A Case Study of Cloud-to-Ground Lightning Activities in Hailstorms under Cold Eddy Synoptic Situation

There were three hailstorms in Shandong Province,caused by a same northeast cold eddy situation on 1 June 2002.Cloud-to-ground (CG) flashes occurring in the weather event were observed by Shandong Lightning Detection Network (SLDN),which consists of 10 sensors covering all over Shandong Province.The temporal and spatial distributions of CG lightning are investigated for the three hailstorms by using the data from SLDN,Doppler radar and satellite.The results show that different thunderstorms present different lightning features even if under the same synoptic situation.The percentage of positive CG lightning is very high during the period of hail falling.CG flashes mainly occurred in the region with a cloud top brightness temperature lower than -50°C.Negative CG flashes usually clustered in the lower temperature region and tended to occur in the region with maximum temperature gradient,while the positive ones usually spread discretely.Negative CG flashes usually occurred in intense echo regions with reflectivity greater than 50 dBz,while the positive CG flashes often occurred in weak and stable echo regions (10-30 dBz) or cloud anvils,although they can be observed in strong convective regions sometimes.Almost all hail falling took place in the stage with active positive flashes,and the peak positive flash rate is a little prior to the hail events.The thunderstorm could lead to disastrous weather when positive CG lightning activities occur in cluster.Severe thunderstorms sometimes present a low flash rate at its vigorous stage,which is probably caused by the"mechanism of chargeregion lift"through investigating the reflectivity evolution.Combined with the total lightning (intracloud and CG) data obtained by LIS onboard TRMM,the phenomenon of high ratio of intracloud flash to CG flash in severe hailstorm has been discussed.The competition of the same charge sources between different lightning types can also be helpful for explaining the cause of low CG lightning activities in severe storms.     

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。     

Comparison of lightning activity and radar-retrieved microphysical properties in EULINOX storms

A combined analysis of microphysical thunderstorm properties derived by C-band polarimetric Doppler radar measurements and lightning observations from two ground-based systems are presented. Three types of storms, a multicell, a supercell, and a squall line, that were observed during the European Lightning Nitrogen Oxides project (EULINOX) are investigated. Correlations are sought between the mass of rain, graupel, hail, and snow derived form radar observations at different height levels and the electrical activity, represented either by cloud-to-ground or intracloud flashes. These relationships are explained by connecting the radar-derived properties with the non-inductive charging process. For the multicell and the supercell storm, the lightning activity can be linearly correlated to both the hydrometeor total mass and class specific mass in the upper part of the storm. It is shown that the fractions of graupel and hail above the −20 °C-level in these storms positively correlate with the intracloud flash activity in the supercell, and negatively for the cloud-to-ground lightning frequency in the multicell. No such relation can be established for the squall line, indicating that the convective organization plays a crucial role in the lightning development. The analysis of the masses in the different storms shows that lightning activity cannot be parameterized by total mass alone, other parameters have to be identified. The results provide important information for all lightning studies that rely on bulk properties of thunderstorms, e.g., the parameterization of lightning in mesoscale models or the nowcasting of lightning by radar.     

广州地区雷暴过程云-地闪特征及其环境条件

应用雷电定位系统和高空观测资料并结合雷达回波资料, 对广州地区雷暴过程云-地闪特征进行分析, 并就有、无云-地闪出现的两组不同对流天气过程的环境条件进行了比较研究。结果表明:广州地区的雷暴过程以负的云-地闪为主, 负云-地闪所占比例在90%以上。云-地闪发生频率与雷暴系统强度演变有直接联系, 对于同一系统来说, 随着系统回波强度的增强, 云-地闪发生的频率也增高。但不同系统中, 云-地闪发生频率有很大不同, 回波强(弱)的对流系统并不意味着云-地闪发生的频率就高(低)。有云-地闪记录的对流天气过程具有更大的垂直切变、更高的相对风暴螺旋度以及更多的对流抑制能量, 云-地闪现象更易于出现在更加有组织和更强的对流系统中。研究还发现广州及周边城市区域对雷暴系统回波强度及云-地闪现象可能有影响, 两个典型个例分析表明, 雷暴系统移经城市区域时回波强度减弱, 云-地闪发生频率减小, 雷暴移过城市区域后, 强度可重新加强, 云-地闪发生频率增大。     

Evaluating the impact of lightning data assimilation on mesoscale model simulations of a flash flood inducing storm

Flash floods are associated with highly localized convective storms producing heavy rainfall. Quantitative precipitation forecasting of such storms will potentially benefit from explicit representations of deep moist convection in numerical weather prediction models. However, explicit representation of moist convection is still not viable in operational mesoscale models, which rely on convective parameterizations for issuing short to medium-range forecasts. In this study we evaluate a technique that uses regional Cloud-to-Ground (CG) lightning observations to define areas of deep moist convection in thunderstorms and adjust the model-generated precipitation fields in those regions. The study focuses on a major flash flood inducing storm in central Europe (23 August 2005) that was simulated with the aid of an operational weather forecasting system (POSEIDON system based on Eta/NCEP model). The performance of the technique is assessed using as reference distributed rainfall estimates from a network of radar observations. The results indicate that CG lightning data can offer sufficient information to increase the mesoscale model skill in reproducing local convective precipitation that leads to flash floods. The model error correction is shown to be proportional to the density of lightning occurrence, making the technique potentially suitable for operational forecasting of flash flood inducing thunderstorms.     

Climatology of Lightning Activity over the Indian Seas

The climatology of lightning activity over the Indian seas (Arabian Sea (AS) and Bay of Bengal (BoB)) has been studied using monthly satellite-based lightning flash count grid (0.5°?×?0.5°) data from 1998 to 2007. These data have been used to investigate the annual and seasonal variations in lightning activity over the Indian seas. It was found that annual variations in flash rate density and sea surface temperature (SST) show a bimodal pattern with the first peak occurring in May and the second in October. The correlation coefficients between flash rate density and SSTs are 0.76 and 0.65 for the AS and BoB, respectively. Further, the relationship between flash rate density and a low pressure system (LPS) over the BoB shows that the formation of severe tropical cyclonic storms starts during April with the maximum number of storms forming during August. The performance of monsoon on a seasonal and monthly basis depends on the total number of lows, the formation of a depression in the monsoon trough, and the number of days with an LPS. Secular decreases in the number of lows and monsoon depressions were observed in 2000, 2002, and 2004. Overall, results indicate that the peaks in SST during April and September/October over the AS and the BoB may be responsible for advancing the onset of the southwest and northeast monsoon by 30–40 days.     

Lightning flash climatology in the southern great lakes region

Abstract

We have made a preliminary study of cloud‐to‐ground lightning over southern Ontario and the adjoining Great Lakes region. The lightning data set, using magnetic direction finding, is sufficiently accurate to study lightning climatology. Cloud‐to‐ground flash totals have been found for the three warm seasons 1989–91. A large variation in flash total, lightning‐day frequency and number of high flash density storms occurs over the area, with the maximum in southwestern Ontario. The area of the maximum also has a strong diurnal cycle and relatively few positive flashes. Several physical causes may contribute to this. Lake areas usually have slightly fewer flashes than nearby land areas and warm water usually has more flashes than cold water. The Great Lakes do produce more lightning than ocean areas. Convergence lines of lake breezes and other lake circulations can, however, be sites for storms with intense lightning. High surface temperature and moisture leads to an increase in lightning generation. Over land, upslope flow increases lightning‐producing storms and downslope flow decreases them. High flash density storms may be favoured by smooth rather than rough ground, and by open farmland rather than forest. On the other hand, there does not seem to be a clear urban effect increasing lightning in the Great Lakes     

基于闪电数据的雷暴识别、追踪与外推方法

该文提出了一种新的雷暴识别、追踪与外推方法。该方法基于地闪数据,利用密度极大值快速搜索聚类算法实现雷暴的识别,采用Kalman滤波算法实现雷暴的追踪与外推。应用该方法处理了2013年的全国地闪定位数据,同时利用多普勒天气雷达等数据对选取的个例进行评估。结果表明:该方法能有效识别雷暴并对其进行实时追踪,且能有效处理雷暴分裂与合并的情况;算法具有较好的0~60 min的临近外推预报能力,各项性能指标整体与TITAN (Thunderstorm Identification, Tracking, Analysis and Nowcasting) 算法接近,在30 min时效有更好的表现。该方法能够实时监测、预报全国雷暴发生发展状况,对于0~60 min临近预报具有一定参考价值。     

山东一次飑线过程的闪电特征和大风形成机制分析

利用闪电定位资料、多普勒雷达资料和卫星资料分析2016年6月13日发生在山东的一次飑线天气过程的地闪变化特征和大风形成机制,结果表明:本次过程发生在东北冷涡影响背景下,大气层结上冷下暖,随着层结不稳定性逐渐增强和不稳定能量的积蓄,在较强的深厚垂直风切变环境下触发强对流风暴进而组织成飑线。整个飑线过程中负地闪占主导地位,约占地闪总数的89.25%;在飑线的成熟阶段,负地闪频数达到最大峰值后的5～10 min,正地闪也出现最大峰值;负地闪主要出现在回波发展至成熟阶段,多发生在45 dBZ的强回波区域中;正地闪主要出现在飑线的成熟至消散阶段;当TBB达到最低值时,飑线达到最强盛阶段,地闪频数达顶峰。利用WINDEX计算的地面最大风速的潜势与观测的地面极大风速较接近;地面大风阶段对应着剧烈的闪电活动,冰雹大风等灾害性天气的最强时刻与正地闪的峰值出现时间较为一致。     

Transient currents in the global electric circuit due to cloud-to-ground and intracloud lightning

Intracloud (IC) and cloud-to-ground (CG) lightning flashes produce transient changes in the electric field (E) above a thundercloud which drive transient currents in the global electric circuit (GEC). Using in-cloud and above-cloud E data from balloons, ground-based E data, and Lightning Mapping Array data, the above-cloud charge transfers due to lightning transients are estimated for five IC and five CG flashes from four thunderstorms that occurred above the mountains in New Mexico, USA, in 1999. For the five CG flashes (which transferred − 4 to − 13 C to the ground), the transient currents moved + 1 to + 5 C of charge upward from cloudtop toward the ionosphere, with an average transient charge transfer of about 35% of the charge transferred to ground. For the five IC flashes (which neutralized 6 to 21 C inside the cloud), the transient currents moved − 0.7 to − 3 C upward, with an average transient charge transfer of about 12% of the lightning charge. Estimates for three thunderstorms indicate that the transient currents made only a small GEC contribution compared to the quasi-stationary Wilson currents because of the offsetting effects of IC and CG flashes in these storms. However, storms with extreme characteristics, such as high flash rates or predominance of one flash type, may make a significant GEC contribution via lightning transients.     

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.     

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.     

Investigations of the development of thunderstorm with hail. Part 2. Analysis of methods for the forecast and diagnosis of the electrical properties of clouds

The results of observation of the development of a high-depth thunder-hail storm is presented. The measurements were carried out with the MRL-5 weather radar and LS8000 lightning detection system. The electrical parameters of the investigated cloud obtained with LS8000 as well as their relations to radar-derived cloud characteristics and to the indirect criteria of electrical conditions computed on their basis are analyzed. The possibility to forecast thunderstorm based on different thermodynamic criteria is investigated. The high correlation was revealed between the total lightning current in the LF range and the lightning flash rate in the LF and VHF ranges. The total charge transferred by negative lightnings from this cloud to the ground is equal to 387 C; the average value of charge per one lightning is 0.44 C. Regression equations linking the radar criteria of lightnings and the lightning flash rate are presented.     

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气现象之间存在关联性,部分雹暴过程具有两次闪电活跃阶段。台风中大部分闪电发生在外雨带,眼壁/外雨带闪电爆发很可能预示气旋强度的增强以及路径的改变。由闪电持续时间、通道空间扩展所表征的闪电尺度与雷暴对流强度相关。弱对流雷暴或雷暴的弱对流区域可能由水平扩展、垂直分层的电荷分布形态主导,闪电频次低,闪电空间尺度大;强对流雷暴或雷暴的强对流区域可能由交错分布的小电荷区主导,闪电频次高,闪电尺度小。      

Anomalous lightning activity over the Metropolitan Region of São Paulo due to urban effects

A significant enhancement in the number of negative cloud-to-ground (CG) lightning and a decrease in the percentage of positive CG flashes are observed over the city of São Paulo, similar to observations in other large urban areas. Strong evidence indicates that this anomalous behavior results from several mechanisms related to the urban effect. In this paper, we investigated the importance of the air pollution using CG lightning data provided by the Brazilian lightning detection network (BrasilDAT) for a 6-year period (1999–2004). Due to the large variations in the CG lightning activity in response to different meteorological processes, it is not an easy task to infer the contribution of air pollution to the enhancement in the lightning activity. In order to overcome such difficulty, two approaches were considered: (1) the weekly variation of the number of days with lightning in comparison to the mean concentration of particulate matter (PM₁₀), as well as other thermodynamical parameters; (2) the variation of the number of CG flashes and the maximum storm flash rate per individual thunderstorm for different levels of pollution. The results of both analyses suggest that: first, the enhancement in the CG lightning activity during the week days over São Paulo metropolitan region is related to the PM₁₀ concentration (pollution); second, the PM₁₀ concentration tends to increase the lifetime of the storms and, in consequence, the number of flashes per storm, and not the flash rate of the thunderstorm; and third, the effect of the pollution in the enhancement of the CG lightning activity is probably less significant compared to the effect of the urban heat island.     

Analysis of thunderstorm and lightning activity associated with sprites observed during the EuroSprite campaigns: Two case studies

During the summers of 2003 to 2006 sprites were observed over thunderstorms in France by cameras on mountain tops in Southern France. The observations were part of a larger coordinated effort, the EuroSprite campaigns, with data collected simultaneously from other sources including the French radar network for precipitation structure, Meteosat with images of cloud top temperature and the Météorage network for detection of cloud-to-ground (CG) flash activity. In this paper two storms are analyzed, each producing 27 sprite events. Both storms were identified as Mesoscale Convective Systems (MCS) with a trailing stratiform configuration (ST) and reaching a maximum cloud area of ~ 120,000 km². Most of the sprites were produced while the stratiform area was clearly developed and during periods of substantial increase of rainfall in regions with radar reflectivity between 30 and 40 dBZ. The sprite-producing periods followed a maximum in the CG lightning activity and were characterized by a low CG flash rate with a high proportion of + CG flashes, typically around 50%. All sprites were associated with + CGs except one which was observed after a − CG as detected by the Météorage network. This − CG was estimated to have − 800 C km charge moment change. The peak current of sprite-producing + CG (SP + CG) flashes was twice the average value of + CGs and close to 60 kA with little variation between the periods of sprite activity. The SP + CG flashes were further characterized by short time intervals before a subsequent CG flash (median value < 0.5 s) and with clusters of several CG flashes which suggest that SP + CG flashes often are part of multi-CG flash processes. One case of a lightning process associated with a sprite consisted of 7 CG flashes.     

突发性强对流天气快速识别预警改进方法

传统多普勒天气雷达强对流灾害性天气监测采用固定阈值判别法给出强风暴的冰雹闪电灾害预警结果,该方法不适用于不同经纬度、季节和复杂地形条件下的强对流天气识别预警。本文利用循环递归的区域生长法对TITAN算法进行改进,从而快速识别三维强风暴单体及其雷达特征物理量;使用多普勒天气雷达和TRMM星载气象雷达的历史观测数据反演河北石家庄地区春夏两季复杂地形条件下的强风暴灾害性天气Logistics多元线性回归概率预警模型。对发生在河北石家庄夏季的一次强飑线天气和发生在春季的一次超级多单体风暴天气进行冰雹闪电灾害性天气识别预警实验,并与传统算法进行误差对比分析。实验结果表明:与传统算法对比,该方法对强风暴天气识别预警的定位精度较高,并且其漏报率和虚报率较低,有助于快速识别预警强对流灾害性天气。      

北京地区地闪活动时空分布特征

基于国家雷电定位网2010—2014年雷电定位数据和2010—2013年地面气象资料,分析了北京地区各季地闪活动时空分布特征及其与降水量的关系。结果表明,北京地区雷电活动具有明显的日变化特征;雷电发生频次随季节变化明显,负闪和全地闪在秋季变化幅度最大;雷电发生频次最大值和最小值出现时间随季节变化,春季、夏季日循环峰值出现时间在22∶00—23∶00(北京时间),秋季日循环峰值出现时间在01∶00,冬季则为15∶00且不具有显著性;从空间分布上看,可以看出雷电活动分布具有局地性特征,北京地区雷电活动最频繁的地区集中在密云县和平谷区的迎风坡一带、通州区与市辖区交界处,高雷暴日区域位于延庆县、昌平区和平谷西部,延庆县和怀柔区的北部及房山区和门头沟交界处的西部,雷暴发生频次和雷暴日空间分布不完全吻合。通过各季雷电发生频次日变化序列的谐波分析可知,日循环为日变化的主要信号。春季、夏季、秋季雷电发生频次和降水量两者整体变化趋势一致,降水量较雷电发生频次变化缓慢。     

Case studies of sprite-producing and non-sprite-producing summer thunderstorms

Three summer thunderstorms in the eastern region of China were analyzed in detail using multiple data, including Doppler radar, lightning location network, TRMM （Tropical Rainfall Measuring Mission）, MT- SAT （Multi-Function Transport Satellite） images, NCEP （National Centers for Environmental Prediction） Reanalysis, and radiosonde. Two of the three storms were sprite-producing and the other was non-sprite- producing. The two sprite-producing storms occurred on 1 2 August and 2~28 July 2007, producing 16 and one sprite, respectively. The non-sprite-producing storm occurred on 29-30 July 2007. The major ob- jective of the study was to try to find possible differences between sprite-producing and non-sprite producing storms using the multiple datasets. The results showed that the convection in the 1-2 August storm was the strongest compared with the other storms, and it produced the largest number of sprites. Precipitation ice, cloud ice and cloud water content in the convective regions in the 1-2 August storm were larger than in the other two storms, but the opposite was true in the weak convective regions. The storm microphysical prop- erties along lines through parent CG （cloud-to-ground lightning） locations showed no special characteristics related to sprites. The flash rate evolution in the 1-2 August storm provided additional confirmation that major sprite activity coincides with a rapid decrease in the negative CG flash rate. However, the evolution curve of the CG flash rate was erratic in the sprite-producing storm on 27-28 July, which was significantly different from that in the 1 2 August storm. The average positive CG peak current in sprite-producing storms was larger than that in the non-sprite-producing one.     

一次强雷暴过程的闪电特征分析

对2006年6月25日焦作地区强雷暴天气分析表明,东北低涡后部西北急流出口区与地面冷锋的耦合是造成本次过程的直接影响系统。针对该过程伴随的强烈闪电现象,通过研究卫星云图和雷达回波特征,结合XDD03A型闪电定位仪对闪电过程的重现,探索强雷暴天气形势下对流云不同部位的闪电分布以及雷暴不同生命期所对应天气现象的闪电分布特征。