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.     

吉林地区一次雷暴云个例电和云微物理特征的模拟分析

利用三维强风暴动力一电藕合数值模式, 结合闪电定位仪资料、雷达回波资料及降水资料,分析了吉林地区一次雷暴云个例在发生第一次闪电前云内电场的发展情况及微物理变化过程,并与青藏高原一次典型雷暴过程进行了对比.结果表明:云发展成熟时,云中呈现上正下负及云下部次正的三极性分布,主负电荷区稳定在-10℃层附近,次正电荷区浓度较大;上升气流穿过-15℃层之上开始强起电;云中最大电场出现在上升速度达到最大值后回落的阶段;闪电频数与云发展的高度及回波强度有关,回波强度＞45 dBz时,云发展越高,闪电频数越大,云顶高度＜6 km时,闪电发生较少;青藏高原雷暴具有与我国北方雷暴明显不同的特征.     

Description and first results of an explicit electrical scheme in a 3D cloud resolving model

The three-dimensional non-hydrostatic mesoscale model MésoNH of the French community offers the numerical environment to develop a cloud electrification scheme in a consistent way with the original mixed phase microphysical scheme. The charge separation mechanisms are entirely due to non-inductive processes and result from elastic ice–snow, ice–graupel and snow–graupel collisions. The electric charges carried by each of the five hydrometeor categories are transported along the airflow and are exchanged according to the various microphysical mass transfer rates but assuming a power law distribution of the individual charges as a function of the particle size. The electric field is diagnosed at each time step after integrating the electric potential induced by a net charge density in the Poisson equation. Finally, a lightning ash is triggered when the electric field locally steps over a given threshold. It propagates in two opposite directions until the magnitude of the electric field falls below a prescribed value. A fractal branching algorithm is then activated to extend lightning streamers away from the main channel and toward cloudy regions where substantial charge densities are present. Charges are neutralized along the tortuous lightning path with a simple procedure that preserves total charge conservation.The complete electrification scheme tested for an ideal case of vigorous supercellular storm shows an intense electrical activity all along its lifecycle. We show that the model is able to produce a direct tripolar structure of the charges as the result of a temperature charge reversal of − 10 °C and of the different sedimentation rates of the hydrometeors.     

安徽闪电分布特征和不稳定条件分析

利用安徽2008—2011年LD-Ⅱ型闪电定位系统资料,以统计方法分析安徽闪电分布特征,发现安徽闪电的发生较为集中在7—8月,闪电极性以负闪为主(约占总闪的93%以上),同时存在南北差异。南部的闪电数和平均电流强度比北部大,但北部正闪比例略高于南部。进一步结合2008—2011年阜阳、安庆两站探空资料,选取了抬升指数、对流有效位能、700~400 hPa平均相对湿度、700 hPa假相当位温、850~500 hPa温差、沙氏指数与K指数7个大气不稳定参数,以两站为中心的0.5个纬距范围内,分析了探空放球时间后6 h内,大气不稳定参数与闪电活动的关系,确定了闪电活动的不稳定参数阀值,为闪电活动预报奠定基础。     

一次雹暴的闪电特征和电荷结构演变研究

综合利用SAFIR3000三维闪电定位系统的全闪定位资料与雷达结合对2005年5月31日发生于北京的一次冰雹过程的闪电活动和电荷结构演变特征进行了综合分析.结果表明:该雷暴的闪电活动有两次活跃期,第一个活跃期产生了降雹,降雹结束后,闪电活动突然减少,之后的活跃期产生了更多的闪电,其中一部分处于云砧区.闪电活动峰值超前降雹5 min左右,闪电活动中的地闪仅占6.16%,但正地闪占总地闪的比例达20%,且降雹前的正地闪比例较降雹后要高·降雹发生后,正地闪很少发生.降雹阶段,参与放电的主要电荷区表现为反极性结构,-40℃左右区域为参与放电的主负电荷区,-15℃左右区域为参与放电的主正电荷区,在正电荷区之下,短暂存在一个较弱的负电荷区.降雹结束后,电荷结构经历了持续的快速调整过程,在第2次闪电活跃期,参与放电的主要区域表现为正常的三极性结构,即上正-中负-下正,受西风气流的影响,此三极性结构出现倾斜.动力和微物理过程的分析表明,闪电活动和电荷结构的特征与雷暴云内的动力、微物理过程紧密相关.文中对反极性电荷结构形成的可能机理进行了讨论,并且认为,具有强烈上升气流的灾害性天气可能更易形成反三极性的电荷结构,并在下部两个电衙区的作用下产生较多的正地闪.     

青藏高原雷暴云降水与地面电场的观测和数值模拟

在2003年青藏高原那曲地区夏季雷暴云的观测试验中,三次伴有降水的过程中都出现了地面电场(Egnd)随降水的漂移现象,而且固态和液态降水对Egnd的极性改变并不相同。为了模拟再现高原雷暴云降水和Egnd之间的关系,选取了8月13日这次具有高原雷暴代表性特征的过程,模拟了雷暴云移经观测点上空期间,测站固、液态降水与Egnd的变化以及雷暴云下部正电荷区的空间分布。模拟的Egnd及固、液态降水与其的对应关系与观测事实较一致。分析结果表明,固态降水主要携带正电荷,液态降水主要携带负电荷,各类带不同极性和数量电荷的降水粒子常共存在雷暴云中,Egnd主要受携带电荷量占主导地位的降水粒子的影响,地面出现强正电场时正好是云在当顶并且地面出现强固态降水的时间。     

The electrification of dust-lofting gust fronts (‘haboobs’) in the Sahel

Two Doppler radars and a suite of auxiliary surface observations are used to document the electrical, aerosol and aerodynamic properties of dust-lofting gust fronts near Niamey, Niger during the AMMA (African Monsoon Multidisciplinary Analysis). Electrification with dominant negative polarity is a common behavior, consistent with earlier studies on dust devils and the Harmattan wind in dry environments.     

Lifetime of the thunderstorm electric energy in the global atmospheric circuit and thunderstorm energy characteristics

The lifetime of electric energy in the atmosphere is introduced and investigated as is the total electric energy of the atmosphere related to the total mean rate of electric energy dissipation. This lifetime, as determined from general estimations and convenient analytical expressions, turns out to be very small – from about 10 to about 100 s, depending on the assumptions on the control parameters of principal sources in the global electric circuit. In particular the energy lifetime is less than the relaxation time of the “global condenser” and field relaxation time near the ground surface. It is explained by the high dissipative rate of the electric energy in the atmosphere, taking into account that the regions mainly contributing to the total energy and its dissipative rate are connected to the altitudes of active parts of electrified (thunderstorm) clouds in the atmosphere with exponentially increasing conductivity.     

On the generation of charge layers in MCS stratiform regions

We suggest a quantitative one-dimensional model treating the formation of charge layers near the 0 °C isotherm in stratiform regions of mesoscale convective systems. A number of factors principal for the field generation have been taken into account: both non-inductive and inductive melting charging, light ions, a complicated profile of the vertical air velocity near the 0 °С isotherm, the boundary conditions proper for the horizontally extended systems in the global electric circuit. Non-inductive collisional charging near the 0 °C isotherm was not considered. It was found that both non-inductive and inductive melting mechanisms can contribute; the inductive melting charging of ice aggregates was found more preferable, while the contribution of non-inductive mechanisms might be significant depending on particular conditions. The role of light ions in the formation of the positive charge layer near the 0 °C isotherm may be important. If the advection from the convective region ensures charge inflow to the upper charged layers, the melting charging mechanisms are able to explain an observable electric field structure in the whole stratiform region. It is important that the mutual position of the zero point on the vertical air velocity profile and the point of maximum melting-charge-transfer determines the fine structure of the electric field in the vicinity of the 0 °C isotherm.     

Multiple pulses in dE/dt and the fine-structure of E during the onset of first return strokes in cloud-to-ocean lightning

We have analyzed the fine-structure of 131 electric field (E) waveforms that were radiated during the onset of first return strokes in cloud-to-ocean lightning. The dE/dt waveforms were recorded using an 8-bit waveform digitizer sampling at 100 MHz, and the E waveforms were sampled at 10 MHz using a 10-bit digitizer. 49 (or 37%) of the dE/dt waveforms contain one or more large pulses within ± 1 μs of the largest (or dominant) peak in dE/dt, i.e. within an interval from − 1 μs to + 1 μs, where t = 0 μs is the time of the dominant peak, and 37 (or 28%) have one or more large pulses in the interval from 4 μs before to 1 μs before the dominant peak, i.e. − 4 μs to − 1 μs, and only the dominant peak within ± 1 μs . We give statistics on the amplitude and timing of dE/dt pulses that are near the dominant peak, and we show how the presence of these pulses adds considerable fine-structure to the shape of E_int, the integrated dE/dt waveform, on a time-scale of tens to hundreds of nanoseconds. This fine-structure includes fast pulses near the beginning of the slow front, large pulses and shoulders within the slow front and during the fast-transition, and very narrow peaks in E_int. Our overall conclusion is that the electromagnetic environment near the point(s) where lightning leaders attach to the surface is often more complicated than what would be produced by a single current pulse propagating up a single channel at the time of onset.     

甘肃中部强对流天气多普勒雷达和闪电特征个例研究

利用雷达和闪电资料对2004年5月15日甘肃中部的一次强对流天气过程进行了综合分析。通过分析,得到了冰雹降水的一些中小尺度多普勒雷达特征和闪电与雷雨、冰雹发生、发展的关系。在强对流系统发生、发展的过程中,当回波强度>40dBz时就伴随有闪电发生。冰雹云中存在空间上很靠近的强度梯度和速度梯度大值区;含水量最大值区与强度最大值区相对应;在径向速度图上表现出低层辐合、高层辐散的特征。     

空中人工引发雷电的正负先导特征研究

通过对 1998年 8月 2 2日空中引发雷电先导过程的光、电观测资料的综合分析发现 ,在空中引发雷电的先导系统中存在三个先导过程。①向下发展的负先导在起始阶段呈小阶梯特征 ,阶梯之间的时间间隔约为 2 0 μs ,阶梯的上升时间小于 1μs,随着负先导的下行发展 ,梯级增长。②金属导线上端向上发展的正先导在负先导接地之后 ,表现出明显的阶梯特性 ,阶梯之间的时间间隔平均为 15 μs。③从地面向上发展的连接正先导由多个振荡脉冲组成 ,脉冲之间的时间间隔约为 13μs,连接先导的发展也是梯级的。电场快变化中的高频分量随着距离的增加衰减很快。最强的发光是由向下的负先导接地时形成的小回击产生的 ,强光只集中在空气离化而形成的放电通道部分 ,光强则随着高度的增加很快衰减 ,其传播速度约为 2 .1× 10 8m·s-1。在小回击发生之前 ,向下发展的负先导在接地之前有较强的发光 ,而金属导线上端向上发展的正先导没有明显的发光。在小回击发生之后 ,金属导线上端向上正先导的发光强度被增强 ,其向上的传播速度约为 2 .4× 10 6m·s-1。金属导线部分在小回击发生之后约 2 2 0μs逐渐开始熔化发出强光 ,并向上发展而与前面向上发展的正先导的发光相并合 ,其传播速度约为 1× 10 6m·s-1     

ECMWF极端天气指数在新疆强降水预报中的检验评估

使用2015年10月—2018年9月欧洲中期天气预报中心集合预报系统(ECMWF EPS)逐日降水极端天气指数(EFI)预报资料,分析新疆区域降水EFI产品与强降水的对应关系并得到预报阈值。结果表明:预报的EFI与实况降水量存在正相关关系,随着降水量增加,EFI预报结果具有线性增加趋势,说明EFI对强降水有一定的指示意义。各量级降水预报的最高TS评分随着预报时效的增加而减小,且随着降水量等级的增大而减小。不同季节暴量降水发生站次为夏季最多,冬季最少,对应的EFI阈值大都在0.4～0.6,夏季EFI值范围在0.2～0.7,夏季更易发生暴量降水。随着预报时效增加,暴量降水发生站点频次最多所对应的EFI值逐渐减小。随着降水量级增加,空报率减小幅度不大,但漏报率增加。     

Cosmic rays and the electric field of thunderclouds: Evidence for acceleration of particles (runaway electrons)

We present the data on correlations of the intensity of the soft component of cosmic rays with the local electric field of the near-earth atmosphere during thunderstorm periods at the Baksan Valley (North Caucasus, 1700 m a.s.l.). The large-area array for studying the extensive air showers of cosmic rays is used as a particle detector. An electric field meter of the ‘electric mill’ type (rain-protected) is mounted on the roof of the building in the center of this array. The data were obtained in the summer seasons of 2000–2002. We observe strong enhancements of the soft component intensity before some lightning strokes. At the same time, the analysis of the regression curve ‘intensity versus field’ discovers a bump at the field sign that is opposite to the field sign corresponding to acceleration of electrons. It is interpreted as a signature of runaway electrons from the region of the strong field (with opposite sign) overhead.     

2013年5月华南强降水与中国南海夏季风爆发

利用2013年"华南季风强降水外场试验与研究"的外场试验数据、美国NCEP FNL资料和卫星云顶黑体辐射温度资料,对2013年5月7—17日华南地区出现的两次强降水过程(7—12日和14—17日)中的高低空环流以及相关气象要素场的变化进行了对比分析。中国南海夏季风于5月第3候建立,两次过程分处于夏季风爆发前后。通过对比影响两次强降水过程的主要环流系统如南亚高压、高空副热带西风急流、500 hPa环流型、水汽来源等,指出影响两次强降水过程大尺度环流场之间的显著区别,说明南海季风爆发前后大尺度环流场对暴雨影响的典型差异。7—12日过程主要受北方锋面影响和南方暖湿气流辐合作用,导致华南地区出现南北两条雨带。14—17日过程则由于季风爆发后强的暖湿空气活动致使华南地区对流活跃,从而形成一条位于广东北部的雨带,此次过程强降水比第1次过程集中且对流性更强。两次降水过程的内在物理机制是一个准平衡态的热力适应过程,由于第2次过程降水更强,导致热源作用明显增强,动力向热力的适应过程也更显著。利用探空资料揭示出两次过程暖区暴雨大气热力和动力条件存在显著区别,7—12日南海季风爆发前的暖区暴雨主要受低层强垂直风切变导致的大气斜压不稳定影响;14—17日南海季风爆发后的暖区暴雨主要受高低空急流的强耦合作用影响。     

乌鲁木齐市强降水雷达回波特征分析及预报研究

利用乌鲁木齐市2004年和2005年的夏半年(5月至9月)新一代雷达降水模式的产品资料及相应的天气图、实时降水量等资料,对乌鲁木齐市强降水个例的降水时雷达回波强度和范围、不同类型性质降水的移速及移向进行了分析研究。得出:当强降水过程(1h内)组合反射率因子强度都在35dBz以上,并出现强度40dBz以上、范围在20km×25km以上且能移过当地时就会出现1h降水量>6mm以上的强降水,概率达75%。当出现强度40dBz以上、范围在20km×25km以上并有成块的>50dBz以上强度的回波且能移过本地时,则会出现雨强很大的短时强阵性降水;连续性强降水的雷达回波移速平均为0.5km/min,阵性强降水雷达回波移速为1km/min;利用雷达产品中速度方位显示风廓线(VWP)的4～5km高度的风向做雷达回波移动方向的临近预报。所得结果应用价值大,对乌鲁木齐市短时临近强降水预报具有一定的指导性,在短时临近强降水预报的服务工作中将会产生很大的社会效益和经济效益。     

首次回击具有双接地点的地闪光学和电学特征的个例分析

利用成像率为1000幅／s的数字化高速摄像系统和时间分辨率为1μs的快、慢天线闪电电场变化测量仪在广州附近观测到一次首次回击具有两个接地点的负极性地闪。两个分支到达地面的时间间隔约为30μs;在发生回击R2时,其中一个分支的直窜先导发展成为企图先导。观测发现M一分量的发光要比梯级先导强;回击间的K一变化与云中的在击穿和通道的延伸有关,但不引起云地间通道的发光。光学和电场变化的同步观测证实了直窜一梯级先导的发展速度与前一次回击的时间间隔有关,较快的先导发展速度对应于较短的回击时间间隔,较慢的发展速度对应于较长的回击时间间隔。另外,本文在资料分析的基础上,提出了产生双接地点的四种可能原因。     

Apposite of atmospheric electric parameters with the energy coupling function (ε) during geomagnetic storms at high latitude

In this paper we are concerned with the variation of the atmospheric electric field and the air–earth current due to the excessive power generated by the solar wind-magnetosphere dynamo during geomagnetic storms, recorded at Maitri in Antarctica during 2004. A major part of the power generated by the solar wind-magnetosphere dynamo is used in the formation of the ring current and the rest is utilized for Joule heating and auroral particle precipitation. The method adopted by Frank-Kamenetsky et al. [Frank-Kamenetsky A.V., Troshichev O.A., Burns G.B., Papitashvili V.O., 2001. Variations of atmospheric electric field in the near-pole region related to the interplanetary magnetic field. J. Geophys. Res. 106, A1, 179–190.] was utilized to delineate the variations due to the signatures of tropical thunderstorm activity from the geoelectric data; while statistical methods used in our earlier studies were used to delimit variation due to the constant buffeting of the solar wind. We find that the solar wind-magnetosphere energy coupling function (ε) to be well correlated with the atmospheric electric parameters during the onset of geomagnetic disturbances. However the correlation breaks down during minor storms and sub-storm events.     

闽北强对流天气的短时监测及判别方法研究

利用2005-2009年的闽北冰雹、大风、短时强降水过程所对应的闪电资料产品,分析了闪电资料在各类不同性质的天气过程中的表现特点;用2008年10月至2010年4月的大气电场资料对不同类型天气的表现特点进行了分析,得出一些有益的结论。这些分析可加强业务人员对闪电资料产品和大气电场资料的认识,对今后闪电资料和大气电场资料在预报业务中的应用具有一定参考意义。研究发现利用闪电定位资料和大气电场资料对闽北强对流天气进行短时监测和判别预报具有定性明确、客观化程度较高等优点,在业务实践中有较高的应用价值。     

湖北省雷暴日数与云地闪电密度关系研究

为了研究年雷暴日数与雷击大地年平均密度关系,以满足雷电防护工程设计、雷击风险评估和雷电灾害防御工作需要,采用湖北省ADTD雷电监测定位系统探测的2007--2010年云地闪电资料和雷电监测理论探测效率在95％以上的28个气象台站的年雷暴日数,对台站周围不同半径距离范围内年平均云地闪电次数与年平均雷暴日数进行统计分析。结果表明：在台站周围18～20km范围内,相关系数明显增大,其中18km范围内相关系数最大为0．8521。由此可以认为,观测人员一般只能听到观测站点周围18～20km左右的雷声。经统计计算,拟合年平均雷暴日数与雷击大地年平均密度关系式为：Nc=0．029Td^1.5。通过2011年检验表明,采用拟合方程：Nc=0．029Td^1.5计算各台站雷击大地年平均密度明显优于规范方程：Nc=0．024Td^1.3计算的效果。