的比值在午后至次日凌晨大于其均值;总地闪和负闪的日变化呈典型的双峰变化,正闪的双峰特征不明显;兰州西南偏南的渭源和陇西县是闪电频发的中心地带,闪电空间分布中心与冰雹发生源地和影响区对应一致;闪电多发区与地形和气候背景有很大关系。     

雷暴中雷电活动与WRF模式微物理和动力模拟量的对比研究

利用WRF模式模拟发生在成都地区的典型雷暴天气过程,得到相应雷电活动过程中微物理和动力输出场,将其与雷电监测定位网所探测到的地闪资料进行对比分析,在电荷分离的微物理学基础上讨论了WRF(Weather Research and Forecasting)模式输出的不同微物理及动力因子与地闪的相关性。结果表明:-10℃到-20℃之间的电荷分离区域内,冰晶粒子与霰粒子质量混合比最大值与地闪频数随时间变化趋势基本保持一致。在雷电活动中后期,霰、冰晶及雪晶粒子最大值位置与地闪密度大值中心位置对应性较好,空间上均能指示地闪发生区域。最大上升速度与风暴相对螺旋度可以指示地闪频数变化,风暴相对螺旋度空间上可指示地闪密度大值中心。模拟结果表明WRF模式微物理及动力输出场可以指示地闪活动的发生时间和位置,表现了日益成熟WRF模式进行雷电数值预报与研究的潜能。     

The characteristics of cloud-to-ground lightning activity in hailstorms over northern China

The characteristics of cloud-to-ground (CG) lightning for ten hailstorms in Shandong Province of China were analyzed statistically. It is found that the hailstorms in this study present dominant positive CG flashes during periods of falling hail. One specific hailstorm on 16 June 2006 was studied in detail using the data from a CG lightning location network, Doppler radar and cloud images. Comparison between the brightness temperature of cloud-top and CG flash locations indicated that most flashes occurred in the region with temperatures lower than − 40 °C, while dense positive CG flashes occurred in the range between − 40 °C and − 50 °C. Negative CG flashes occurred mostly in the relative weak radar echo region, and positive CG flashes were distributed in the strong echo region especially with a large gradient of echo intensity. CG flashes tended to occur in the cloud region with reflectivity between 25 dBZ and 35 dBZ. Comparison between the wind field retrieved from Doppler radar and the location of CG flashes indicated that the flashes were located in the convergent region at lower to middle levels.     

成都地区地闪时空特征分析

利用XDD03A型闪电定位仪所取得的3年资料,初步研究了成都周边地区地闪特征。地闪中正地闪占绝大多数,其平均强度为6045 A,略高于负地闪的5974 A。地闪强度基本集中在12000 A以下。地闪活动具有明显的日变化,总体呈单峰单谷形式,地闪频次在60以上的峰值时段是18:00~24:00和01:00,频次在10以下的谷值时段是10:00~13:00,夜间闪电活动明显大于日间。正地闪频次日变化趋势和总地闪相同,负地闪频次日变化趋势除一些小波动外,和正地闪、总地闪相同。正负地闪频次的月变化趋势相同,6、7、8月闪电数较多,4、5、9、10月闪电数较少。通过统计分析,发现各月地闪频次和对应的各月降水量有较好的相关性。成都周边地区地闪活动密集,6、7、8月的地闪密度大大超过4、5、9、10月。