Impulsive Coupling Between the Atmosphere and Ionosphere/Magnetosphere

This review covers various aspects of the impulsive coupling in the ULF frequency range between atmospheric discharge processes and upper ionosphere. Characteristic feature of the upper ionosphere is the occurrence of the ionospheric Alfven resonator (IAR) and MHD waveguide, which can trap the electromagnetic wave energy in the range from fractions of Hz to few Hz. Induction magnetometer observations at mid-latitude stations are considered as an example of a transient ULF response to the regional and global lightning activity. For many events, besides the main impulse produced by a lightning discharge, a secondary impulse delayed about 1 sec was observed. These secondary echo-impulses are probably caused by the partial reflection of wave energy of the initial lightning pulse from the upper IAR boundary in the topside ionosphere. The multi-band spectral resonant structure (SRS) can be formed owing to the occurrence of paired pulses in analyzed time series. The statistical superposed epoch method indeed has revealed a dominance of two-pulse structure in the magnetic field background during the periods of the SRS occurrence. The numerical modeling shows that during the lightning discharge a coupled wave system comprising IAR and MHD waveguide is excited. In the lightning proximity (about few hundred km) the amplitudes of radial component is 1–2 orders less than those of the azimuthal component, and only the lowest IAR harmonics are revealed in the radial magnetic component. At distances ～10³?km the spectral power densities of both components are comparable, and the SRS is more pronounced. The problems and further prospects of the study of the impulsive magnetosphere–ionosphere–atmosphere coupling via transient processes during thunderstorms are discussed.     

飞机复合材料表面导电层的雷击仿真研究

复合材料在飞机上的应用越来越广泛,与金属相比复合材料导电性较差,因此处于雷击区域的复合材料部件表面要设计导电防护层以承受雷击时的瞬间放电,避免复合材料部件的烧蚀损伤。本研究利用数值仿真的方法建立了数学模型,计算了复合材料表面导电层通过雷击电流脉冲后的电场和温度场分布,并对该导电层的雷击防护能力及可靠性进行了评价。模拟结果表明,厚度为0.20 mm的铝导电层最适宜做飞机表面的雷击防护层。     

Controlled VLF wave injection experiments in the magnetosphere

Whistler-mode waves injected into the magnetosphere from ground sources (e.g., lightning discharge, vlf transmitters) are used to probe the distribution of ions and electrons in the magnetosphere. They also cause wave growth (vlf emissions) and precipitation of electrons. Bursts of X-rays (> 30 keV) and enhancements of D-region ionization are examples of precipitation effects caused by lightning-generated waves. Growing narrowband wave trains are triggered by manmade coherent waves. Growth rates of 100 dB s^-1 and total growths up to 30 dB have been measured using 5.5 kHz signals transmitted from Siple Station, Antarctica. Another source of coherent wave input to the magnetosphere are the harmonics from commercial power line systems. Power line harmonic radiation may suppress triggered emissions or change their frequency-time slope. Exponential growth of narrowband emissions is explained in terms of cyclotron resonance between the waves and trapped energetic electrons, with feedback included. Applications of wave injection experiments include: (1) study of emission mechanisms, (2) control of energetic particle precipitation, (3) diagnostics of cold and hot plasma, and (4) vlf communications.     

Thermal damage analysis of aircraft composite laminate suffered from lightning swept stroke and arc propagation

Lightning strike is a complicated process involving multi-field coupling. In order to investigate the thermal damage mechanism of carbon fiber reinforced composites subject to lightning swept stroke, a complete numerical method is presented. Numerical model of lightning discharge is established based on Magneto Hydro Dynamics (MHD) and calculated by FLUENT secondary development technology. Considering aerodynamic flow effect, channel formation and evolution process during lightning discharge is analyzed for lightning current waveform A. Thermal-electric Coupling model is presented according to Radial Basis Function (RBF) interpolation theory, which is implemented by compiling program to make lightning current and heat energy inject into composite laminate. Consequently, damage mechanism of composite laminate under lightning swept stroke is studied based on the coupled numerical model and element deletion method. Ablation damage morphology of composite laminate is analyzed to understand plasma expansion and reattachment in arc root. The results show that aerodynamic flow makes the lightning channel move fast and composite laminate is deteriorated due to thermal damage.     

Physical Processes Related to Discharges in Planetary Atmospheres

This paper focuses on the rudimentary principles of discharge physics. The kinetic theory of electron transport in gases relevant to planetary atmospheres is examined and results of detailed Boltzmann kinetic calculations are presented for a range of applied electric fields. Comparisons against experimental swarm data are made. Both conventional breakdown and runaway breakdown are covered in detail. The phenomena of transient luminous events (TLEs), particularly sprites, and terrestrial gamma-ray flashes (TGFs) are discussed briefly as examples of discharges that occur in the terrestrial environment. The observations of terrestrial lightning that exist across the electromagnetic spectrum and presented throughout this volume fit well with the broader understanding of discharge physics that we present in this paper. We hope that this material provides the foundation on which explorations in search of discharge processes on other planets can be based and previous evidence confirmed or refuted.     

Lightning Related Transient Luminous Events at High Altitude in the Earth’s Atmosphere: Phenomenology, Mechanisms and Effects

This paper presents a literature survey on the recent developments related to experimental and modeling studies of transient luminous events (TLEs) in the middle atmosphere termed elves, sprites and jets that are produced in association with thunderstorm activity at tropospheric altitudes. The primary emphasis is placed on publications that appeared in refereed literature starting from year 2008 and up to the present date. The survey covers general phenomenology of TLEs and their relationships to characteristics of individual thunderstorms and lightning, physical mechanisms and modeling of TLEs, past, present and future orbital observations of TLEs, and their chemical, energetic and electric effects on local and global scales.     

Venus lightning

Although it is not unanimously accepted, many independent observations lead to the conclusion that lightning is prevalent on Venus. The electromagnetic signals detected by all 4 Venera landers are most readily explained as generation by lightning. The Venera 9 spectrometer appears to have observed a lightning storm on one occasion. The Pioneer Venus plasma wave instrument detects waves both below the electron gyrofrequency that may be due to lightning and signals above the electron gyrofrequency but at very low altitudes that may be due to the near field of the lightning. The VLF observations suggest that Venus lightning must be an intra-cloud phenomenon which is most frequent in the afternoon and evening sector. The occurrence rate is likely to be greater than on Earth.     

A Review of Low Frequency Electromagnetic Wave Phenomena Related to Tropospheric-Ionospheric Coupling Mechanisms

Investigation of coupling mechanisms between the troposphere and the ionosphere requires a multidisciplinary approach involving several branches of atmospheric sciences, from meteorology, atmospheric chemistry, and fulminology to aeronomy, plasma physics, and space weather. In this work, we review low frequency electromagnetic wave observations in the Earth-ionosphere cavity from a troposphere-ionosphere coupling perspective. We discuss electromagnetic wave generation, propagation, and resonance phenomena, considering atmospheric, ionospheric and magnetospheric sources, from lightning and transient luminous events at low altitude to Alfvén waves and particle precipitation related to solar and magnetospheric processes. We review ionospheric processes as well as surface and space weather phenomena that drive the coupling between the troposphere and the ionosphere. Effects of aerosols, water vapor distribution, thermodynamic parameters, and cloud charge separation and electrification processes on atmospheric electricity and electromagnetic waves are reviewed. Regarding the role of the lower boundary of the cavity, we review transient surface phenomena, including seismic activity, earthquakes, volcanic processes and dust electrification. The role of surface perturbations and atmospheric gravity waves in ionospheric dynamics is also briefly addressed. We summarize analytical and numerical tools and techniques to model low frequency electromagnetic wave propagation and to solve inverse problems and outline in a final section a few challenging subjects that are important to advance our understanding of tropospheric-ionospheric coupling.     

磁激等离子体超声速气流的瞬态加速系统及其实验研究

研制了基于激波风洞的热电离系统,设计了马赫数Ma=1.5的喷管和分段法拉第型实验段,并选用了合理的磁场及电场方案。采用氦气驱动氩气模式,通过在激波管低压段注入电离种子K₂CO₃粉末实现气流的热电离;压缩后的高温氩气启动喷管,以瞬态超声速导电流体形式通过实验段。实验结果表明:当激波管高压段压力为1.1 MPa、低压段压力为500 Pa时,喷管出口的超声速导电气流温度约为4 185.91 K,压力约为0.037 MPa;当电容电压为400 V、磁感应强度为1.0 T时,由实验段中间位置电极的放电特性可以估算出气流电导率约为78.1 S/m,单对电极输入功率约为9.46 kW;用感应电压法对加速效果进行初步评估,出口气流速度增加了29.3%,电效率为26.1%。     

Lightning Detection by LAC Onboard the Japanese Venus Climate Orbiter, Planet-C

Lightning activity in Venus has been a mystery for a long period, although many studies based on observations both by spacecraft and by ground-based telescope have been carried out. This situation may be attributed to the ambiguity of these evidential measurements. In order to conclude this controversial subject, we are developing a new type of lightning detector, LAC (Lightning and Airglow Camera), which will be onboard Planet-C (Venus Climate Orbiter: VCO). Planet-C will be launched in 2010 by JAXA. To distinguish an optical lightning flash from other pulsing noises, high-speed sampling at 50 kHz for each pixel, that enables us to investigate the time variation of each lightning flash phenomenon, is adopted. On the other hand, spatial resolution is not the first priority. For this purpose we developed a new type of APD (avalanche photo diode) array with a format of 8×8. A narrow band interference filter at wavelength of 777.4 nm (OI), which is the expected lightning color based on laboratory discharge experiment, is chosen for lightning measurement. LAC detects lightning flash with an optical intensity of average of Earth’s lightning or less at a distance of 3 Rv. In this paper, firstly we describe the background of the Venus lightning study to locate our spacecraft project, and then introduce the mission details.     

飞机雷电防护设计与鉴定试验

飞机遭受雷击后产生强大的雷电流,它严重的威胁飞行的安全.本文分析了雷电造成的危害,并论述了飞机结构设计应为雷电流提供低阻抗的通路.对雷击放电敏感的部位和部件,必须根据自身的重要性采取适当的雷电防护措施,以尽可能减少雷电对飞机的损害.最后介绍了为确保雷电防护措施的可靠性而进行的验证试验方法.     

An Overview of Earth’s Global Electric Circuit and Atmospheric Conductivity

The Earth’s global atmospheric electric circuit depends on the upper and lower atmospheric boundaries formed by the ionosphere and the planetary surface. Thunderstorms and electrified rain clouds drive a DC current (～1 kA) around the circuit, with the current carried by molecular cluster ions; lightning phenomena drive the AC global circuit. The Earth’s near-surface conductivity ranges from 10^?7 S?m^?1 (for poorly conducting rocks) to 10^?2 S?m^?1 (for clay or wet limestone), with a mean value of 3.2 S?m^?1 for the ocean. Air conductivity inside a thundercloud, and in fair weather regions, depends on location (especially geomagnetic latitude), aerosol pollution and height, and varies from ～10^?14 S?m^?1 just above the surface to 10^?7 S?m^?1 in the ionosphere at ～80 km altitude. Ionospheric conductivity is a tensor quantity due to the geomagnetic field, and is determined by parameters such as electron density and electron–neutral particle collision frequency. In the current source regions, point discharge (coronal) currents play an important role below electrified clouds; the solar wind-magnetosphere dynamo and the unipolar dynamo due to the terrestrial rotating dipole moment also apply atmospheric potential differences. Detailed measurements made near the Earth’s surface show that Ohm’s law relates the vertical electric field and current density to air conductivity. Stratospheric balloon measurements launched from Antarctica confirm that the downward current density is ～1 pA m^?2 under fair weather conditions. Fortuitously, a Solar Energetic Particle (SEP) event arrived at Earth during one such balloon flight, changing the observed atmospheric conductivity and electric fields markedly. Recent modelling considers lightning discharge effects on the ionosphere’s electric potential (～+250 kV with respect to the Earth’s surface) and hence on the fair weather potential gradient (typically ～130 V?m^?1 close to the Earth’s surface. We conclude that cloud-to-ground (CG) lightning discharges make only a small contribution to the ionospheric potential, and that sprites (namely, upward lightning above energetic thunderstorms) only affect the global circuit in a miniscule way. We also investigate the effects of mesoscale convective systems on the global circuit.     

Ground-Based and Space-Based Radio Observations of Planetary Lightning

We review radio detection of planetary lightning performed by Voyager, Galileo (including in-situ probe measurements), Cassini, and other spacecraft, and compare the information on the underlying physics derived from these observations—especially the discharge duration, at Jupiter and Saturn—with our knowledge of terrestrial lightning. The controversial evidence at Venus is discussed, as well as the prospects for lightning-like discharges in Martian dust-storms (and studies on terrestrial analogues). In addition, lightning sources provide radio beacons that allow us to probe planetary ionospheres. Ground-based observations of Saturn’s lightning have been attempted several times in the past and have been recently successful. They will be the subject of observations by the new generation of giant radio arrays. We review past results and future studies, focussing on the detection challenges and on the interest of ground-based radio monitoring, in conjunction with spacecraft observations or in standalone mode.     

飞机雷电防护

雷电是一种危险现象,但是到目前为止还没有一种技术能够防止飞机遭受雷击。本文分析了雷电造成的危害,并论述了飞机结构设计应该为雷电流提供低阻抗的通路。对于对雷击放电敏感的部位和部件,必须根据其自身的重要性采取适当的雷电防护措施,以尽可能减少雷电对飞机的损害。最后介绍了为确保雷电防护措施的可靠性而进行的验证试验方法。     

Plasma waves at Venus

Many significant wave phenomena have been discovered at Venus with the plasma wave instrument flow on the Pioneer Venus Orbiter. It has been shown that whistler-mode waves in the magnetosheath of the planet may be an important source of energy for the topside ionosphere. Plasma waves are also associated with thickening of the ionopause current layer. Current-generated waves in plasma clouds may provide anomalous resistance resulting in electron acceleration, possibly producing aurora. Ion-acoustic waves are observed in the bow shock, and appear to be a feature of the magnetotail boundary. Lastly plasma waves have been cited as evidence for lightning on Venus.     

复合材料层合板雷击烧蚀损伤模拟

 为解决复合材料层合板的雷击烧蚀问题,通过复合材料层合板雷电流烧蚀的热-电-结构耦合分析,建立复合材料层合板烧蚀的三维有限元模型。利用删除单元法模拟复合材料层合板在不同脉冲波形雷电流作用下的冲击响应,进行复合材料层合板雷击损伤机理和损伤模式分析,得出了复合材料层合板在不同脉冲波形和峰值雷电流作用下的瞬态热传递和热烧蚀规律。分析了不同雷电流参数对烧蚀结果的影响。结果表明峰值电流、放电量和比能对复合材料层合板的烧蚀尺寸和内部损伤产生很大的影响。     

The menagerie of geospace plasma waves

Sounding rockets and satellites have discovered a large variety of plasma waves within the Earth's magnetosphere—geospace. These waves are found over a frequency range of millihertz to megahertz. The frequency ranges are generally associated with characteristic frequencies such as the plasma frequency and gyrofrequency. Most waves are generated by hot or streaming magnetospheric plasma; some waves are due to lightning discharges, to intentional man-made transmitters or to incidental radiation from power transmission systems. Propagation of waves from the observation region back to a probable source region can be modelled using ray tracing techniques in a model magnetosphere where the electron number density, ion composition and magnetic field vector is specified. Information in addition to the common amplitude-frequency-time spectrograms can be obtained from the received waves using multiple antennas and receivers. Cross-correlation of the wave electric and magnetic components can provide information on the wave polarization and direction of propagation and on the wave distribution function.     

全权限数字电子控制器雷电试验方法研究

在分析机载设备雷电感应敏感度试验相关标准的基础上,对全权限数字电子控制器雷电间接效应试验方法进行研究。对雷电间接效应耦合方式进行了分类,并以某型全权限数字电子控制器为例,介绍了数字电子控制器雷电感应瞬态敏感度试验波形组、试验电平选择方法及试验过程。并对空客和波音公司机载设备雷电感应瞬态敏感度试验方法做了初步介绍。研究成果可供制定机载设备雷电防护要求及试验方案时参考。     

雷击建筑物时防雷系统中雷电流的分布研究

主要讨论雷直击建筑物时雷电流在防雷系统中的分布特性，介绍利用计算机进行数值计算的方法。通过典型算例、传统的电磁暂态计算程序——EMTP的计算结果和利用清华大学高压实验室的冲击大电流发生装置，对此结构模型进行模拟试验，将3种结果进行比较，从而验证了本研究所编制的计算机程序的正确性。为进一步研究室内电磁场的暂态分析做好基础。     

Discharges in the Stratosphere and Mesosphere

In the present paper salient features of discharges in the stratosphere and mesosphere (namely sprites, halos, blue starters, blue jets, gigantic jets and elves), are discussed. The electrostatic field due to charge imbalance during lightning processes may lead to stratospheric/mesospheric discharges either through the conventional breakdown based on streamers and leaders or relativistic runaway mechanism. Most (not all) of the observed features of sprites, halos and jets are explained by this processes. Development and evolution of streamers are based on the local transient electrostatic field and available ambient electron density which dictate better probability in favor of positive cloud-to-ground discharges, and thus explains the polarity asymmetry in triggering sprites and streamers. Elves are generated by electromagnetic pulse radiated by return stroke currents of cloud-to-ground/inter-cloud discharges. Generation of the both donut and pancake shape elves are explained. Electrodynamic features of thunderstorms associated with stratospheric/mesospheric discharges are summarized including current and charge moment associated with relevant cloud-to-ground discharges. The hypothesis relating tropospheric generated gravity waves and mesospheric discharges are also discussed. Finally some interesting problems are listed.