Attempts to create ball lightning with triggered lightning

We describe attempts to create ball lightning by directing lightning, triggered from natural thunderclouds using the rocket-and-wire technique, through a variety of materials. Some of the observed phenomena have features in common with natural ball lightning or with laboratory attempts to create it: flame-like luminosity for up to 0.5 s above salt water; constant-luminosity silicon fragments falling for about 1 s under the influence of gravity; a 0.7 m region of stationary luminosity whose bottom was 0.3 m above a stainless steel surface to which arcing had occurred; and a glow for about 0.5 s above pine tree sections.     

On lightning forecasting

Summary An exact forecasting of lightning is not possible so far. On the other hand situations occur to-day more often than in earlier times in which the best lightning protection is not sufficient to prevent harmful effects of lightning strokes. For this reason it should be attempted to use informations from the field of atmospheric electricity to improve the existing possibilities of lightning forecasting. These improvements are shortly pointed out, further experiments are under way.

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Zusammenfassung Eine genaue Blitzvorhersage ist bis jetzt nicht möglich. Da aber Situationen, in denen auch eine gute Blitzschutzanlage schädliche Blitzwirkungen nicht mehr ausreichend verhindern kann, heute häufiger als früher vorkommen, muss wenigstens versucht werden, die luftelektrischen Erkenntnisse für eine Verbesserung der Vorhersage von Blitzschlägen zu verwenden. Hier gegebene Möglichkeiten werden erwähnt, weitere Versuche sind im Gange.

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Résumé Nous sommes encore très éloignés de la possibilité de prédire exactement la foudre. Mais, dans la pratique, la nécessité d'améliorer les méthodes de prédiction, en usage jusqu'à maintenant, ne peut pas être désavouée, parce qu'il y a de plus en plus installations, opérations et instruments sensibles pour lesquelles aussi la meilleure protection contre la foudre ne serait plus suffisante. Des possibilités données pour ce but sont discutées, tandis que des nouveaux expériments on été mis en train par l'auteur.

     

Spatiotemporal characteristics of positive cloud-to-ground lightning discharges and bidirectional leader of the lightning

The negative CG lightning discharges neutralizing negative charges in cloud usually dominate for most of thunderstorms. However, a lot of positive CG light-ning discharges often occur in the disappearing stage of thunderstorms, in the stratiform region of mesoscale convective systems and some supercells producing hail and tornado. Because the positive CG lightning discharges produce larger current of the return stroke and neutralize more charges due to the continuing currents with longer las…     

Estimation of lightning and sprite parameters based on observation of sprite-producing lightning power spectra

Spectrograms and ELF power spectra of magnetic variations originated from sprite-producing lightning discharges have been analyzed to extract both parent lightning and sprite parameters. Some of the spectrograms and power spectra have been found to have approximately quasi-oscillatory shape in the frequency range 0–40 Hz with maximum repetition period about 15–20 Hz. A theory predicts that this interesting peculiarity of the power spectra can be due to interference between electromagnetic fields originated from the parent lightning discharge and from the sprite. A smooth envelope of the power spectrum was shown to have a form of damped oscillations with period close to reciprocal value of sprite lag time. A technique of extracting sprite parameters based on the sprite-producing lightning power spectrum is proposed. The lack of the first Schumann resonance and other features occasionally observed in spectral resonance structure were also discussed.     

Estimate of NOX production in the lightning channel based on three-dimensional lightning locating system

Based on the VHF lightning locating system,a three-dimensional-space cell-gridded approach is used to extract the lighting channel and calculate the length of the channel.Through clustering of the located radiation sources and then extracting the lightning channel,it can accurately obtain the length of the channel.To validate the feasibility of the approach,a simulation experiment is designed,and it shows the length error is no more than 10%.The relationship between the NO production of per unit arc length and atmospheric pressure obtained in laboratory is applied to the NOX production of per unit flash length at different altitudes in this paper.The channel length and the NOX production of 11 negative cloud-to-ground flashes and 59 intracloud flashes in an isolated thunderstorm in the northeastern Qinghai-Tibet Plateau are calculated.The results show that the average channel lengths of per cloud-to-ground and intracloud flash are 28.9 and 22.3 km respectively;the average NOX productions of per cloud-to-ground and intracloud flash are 1.89×1025 and 0.42×1025 molecules,respectively.     

Wavelet analysis of lightning return stroke

In this investigation, time series consisting of electric field waveforms of 15 positive return strokes and 10 negative return strokes were analyzed. The data came from a summer thunderstorm in March in a range of about 200 km around São José dos Campos, São Paulo. The electric field recording system consisted of a flat plate antenna with a decay time constant of 260 μs and a sample rate of 800,000 samples per second. The bandwidth observed was up to 100 kHz and the recording system was synchronized with GPS time and located at São José dos Campos. Wavelet analysis of the electric field waveforms was done in order to investigate the behavior of the return stroke spectrum in time. The return stroke was suggested to be divided into two portions: initial stage and overshoot (for far return stroke) and initial stage and ramp (for close return stroke). The return stroke power spectrum was observed to be distributed in a frequency range with the peak value also distributed in a fraction of this range. Power peaks for ramps are stronger than power peaks for initial stage and overshoot. Finally, it was observed how powerful the wavelet is in the analysis of lightning.     

Using lightning locating system based on time-of-arrival technique to study three-dimensional lightning discharge processes

A time-of-arrival(TOA) system based on GPS technology for locating VHF radiation sources from lightning has been developed and used in observation sites in the northern Shandong Province,China.The 3D images of the lightning progression have been obtained successfully for the first time in China.The 3D-channel evolutions of typical negative CG,positive CG and IC lightning flashes have been discussed together with the data of fast electric field change.It was found that significant differences existed between the negative and positive CG lightning flashes in terms of the initiation and propagation of the radiation sources.The preliminary breakdown of a negative CG lightning flash propagated at a speed about 5.2×104 m/s.The stepped leader of negative CG lightning flashes was trigged by negative initial breakdown.Thereafter,it propagated downward at a speed of 1.3×105 m/s.The initial process of the positive CG lightning flashes was also a propagation process of negative streamer.These streamers propagated dominantly horizontally in the positive charge region and accumulated positive charges at the origin of the lightning,and as a consequence,initiated downward positive streamers.A new type of lightning discharge that was triggered by a narrow bipolar pulse(NBP) is discussed in this study.The NBP was originated at altitude of about 10.5 km in the upper positive charge region.As a distinct difference from normal IC flash,its channels extended horizontally all around and produced a lot of radiation sources.The source power of the NBP could approach 16.7 kW,which is much greater than that of normal lightning discharge ranging between 100 mW and 500 W.The 3D propagation of this new type of lightning discharge was observed and obtained for the first time in China.The possible initiation mechanism of this new type of light-ning is discussed here.     

Characteristics of Japanese winter sprites and their parent lightning as estimated by VHF lightning and ELF transients

Sprites are newly discovered optical emissions in the mesosphere over large thunderstorms. This paper is the observational summary of winter sprites in the Hokuriku area of Japan and their parent lightning in the winter of 2004/2005, by using the coordinated optical and electromagnetic (VHF and ELF) measurements in Japan. As the results of optical observations at two stations, we have found that this campaign has yielded a variety of sprite shapes; V-angle shaped structures have been often observed (25%) in addition to columnar structures familiar for us. All of the sprite events are found to be associated with $+$CG lightning, as seen from the macroscopic information by ELF data at Moshiri. However, examining the microscopic properties of parent lightning as seen from the VHF SAFIR lightning detection network, has suggested very complicated characteristics of parent lightning discharges inducing sprites, as compared with the ELF data. One half of the sprite events are also found to be associated with $+$CG by the SAFIR observation, but another half has yielded rather new results as compared with earlier results. Four events are definitely associated with $-$CG and the remaining three events, inter-cloud flashes. The overall picture for Japanese winter sprites and their parent lightning discharges, is significantly different from that for the summer-time, continental sprites. This is indicative of complexity of winter lightning in the Hokuriku area of Japan and this would provide new information on the sprite generation mechanism.     

Time resolved simulation of lightning by lip

In this letter, we report results of time resolved spectra of lightning simulation in air by laser-induced plasma (LIP). The measured electron temperatures varied from (1.7 +/- 0.1)X10(4) K at 600 ns to (1.2 +/- 0.1)X10(4)K at 4 microseconds after the ignition of the plasma. Electron densities in the plasma varied from (7.0 +/- 1.4)X10(17)/cm3 to (9.0 +/- 1.8)X10(16)/cm3 for the above times. We also present, for the first time, a comparison of state variables for LIP and natural lightning. We find that immediately following the ignition both natural lightning and LIP reach temperatures in excess of 16,000K and relax to ambient pressure with different rates. They are expected to approach 2000 - 4000 K temperature range, which is important to chemical synthesis, in an asymptotically similar fashion.     

Ball lightning as a radiation bubble

Summary A model for ball lightning is presented and its properties discussed. The model is that of a microwave radiation field contained within a plasma dielectric sphere, resonant at a frequency much greater than the electron-molecule collision frequency. Calculations are made of the energy stored in the microwave field, the electron temperature, the rate of energy loss due to ionization, and the effects of recombination. It is concluded (a) that a self-consistent set of conditions can be obtained only when the neutral density within the sphere is much lower than atmospheric, and (b) that the microwave field strength required is of the order of 10⁹V/m. Under these conditions the radiation pressure becomes comparable to that of the atmosphere; the second case investigated is when these two become equal. It is then found that this radiation bubble appears to satisfy the requirements imposed on energy storage and dissipation, recombination and resonant frequency. The electron density in such a bubble is found to be typically 10¹¹ cm^–3 and the stored energy typically 10³ Joules. A discussion is given of some of the problems associated with the model-formation, stability, neutral number density, and the problem of hydrostatic equilibrium.     

Genesis of the Nyiragongo lavas

Mt. Nyiragongo is one of the eight major volcanoes of the large Virunga volcanic field in the Lake Kivu area in the Eastern Congo. The lavas of Nyiragongo are rather unique. Starting from the top of the mountain, the rocks are nephelinites with some leucite and melilite. The molten material of the present-day lava lake belongs to this type of lava. Under the nephelinites, there is a thin series of leucite-rich lava beds. The main part of the volcano consists of bergalitic melitite lavas alternating with pyroclastics of similar composition. The nephelinitic material is considered to constitute the main portion of the pre-volcanic magma under the future volcano. It is pointed out that the Nyiragongo represents just the type of volcano with which the African volcanic carbonatites are associated. It is concluded that the Nyiragongo nephelinite must be interpreted in a way accepted for the Central African volcanic nephelinites in general. The bergalitic melilitite material is interpreted as a product of carbonation of the nephelinitic magma.     

Properties of preliminary breakdown processes in Scandinavian lightning

Lightning flashes are usually preceded by preliminary breakdown processes (PBPs) before a stepped leader is initiated. These breakdown processes are not well understood. An early model, the so-called BIL model, has been called into question in later studies. However, we have found that the BIL model is quite successful in describing initial processes at least in high-latitude Scandinavian lightning. We present results from one summer of measurements in Finland, during which the vertical electric field was measured with a standard broadband plate antenna system. Lightning flash locations were provided by a lightning detection network and magnetic fields were measured with an experimental narrowband detection system. The relationship between the preliminary breakdown and the first return stroke (RS) is studied for 193 flashes at distances of 5–70 km. We can identify a preliminary breakdown in at least 90% of the flashes. The peak electric field of the RS is on average four times as intensive as the highest peak of the PBP. However, in 25% of the cases the PBP peak is more intensive. On the other hand, we show that this method of comparing intensities is physically arbitrary, since the PBP is continuous and the RS is impulsive. The narrowband measurement allows a physically consistent definition for intensities as the root-mean-square (RMS) sum of the most intense parts of signals. The PBP and RS are shown to have almost equal intensities at small distances. At larger distances, the PBP weakens more rapidly. This is suggested to be due to different propagation regimes, with the PBP signal changing from space-wave to ground-wave propagation with increasing distance, while the RS is predominantly ground wave at all distances. The result may have practical applications in narrowband detection of lightning. The BIL model suggests a characteristic signal in the narrowband signal, which could be used to identify the start of a lightning flash. The change in the RS–PBP ratio as a function of distance is statistically significant, but is too weak to significantly improve ranging methods.     

地闪先导放电三维数值模拟

为探索地闪先导放电规律以满足新型雷电防护理论与技术研究的需要,在Amoruso和Lattarulo提出的带电圆盘雷云荷电解析模型框架下,利用三维WZ模型构造了地闪先导放电数值模拟算法,第一次实现了50 m空间分辨率的地闪先导放电三维数值模拟.在解析模型框架下,求解空间大幅缩小,使高分辨率模拟成为可能.模拟过程中采用了SOR法求解七点差分格式的拉普拉斯方程,提出了双概率指数建模思想,对WZ模型进行了修正,反映了真实先导主通道的延伸性与丰富分岔的分形特征.进行了不同发展阈值下的模拟实验,得到了精细的地闪双向先导三维放电图样与先导激励下的地面电场分布,结果在一般观测范围内.     

Neutron generation mechanism correlated with lightning discharges

The results of the experiments, during which we revealed that the flux of neutrons in the atmosphere increases in correlation with electromagnetic pulses of lightning discharges, have been analyzed. The mechanisms of charged particle acceleration and nuclear reactions that can be responsible for neutron generation have been analyzed. It has been indicated that the probability of nuclear synthesis reactions in a lightning channel, which is traditionally considered as the source of neutrons in a thunderstorm atmosphere, is extremely low. The generation of neutrons in thunderstorm electric fields is related to photonuclear reactions in gigantic upward atmospheric discharges caused by relativistic runaway electron bremsstrahlung.     

闪电电场变化测量仪研究

分析了现有闪电电场变化测量仪存在的不足之处,提出了采用一台测量仪同时获得闪电电场快、慢变化特性的技术方案,通过对测量仪天线、电路、传输方式的优化,大大降低了系统的复杂程度,提高了可靠性;采用全介质光缆传输信号,可避免在信号传输过程中因电磁耦合带来的干扰;采用系统函数逆变换反演被测电场时域特性,既可省去一套专测电场慢变化的仪器,且弥补了以往"电场慢变化测量仪"性能的不足.测量结果表明,快变化测量系统的测量带宽为80 Hz~87.5 MHz.采用研制成的电场变化测量仪对自然闪电进行多次测量后,将反演运算得到的波形与实测波形对比,验证了所提方案的可行性和技术上的先进性.     

Genesis and differentiation of nephelinitic magma

Bulletin of Volcanology - The possibility of formation of nephelinite magma from picrite magma by separation of eclogitic fraction is discussed from experimental results on some picritic rocks....     

Genesis and evolution of gypsum tumuli

Tumuli are hollow subcircular domes of the most superficial stratum of gypsum, principally found in outcrops of macrocrystalline gypsum. They vary from a few centimetres to several metres in diameter and reach maximum heights of a little more than 1 m. The relationships between the morphostatistical parameters that define these formations are: h = r/3 and e = r/9, where h is the elevation of the raised layer, e its thickness and r the mean radius. Their genesis has caused some controversy over the involvement of phenomena such as hydration of anhydrite, or tectonic processes capable of explaining this folding. This paper shows their genesis linked to the dissolution of macrocrystalline gypsum and reprecipitation of microcrystalline gypsum within the same gypsiferous layer. It has been calculated that to reach the theoretical saturation within the few centimetres' thickness of the cap of the tumulus, water infiltration velocities are required of between 0·002 cm s⁻¹ for an uplifted stratum of 2 cm thickness, and 0·03 cm s⁻¹ for 30 cm thickness. These velocities imply the existence of very slow rates of infiltration and/or capillary movement of water within the gypsiferous layer. The secondary microcrystalline gypsum is precipitated in the intercrystalline and intracrystalline voids of the gypsum crystals, producing an increase in porosity and associated volume that causes the doming of the gypsiferous layer. The development of tumuli is a cyclic process which is favoured by a sequence of short wet and dry intervals which, in turn, facilitate the almost simultaneous processes of dissolution and precipitation. These conditions predominate in arid and semiarid climates where intense evaporation can occur suddenly following sporadic infiltration. Copyright © 1999 John Wiley & Sons, Ltd.