云下部正电荷区与负地闪预击穿过程

三维雷电观测系统LMA(Lightning Mapping Array)是最近发展起来的基于GPS时钟同步的闪电VHF辐射源到达时间差(TOA)定位技术,能以很高的时间分辨率(50 ns)和空间定位精度(50-100 m)展现闪电放电发展过程的三维时空分布,揭示雷暴中电荷结构及其与放电过程的关系.文中利用三维雷电VHF辐射源观测资料分析了负地闪预击穿过程的时空分布特征,讨论了云下部正电荷区对负地闪发生的影响,其结果表明在首次回击之前存在长时间预击穿过程的负地闪中,预击穿过程是云中部负电荷区与下部正电荷区之间的一种云内放电过程,闪电起始于云中部负电荷区,然后向下发展传输,进入正电荷区后闪电通道在云下部正电荷区水平发展,其放电特征与反极性云闪放电一致,云内放电过程最后阶段的K型击穿激发了地闪的梯级先导,梯级先导穿过云下部正电荷区向下发展传输.云下部正电荷的存在是导致负地闪首次回击之前存在长时间云内预击穿过程的主要原因.     

Fine-resolution simulation of cloud-to-ground lightning and thundercloud charge transfer

2-D 12.5 m-resolution simulations of cloud-to-ground (CG) lightning discharge processes have been performed using an improved stochastic lightning model for different types of cloud charge distributions, such as dipole, tripole, bi-dipole and multi-layer charge structures produced from the numerical simulation of thundercloud electrification. The modelling produced the fine branched channel structure of CG lightning and the results illustrate the relations between CG lightning channel propagation and cloud charge distribution. The simulated features of CG lightning are associated with the observed results. The simulation studies are essential in our understanding of complex charge transfer processes caused by CG lightning discharges in thunderclouds. The induced charges of opposite polarity are deposited or embedded in the local volumes where the bidirectional leaders passed during a CG lightning discharge. Although the embedding affects charge structure only in a pair of significant positive and negative charge regions closest to the ground, the electric field strength acutely weakens and electrostatic energy in thunderclouds is significantly consumed when the discharge terminates. In addition to simulating the upward and downward breakdown of the initial leader to ground and the ensuing return stroke (RS), the simulation assumes that current continues to flow in the channel to ground and determines the upward breakdown until the end of the discharge. For the subsequent discharge sub-process, the upward leader channel tends to transfer the charges with the same polarity as the RS, while the downward leader channel favors transfer of opposite charge to ground. In the sub-processes of a few CG flash simulations, the magnitude of the opposite charges from the downward leader exceeds that of charges with the same polarity from the upward leader so that the net charges transferred to the ground have a reversed polarity to the RS. The simulation presents similar features of CG lightning as those observed in realistic bipolar CG lightning.     

一次暖云强降水主导的对流单体闪电活动特征

利用中国气象局雷电野外科学试验基地(CMA_FEBLS)三维闪电观测数据,结合广州双偏振雷达观测数据,分析了2017年5月7日广东一次暖云强降水对流单体的闪电活动及其与云降水结构的关系。该单体在4 h内产生1250个闪电,地闪比例约24%。绝大多数闪电出现在4~12 km高度,对应温度层为0℃至-40℃;闪电放电活动的峰值高度出现在8.5 km,对应环境温度约-19℃。分析的强降水单体宏观上呈现上正、中负、下正的三极性电荷结构,中部负电荷核心区约为-8℃至-15℃。在闪电活动区域中,由干雪粒子主导区域占比约82%,霰粒子主导区域占比约11%,且大部分与闪电活动关联的霰粒子主要位于4~8 km高度。总闪频数与30 dBZ雷达回波顶高、-20℃温度层上大于20 dBZ的回波体积具有较好的相关性。闪电活动的平均位置高度与20 dBZ雷达回波顶高和-20℃温度层上大于30 dBZ的回波体积具有较好的相关关系。闪电活动与最大降水强度之间具有较好的时序对应关系,单个闪电表征降水量的值为107 kg/fl量级。     

闪电宽带电场三维定位及其回波特征

利用自制闪电宽带电场三维定位系统, 分析了山东地区一次雷暴过程闪电三维时空结构。结果表明, 在云内击穿放电整个时间序列中, 辐射源空间分布（对应强电场区分布）呈现明显的三极性分层电荷结构, 并分布在3个高度层次： 6~8 km为上部正电荷区, 4~6 km为中部负电荷, 2.5~4 km为下部次正电荷区。云内放电首先出现在中部负电荷区, 然后产生向上发展的负流光进入上部正电荷区传输, 形成向上发展的云闪; 随着雷暴发展, 产生向下发展的负流光进入下部次正电荷区, 形成向下发展的云闪, 且能维持到雷暴发展后期。结合雷达回波分析表明, 雷达回波的强度影响着闪电活动, 强回波区的增加会使得强电场区域增加, 但是强电场区域并不与最强回波区域对应, 除下部正电荷区的底部会有部分辐射源出现在回波强度为40~50 dBz的区域中以外, 大多数的辐射源出现在25~35 dBz的中等回波区范围内, 强回波区域中通常较少出现击穿放电。     

中国南北方雷暴及人工触发闪电电特性对比分析

通过对我国南北方雷暴及人工触发闪电电特性的对比分析，发现南北方雷暴及人工触发闪是电特性有很大差异。北方雷暴电荷结构呈三极性，人工触发闪电是在地面电场为正的情况下成功的。主要由连续电流和双极性电流脉冲组成，最大放电电流为１ｋＡ，中和电葆量只有几库仑；南方雷暴则为偶极性，触发闪电由连续电流和我次回击组成，电流峰值在于１０ｋＡ。触发闪电时地面电场均为负极性，其中在４ｋＶ／ｍ以上；触发高度在北方最低为２６     

利于上行负地闪始发的电荷区参数数值模拟

在经典偶极性电荷结构下,结合已有的闪电放电参数化方案及中国气象局雷电野外科学试验基地的广州高建筑物雷电观测站(Tall-Object Lightning Observatory in Guangzhou,TOLOG)观测分析结果,不断调整主负电荷区参数进行二维高分辨率闪电模拟试验,讨论自持型上行负地闪与云中闪电之间的相互竞争关系以及有利于自持型上行负地闪始发的云中电荷结构。数值模拟结果表明:自持型上行负地闪始发与电荷结构存在一定关系,在主负电荷区越高的情况下,始发自持型上行负地闪需要的主负区电荷密度与电荷分布范围越大。对于不同类型的闪电始发条件,推测存在自持型上行负地闪始发的主负电荷区高度阈值,当主负电荷区高度高于该值时,随着主负区电荷量的不断累积,会始发起始于云中的闪电而不是自持型上行负地闪,当主负电荷区高度低于该值时,电荷的不断积累会导致自持型上行负地闪始发。     

雷暴云内电荷水平分布形式对闪电放电的影响

为了定量探究雷暴云内电荷水平分布形式对闪电类型和先导传播行为的影响,建立了典型雷暴云电荷结构模型,引入控制电荷水平分布的参数,利用改进的随机放电参数化方案,开展二维高分辨率模拟试验。结果表明:主正电荷区电荷水平分布不均匀且向中心聚集时,产生的闪电类型多为正地闪和正极性云闪,随着电荷水平分布趋于均匀,闪电类型转变为负地闪;主负电荷区电荷水平分布趋于均匀时,闪电类型由负地闪向正极性云闪再向正地闪转变;闪电先导传播特征有较大差异,电荷分布密集不均匀时,先导被束缚在电荷高密度中心,主要在电荷区内发展,当电荷分布单一均匀时,先导能穿出电荷区并水平延伸十几至二十多千米。分析两个电荷区之间的电位分布发现,电荷区电荷水平分布趋于均匀时,位势线向电荷密度中心集中,整个位势阱水平延展,闪电触发点的初始电位值有较大差异,有利于闪电类型和先导传播行为的改变。     

Intracloud discharge and the correlated basic charge structure of a thunderstorm in Zhongchuan, a Chinese Inland Plateau region

The intracloud (IC) discharge is closely related to the charge structure of thunderstorms. The location, charge moment and polarity of intracloud discharges have been analyzed by using the electric field changes from a 7-site network of slow antennas synchronized by GPS with 1 μs time resolution in the area of Zhongchuan in the Chinese Inland Plateau. Ten IC flashes, from a storm on August 20, 2004, have been fitted by using the non-linear least-square solution. The results show that five IC flashes occurred between the main negative charge region and the lower positive charge region and other five between the main negative charge region and the upper positive charge region during the mature stage of the thunderstorm. The centers of discharge were 3.2–5.6 km and 6.8–7.7 km above sea level. The neutralized moments were about 4.56–61.0 C km and 1.06–15.9 C km. It suggests that the charge structure related to the lightning discharge can be represented by a tripole but with a strong positive charge region in the lower part of the thunderstorm, with the lower positive charge region taking an active role in the discharge.     

放电后电荷重置对雷暴云电荷结构及闪电行为的影响

为探究放电后电荷重置对雷暴云电过程的影响,在已有的三维雷暴云起、放电模式中分别加入两种不同的电荷重置方案:一种是植入法即放电后闪电通道上的感应电荷与原空间电荷叠加(简称ZR方案);另一种是中和法即放电后直接按一定比例降低闪电通道处的空间电荷浓度(简称ZH方案)。利用长春一次探空个例进行敏感性试验,发现放电后重置方式的不同会导致闪电特征存在明显差异:1)ZR方案下的云闪发生率比ZH方案下的云闪发生率少。闪电放电后ZR方案在云中植入异极性电荷,对雷暴云中电荷的中和量比ZH方案多,摧毁云中电场的能力更强;2)ZR方案下的正、负地闪发生率均比ZH方案多。相对于ZH方案,ZR方案中主正电荷区的分布范围大于主负电荷区,导致其出现了更多的正地闪;ZR方案中的云顶屏蔽层与主正电荷区的混合程度高,混合时间长,导致ZR方案在主正电荷区与主负电荷区之间触发了更多的负地闪;3)ZR方案下的闪电通道长度比ZH方案下的闪电通道长度短。ZR方案在云中植入异极性电荷,导致云中难以形成大范围同极性电荷堆,闪电通道传播局限在一对较小的异极性电荷堆内,而ZH方案不改变云中电荷分布,存在大范围同极性电荷堆,闪电通道传播范围较大。     

闪电电磁辐射中的爆发式窄脉冲序列分析

分析了发生于闪电放电过程中一类特殊放电现象\_\_爆发式窄脉冲序列。结果表明, 在30 min内测得的69例闪电放电过程中, 全部存在此类爆发式窄脉冲序列。针对6例典型闪电中包含的190例爆发式窄脉冲序列进行了详细分析, 发现窄脉冲典型宽度约为1 μs, 典型脉冲间隔4~8 μs。根据脉冲时间间隔变化和极性转换将其划分为正常型、 反向型、 对称型和反转型。负地闪和云闪产生的爆发式窄脉冲序列特征无明显差别, 而正地闪中的爆发式窄脉冲序列极性反转较为频繁。分析认为, 不同类型的RBPs可能对应流光等击穿过程在不同极性小电荷区间行进的过程。     

Numerical Simulation to Evaluate the Effects of Upward Lightning Discharges on Thunderstorm Electrical Parameters

A theoretical discussion of the discharge effects of upward lightning simulated with a fine-resolution 2D thunderstorm model is performed in this paper,and the results reveal that the estimates of the total induced charge on the upward lightning discharge channels range from 0.67 to 118.8 C,and the average value is 19.0 C,while the ratio of the induced charge on the leader channels to the total opposite-polarity charge in the discharge region ranges from 5.9%to 47.3%,with an average value of 14.7%.Moreover,the average value of the space electrostatic energy consumed by upward lightning is 1.06×10^9 J.The above values are lower than those related to intracloud lightning discharges.The density of the deposited opposite-polarity charge is comparable in magnitude to that of the preexisting charge in the discharge area,and the deposition of these opposite-polarity charges rapidly destroys the original space potential well in the discharge area and greatly reduces the space electric field strength.In addition,these opposite-polarity charges are redistributed with the development of thunderstorms.The space charge redistribution caused by lightning discharges partly accounts for the complexity of the charge structures in a thunderstorm,and the complexity gradually decreases with the charge neutralization process.     

新型人工引雷专用火箭及其首次引雷实验结果

成功研制了一种新型的人工引雷专用火箭, 火箭箭体结构采用了新型复合材料, 质量轻, 并具有空中抛伞和放线功能。利用新型火箭和全新的雷电流及同步电磁场测量技术, 在2009年的山东人工引雷实验 (SHATLE2009) 中成功引发负极性云对地放电过程3次, 共包括6次大电流回击过程, 采用0.5 mΩ的大功率同轴分流器和宽带光纤传输技术测量到了0.1 μs时间分辨率的雷电流波形、以及距雷电通道30 m、60 m和480 m处的电磁场和6000 f/s的高速摄像观测资料。6次回击的电流峰值分布范围为11.2～16.3 kA, 几何平均值12.8 kA; 半峰值宽度为7.4～34.9 μs, 几何平均值21.6 μs; 10%～90%峰值的上升时间为0.5～1.4 μs, 几何平均值1.0 μs。成功的人工引发雷电实验证明新型引雷火箭安全性能好、可靠性高, 其成功研制为雷电物理过程和效应的研究, 以及雷电流波形资料的积累提供了重要的技术手段, 对制定具有我国自主知识产权的雷电防护标准等具有重要的应用价值。     

Inverted-polarity electrical structures in thunderstorms in the Severe Thunderstorm Electrification and Precipitation Study (STEPS)

Balloon-borne electric field soundings and lightning mapping data have been analyzed for three of the storms that occurred in the Severe Thunderstorm Electrification and Precipitation Study field program in 2000 to determine if the storms had inverted-polarity electrical structures. The polarities of all or some of the vertically stacked charge regions in such storms are opposite to the polarities observed at comparable heights in normal storms. Analyses compared the charge structures inferred from electric field soundings in the storms with charges inferred from three-dimensional lightning mapping data. Charge structures were inferred from electric field profiles by combining the one-dimensional approximation of Gauss's law with additional information from three-dimensional patterns in the electric field vectors. The three different ways of inferring the charge structure in the storms were found to complement each other and to be consistent overall. Charge deposition by lightning possibly occurred and increased the charge complexity of one of the storms.Many of the cloud flashes in each case were inverted-polarity flashes. Two storms produced ground flash activity comprised predominantly of positive ground flashes. One storm, which was an isolated thunderstorm, produced inverted-polarity cloud flashes, but no flashes to ground. The positive and negative thunderstorm charge regions were found at altitudes where, respectively, negative and positive charge would be found in normal-polarity storms. Thus, we conclude that these storms had anomalous and inverted-polarity electrical structures. Collectively, these three cases (along with the limited cases in the refereed literature) provide additional evidence that thunderstorms can have inverted-polarity electrical structures.     

Simulation of the Electrification of a Tropical Cyclone Using the WRF-ARW Model：An Idealized Case

Evolution of the electrifi cation of an idealized tropical cyclone （TC） is simulated by using the Advanced Weather Research and Forecasting （WRF-ARW） model. The model was modifi ed by addition of explicit electrifi cation and a new bulk discharge scheme. The characteristics of TC lightning is further examined by analyses of the electrifi cation and the charge structure of the TC. The fi ndings thus obtained are able to unify most of the previous inconsisitent observational and simulation studies. The results indicate that the TC eyewall generally exhibits an inverted dipole charge structure with negative charge above the positive. In the intensifi cation stage, however, the extremely tall towers of the eyewall may exhibit a normal tripole structure with a main negative region between two regions of positive charge. The outer spiral rainband cells display a simple normal dipole structure during all the stages. It is further found that the diff erences in the charge structure are associated with diff erent updrafts and particle distributions. Weak updrafts, together with a coexistence region of diff erent particles at lower levels in the eyewall, result in charging processes that occur mainly in the positive graupel charging zone （PGCZ）. In the intensifi cation stage, the occurrence of charging processes in both positive and negative graupel charging zones is associated with strong updraft in the extremely tall towers. In addition, the coexistence region of graupel and ice crystals is mainly situated at upper levels in the outer rainband, so the charging processes mainly occur in the negative graupel charging zone （NGCZ）.     

北京地区负地闪回击转移的电荷量

负地闪是闪电危害的主要来源,其对地转移电荷源特征和电荷量不仅对闪电放电机理的研究有重要意义,而且对雷电防护也具有重要的实际应用价值。为了研究具有典型城市下垫面环境的北京地区的闪电活动特征和放电强度,利用北京地区2011年两次雷暴过程的多站GPS(Global Position System)同步闪电地面电场变化定量观测资料,在考虑消除场地和环境因素对电场变化观测资料影响的基础上,基于蒙特卡洛数据处理方法和非线性最小二乘法拟合反演算法,定量研究了负地闪回击中和的电荷源位置和电荷量,并对回击特征与回击转移电荷源之间的关系进行了讨论,得到如下结果:(1)单次回击中和的电荷量为1.1~27.6 C,平均为8.6±5.2 C,不同序数回击转移电荷量的最小值基本不随回击序数的上升而变化,最大值和均值随回击序数的上升而减小;一次负地闪中和的总电荷量随着回击数的增加而增加。(2)负地闪回击数和回击时间间隔都呈对数正态分布,其中负地闪总数70.4%的多回击负地闪其回击间隔平均为99±95 ms,不同序数回击的时间间隔最小值随回击序数的上升基本不变,时间间隔最大值和均值随回击序数的上升而减小。(3)回击转移电荷量的均值随回击间隔的增加呈波动形式的逐渐上升;相邻回击转移电荷源的空间距离均值随回击间隔的增加而增大。     

闪电探测技术发展和资料应用

文中综述了闪电探测技术和方法的发展状况, 阐述了闪电监测资料在闪电预警预报、防护以及在灾害性天气监测等方面的应用, 探讨了我国闪电探测站网建设的技术和方法, 以及利用闪电探测资料开展雷电预警预报的方法与途径.闪电探测技术对雷电研究和雷电防护技术的发展非常重要, 特别是随着科学技术的发展, 闪电探测技术得到了快速发展, 这为雷电监测和预警提供了重要手段, 对减少雷电灾害具有重要作用.     

湖北地区一次雷暴云电荷结构和放电特征的数值模拟研究

在三维强风暴动力—电耦合数值模式中引入非感应起电参数化方案、感应起电参数化方案以及放电参数化方案,对湖北宜昌2014年6月19日一次闪电过程中雷暴云电荷结构和放电特征进行了模拟分析。模拟结果表明,当云内粒子增多、增大,大部分霰粒子逐渐降落到中低层,上部正电荷区减小,底部正电荷堆范围开始扩大,中部负电荷区和底部正电荷区成为主要的起电区域,这种底部正电荷区较厚的三极性电荷结构不利于地闪的产生。在粒子带电分析中,霰与冰晶粒子携带的电荷量均大于云滴,说明霰与冰晶之间非感应碰撞是云中主要的起电过程。虽然云滴的电荷量较小,但霰与云滴之间感应碰撞的作用不可忽视。结合电荷结构的分布,发现底部正电荷堆的垂直分布高度与霰粒子、云滴的电荷浓度的分布有关,且霰与云滴电荷浓度的累积区与底部正电荷堆相一致。     

建筑物高度对上行闪电触发以及传播影响的数值模拟

为了探讨建筑物高度对单个上行闪电触发以及传播的影响,设定了一个固定的背景电场,并结合自行触发的上行闪电随机放电参数化方案,进行了二维高分辨率上行闪电放电的模拟试验。结果表明:(1)上行闪电在初始阶段分支比较少;发展到离地面2 km左右后,闪电开始出现大量的分支,闪电通道开始出现明显的分叉:一部分通道继续向高电荷密度中心垂直传播,另一部分通道绕过高电荷密度中心,向外水平传播;模拟的上行闪电只能垂直传播到4 km处的负电荷中心,不能穿过0电势线向上方的正电荷区传播。(2)建筑物高度对上行闪电的触发起了关键作用,建筑物越高,越容易触发上行闪电。(3)建筑物高度对上行闪电传播具有一定的反作用,随着建筑物高度增高,模拟出的上行闪电的水平和垂直传播距离都有所减小,通道的分形维数变小,通道传播的总长度也逐渐减小。     

Latitudinal variations of cloud base height and lightning parameters in the tropics

The observed reduction in cloud-to-ground lightning in the near-equatorial zone is examined from the perspective of the width of the main negative charge region. Thermodynamic observations of cloud base height also show a climatological minimum value in the near-equatorial region. The association of low cloud bases with both narrow updrafts and narrow charging zones may impede the bridging of the large air gap to ground, and thereby suppress cloud-to-ground lightning activity. This width dependence may be more important than the 10% variation in height of the freezing level in encouraging flashes to ground.     

雪崩、分形与雷暴放电中强闪的自组织演化

强调了雪崩、分形与远离平衡系统自组织演化的联系。利用2003年夏季青藏高原中部地区雷暴放电的地面电场野外观测资料,基于近年来发展的分形及多重分形分析中的去势涨落分析(detrend-ed fluctuation analysis,DFA)方法,对强闪前电场信号的关联及多重分形特征进行了分析,发现强放电前过程具有明显的分形和多重分形特征,多重分形谱与推广的二项倍增串级模式符合。分析在一定程度上表明了雷暴强放电发生的可能的自组织演化性。