Lightning activity and its relationship with typhoon intensity and vertical wind shear for Super Typhoon Haiyan (1330)

Super Typhoon Haiyan (1330), which occurred in 2013, is the most powerful typhoon during landfall in the meteorological record. In this study, the temporal and spatial distributions of lightning activity of Haiyan were analyzed by using the lightning data from the World Wide Lightning Location Network, typhoon intensity and position data from the China Meteorological Administration, and horizontal wind data from the ECMWF. Three distinct regions were identified in the spatial distribution of daily average lightning density, with the maxima in the inner core and the minima in the inner rainband. The lightning density in the intensifying stage of Haiyan was greater than that in its weakening stage. During the time when the typhoon intensity measured with maximum sustained wind speed was between 32.7 and 41.4 ms^?1, the storm had the largest lightning density in the inner core, compared with other intensity stages. In contrast to earlier typhoon studies, the eyewall lightning burst out three times. The first two eyewall lightning outbreaks occurred during the period of rapid intensification and before the maximum intensity of the storm, suggesting that the eyewall lightning activity could be used to identify the change in tropical cyclone intensity. The flashes frequently occurred in the inner core, and in the outer rainbands with the black body temperature below 220 K. Combined with the ECMWF wind data, the influences of vertical wind shear (VWS) on the azimuthal distribution of flashes were also analyzed, showing that strong VWS produced downshear left asymmetry of lightning activity in the inner core and downshear right asymmetry in the rainbands.     

Reliability Index of Caisson Breakwaters for Load Variables Correlated

In order to suit the condition that the wave uplift is correlated with the horizontal wave load acting on a vertical breakwater, a generally used method for determining the reliability index β of the breakwater, i.e. the Hasofer-Lind method, is extended in a generalized stochastic space for correlative variables. The computational results for a caisson breakwater indicate that the value of β for the case of correlated variables is obviously smaller than that for the case of independent variables.     

北京闪电综合探测网(BLNET):网络构成与初步定位结果

北京闪电综合探测网(Beijing Lightning NETwork, 简称BLNET)由10个观测站组成, 每个子站主要由闪电快、慢电场变化测量仪(也称快、慢天线)和闪电甚高频(VHF)辐射探测仪构成, 实现了对闪电的多频段的综合观测。本文首先详细介绍了BLNET的网络构成, 然后利用蒙特卡罗法对网络的定位误差进行了理论分析, 模拟结果表明网络内部水平定位误差小于200 m, 网络外部100 km处水平定位误差小于3 km, 最后利用Chan氏算法和Levenberg-Marquardt算法相结合的方法, 对发生在2013年7月7日的一次雷暴过程分别进行了地闪和云闪定位, 将定位结果和对应时次的雷达回波进行比较, 发现地闪和云闪都出现在大于30 dBZ的雷达回波区, 表明了探测网络和定位方法的可靠性。     

中国内陆高原地区典型雷暴过程的地闪特征及电荷结构反演

利用2002年夏季在青海省大通县进行的雷暴及闪电综合观测实验中所获取的6站GPS同步闪电电场变化资料,对8月4日一次下部具有大范围正电荷区的典型性雷暴过程的雷电特征进行详细研究。利用点电荷模式对16次负地闪和2次正地闪所包含的共65次回击所中和电荷源进行的非线性最小二乘法拟合研究发现,负地闪所中和的负电荷距离地面的相对高度在3~5 km,而两次正地闪所中和的雷暴云电荷在5~6 km的高度,表明该雷暴云呈三极性电荷结构。负地闪单次回击所中和电荷量平均为1.48 C,而两次正地闪都为单次回击且中和的电荷量分别为1.37 C和2.68 C。     

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.     

Simultaneous optical and electrical observations on the initial processes of altitude-triggered negative lightning

Using a high-speed camera system and two electric field antenna systems, we have documented the initial processes of an altitude-triggered negative lightning (ATNL). The optical records clearly show that ATNL begins with the inception and propagation of an upward positive leader (UPL) and then a simultaneous propagation of UPL and downward negative leader (DNL), known as the bidirectional leader process, follows. Based on the optical records, it is inferred that (1) the triggering height is about 371 m; (2) the two-dimensional (2D) propagation speed of the UPL in its inception phase is about 3.8–5.5 × 10⁴ m s^− 1 during its propagation from about 393 to 452 m above the ground; (3) the grey levels of the DNL are about one order of magnitude higher than that of the UPL in their inception phase; (4) a discharge phenomenon propagating along the elevated triggering wire part of the lightning channel occurs after the mini-return stroke (MRS), with a 2D propagation speed of about 1.6–2.0 × 10⁵ m s^− 1. Combined with the simultaneous electric field change records, it is further inferred that (1) the UPL incepts about 932 μs earlier than the unstable DNL and about 4.1 ms earlier than the stable DNL; (2) the unstable DNL propagates downward intermittently three times with a time interval of about 1 ms, and each propagation contains a different number of steps with an average step length of about 7 m; (3) the stable DNL incepts at the tip of the unstable one, with a 2D propagation speed of about 1.9 × 10⁵ m s^− 1, an average step length of about 3 m, and a stepping time interval varying from 6 to 31 µs with a mean value of 15 µs.     

Analysis of the Initial Stage Intracloud Lightning Using the Pulse Location Technique Based on the Fast Electric Field Change

Academy of Sciences,Beijing 100029 2 Lanzhou University,Lanzhou 730000 3 Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences,Lanzhou 730000 4 Nanjing University of Information Science＆Technology,Nanjing 210044
Using both fast and slow electric field change sensors and field mill,multi-station observations on lightning flashes over China inland plateau areas were conducted during the summer of 2004.All of the stations were synchronized by GPS with a time-resolution of±50 ns.Using the different time of arrival（DTOA）and based on the fast electric field change sensor,a lightning radiation location technique was developed.Radiation pulses in the initial stages of five intracloud（IC）lightning discharges which occurred on 20 August were analyzed.The results indicate that the technique developed could effectively locate the lightning radiation sources.Furthermore,the lightning discharges were compared with the Doppler radar data.The results show that the radiation sources were well associated with the storm development.When the storm was at the mature stage with an echo top of about 10.9 km,the radiation sources ranged from 5.2 to 8.3 km above mean sea level;when the storm gradually became weaker,with echo top of about 7.9 km,the radiation sources ranged from 3.0 to 5.9 km.In particular,one of the IC lightning discharges ranged from 3.0 to 4.9 km during the dissipation stage of the storm.The results also indicate that the radiation sources were closely associated with the high reflectivity region（25–50 dBZ）of the storm,which,to some extent,demonstrates the reliability of the location results,thereby showing that multi-station observations of fast electric field change sensors could be a useful tool for monitoring the storm development.Location errors from radiation sources were also compared with the radar data and the results of a simple simulation.It was found that the errors were getting smaller when the radiation sources approached the center of the detection network, and vice versa.Compared with the limited experimental observations,the simulation results were found capable of effectively reflecting the location errors.     

短基线时间差闪电辐射源探测系统和初步定位结果

介绍了一种新型的闪电探测设备———短基线时间差法辐射源定位系统,并选取2002年夏季野外观测实验中的辐射源定位结果,结合电场变化特征分别对两次地闪和云闪进行了分析。结果表明,该系统对地闪先导过程和云闪产生的辐射源能够较好地定位。定位结果的个例分析证实,观测地区的两次云闪放电过程都由起始于云下部负电荷区的负极性击穿引发,然后向上发展到上部正电荷区,通道的发展速度约为1.29×105m·s-1,地闪梯级先导的传播速度约为1.73×105m·s-1。     

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。     

雷暴云不同空间电荷结构数值模拟研究

利用一个三维时变双参数动力电耦合模式对决定雷暴云空间电荷结构的三个初始场：反转温度、中心最大扰动位温和扰动区域进行模拟对比研究。结果表明,选取不同的参数值,雷暴云电结构有很大差异,从而解释了在不同地区、季节、强度的雷暴云中所观测到得不同的空间电荷结构的原因。