Lightning Spectrum Research Articles

Electromagnetic spectrum of lightning from space high-speed shooting analysis to study Schumann resonance

The problem of determining the low-frequency electromagnetic radiation spectrum of lightning activity zones based on the analysis of data obtained from a space-based high-speed camera is investigated. A novel method is proposed for obtaining the electromagnetic spectrum of lightning, based on the hypothesis of the correlation of the time dependences of the radiation intensity of the same lightning discharge, measured in the optical and electromagnetic ranges. The necessity of conducting studies of the influence of local lightning on the processes associated with the Schumann resonance is substantiated.

Study on the Electron Density Measurement of 1 m Rod-plate Gap Discharge Process under the Lightning Impulse

Observation and measurement of the microscopic parameters in the long air gap discharge process play an important role in studying its physical mechanism and the discharge simulation model. In this paper, we combined an electron-multiplying intensified charge-coupled device (EMICCD) camera and a spectrometer, and built a lightning discharge spectrum observation platform of spatiotemporal distribution for the 1 m rod-plane air gap with nanosecond exposure time. The spatiotemporal distributions of the spectral information of the 1 m air gap discharge under positive and negative lightning impulses were obtained. Based on the atomic emission spectroscopy diagnostic method, N and O atomic spectral lines were used to calculate the corresponding electron density at different positions and time points during the breakdown discharges. The testing results were compared with other literature and the differences also were discussed.

Data-Driven Simulations of the Lightning Return Stroke Channel Properties

Accurate estimates of the lightning channel plasma properties are crucial for quantifying the impacts of lightning in the atmosphere and on man-made structures. Gas dynamics models of the return stroke help provide a fundamental understanding of the transformation that occurs in an air parcel subject to the lightning current, yielding quantitative estimates of important channel properties, such as its radius, temperature, and energy deposition. However, until very recently, there was no dataset available in the literature that permitted proper validation of such simulation techniques. This knowledge gap was closed recently when high-speed optical spectra of triggered lightning were made available. In this article, we use measurements to drive and constrain simulations with a gas dynamic model. The model employs a number of parameterizations that allow us to rewrite the hydrodynamic problem as a set of ordinary differential equations. Comparisons with measured temperature and electron density yield errors of the order of tens of percent. The use of more accurate air-plasma transport coefficients helps improve the agreement with measurements. Additionally, we estimate key channel parameters that are not easily measured. The calculated channel radius, resistance, and deposited energy agree well with what has been previously reported in the literature.

A spectral comparison of lightning discharge plasma and laser-induced air plasma

The high time-resolved spectrum of natural lightning is obtained by a slitless spectrograph. The spectrum of natural lightning is compared to the spectrum of laser-induced air plasma. The results show that the spectra of lightning and the spectra of laser-induced air plasma are similar, but they also have some differences. In the superimposed spectrum of lightning, the intensities of atomic lines are far stronger than those of ionic lines, and the continuous spectrum in the whole wavelength region is very strong. However, in the spectrum of laser-induced air plasma, the intensities of atomic lines are similar to those of ionic lines, and there is almost no continuous spectrum in the near-infrared region. In addition, the Hα line is strong in the lightning spectrum but very weak in the spectrum of laser-induced air plasma. The temperature, electron density, and conductivity are calculated, and their evolution with time is also given. The differences in the three physical parameters between lightning and laser-induced air plasma are analyzed. In addition, the reasons of spectral differences have been explained. These results will provide an important reference for the simulation of the lightning spectrum.

Effects of Atmospheric Attenuation on the Lightning Spectrum

AbstractSpectrum carries important information reflecting atomic and molecular processes inside a light source. Accurate spectral diagnosis is vital in revealing the microscopic physical mechanism of the lightning discharge process. Spectral correction was applied considering the influence of atmospheric attenuation, grating efficiency, and camera response on the observed spectrum, thereby solving the problems of atmospheric attenuation in long‐distance lightning spectrum observations. Based on the restored spectrum, the temperature of the lightning return stroke channel was calculated by the ionic and atomic lines respectively. The result showed that corrected temperature at the initial stage of the return stroke, calculated by the ionic line, could reach up to 40,000 K, which was about 10,000 K higher than the values directly obtained from the observed spectrum. Atmospheric attenuation of the atomic spectral line in the near‐infrared band is relatively weak; therefore, atmospheric attenuation was inferred to have a relatively less effect on the channel temperature that was calculated by the atomic spectral lines. This work provided the attenuation ratio of the characteristic lines in lightning spectra with distance, and can used for more precisely quantitative investigation on the physical characteristics of the lightning process. It also has application value for improving the spectral diagnostic techniques on celestial body and other natural luminous process.

Optical Emission Spectroscopy of Lightning Impulse Discharges in Long Air Gaps with and without Water Mist

This work aims to study the various parameters of LI (lightning impulse) discharge channels in an air gap, i.e., the reactive radicals, electron density and channel temperature, and the influence of water mist on the reactive radicals, electron density and channel temperature of the discharge using optical emission spectroscopy. During a LI discharge in air, the gas in the air becomes highly ionized, and the spectra of which are similar to reference spectra of natural lightning. The electron density and channel temperature of the discharges in air under a LI voltage is ca. 3×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">23</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> and ca. 13,000 K, respectively, both of which are lower than those of natural lightning. Compared with LI discharges in air, more OH and OH <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> radicals are detected when the discharge takes place in a water mist-air mixture, indicating the partial decomposition of water molecules on the surface of water droplets during the LI discharge. The addition of water mist results in an 8.8-10.7% lower electron density than during LI discharges in air. However, the addition of water mist does not obviously influence the channel temperature of the air discharge.

Simulation for measurement of lightning channel temperature using a dual-band high-precision lightning imaging spectrometer.

A dual-band high-precision lightning imaging spectrometer (DHLIS) is designed to capture the fine spectrum of transient lightning. DHLIS improves the theoretical spectral resolution limit to 10-3nm and broadens the spectral range to 30-40 nm by employing double echelle gratings in the arms of a spatial heterodyne spectrometer. Four strong and three fine spectral lines are selected to retrieve the temperature of the lightning channel using the Boltzmann plot method. The experimental results indicate that the inversion accuracy of the temperature obtained by inserting fine spectral lines is higher than that by implementation of four strong spectral lines.

Triggered Lightning Spectroscopy: 2. A Quantitative Analysis

AbstractIn the mid 1960s, researchers laid the foundation for modern quantitative lightning spectroscopy. They were the first to acquire time‐resolved return stroke spectra and the first to use spectroscopy as a diagnostic technique to characterize the physical properties of the lightning channel (Orville, 1968a, https://doi.org/10.1175/1520-0469(1968)025&lt;0827:AHSTRS&gt;2.0.CO;2, 1968b, https://doi.org/10.1175/1520-0469(1968)025&lt;0839:AHSTRS&gt;2.0.CO;2, 1968c, https://doi.org/10.1175/1520-0469(1968)025&lt;0852:AHSTRS&gt;2.0.CO;2; Salanave, 1961, https://doi.org/10.1126/science.134.3488.1395; Uman, 1966, https://doi.org/10.1109/MSPEC.1966.5217654). Now, almost 50 years later, technology, including high‐speed cameras, volume‐phase holographic gratings, and triggered lightning, has progressed to the point at which new studies in lightning spectroscopy are needed to verify and improve upon past measurements. In this study triggered lightning spectra were recorded at 673 kfps (1.5 μs per frame) with an exposure time of 1.1 μs. Temperature, number density, and pressure on a 1.5‐μs time scale are presented here for a five‐stroke‐triggered lightning flash. The analysis yields temperatures of the return stroke of greater than 40,000 K as well as electron number densities greater than 1019 cm−3 and peak pressures from 20–350 atm, significantly greater than previous studies. The analysis reveals that in the initial microseconds of the return stroke, the physical characteristics within the channel are rapidly changing and that submicrosecond resolution is needed to observe the initial ionized channel in greater detail.

人工触发闪电通道的辐射特性分析

The spectrum of one triggered lightning with time resolution of 20 μs was observed by using the slit-less spectrograph and the current intensity at the channel bottom was obtained, based on which the radiation characteristics of the lightning spectrum under different current intensities were analyzed. The duration of the spectral line was analyzed according to the excitation energy of the spectral line and the change of the channel current. As a result, the spectral lines were divided into three types. Furthermore, mechanisms of the continuous background radiation of short wavelength and long wavelength were analyzed, respectively. The influences of two radiation mechanisms on continuous background radiation attenuation were researched.

Analysis of twisted pair coupling lightning electromagnetic impulse

For the problem of twisted pair coupling lightning electromagnetic impulse, using a combination of test and theory, established a experimental model of twisted pair coupled lightning electromagnetic impulse, get the twisted pair coupling lightning electromagnetic impulse voltage and spectrum charac teristics, test results: (1) The situation of twisted pair link matching resistance (100 Ω): the coupling voltage increases with the addition of the impulse current; Meanwhile, there is not much impact when increase the height of the coupling voltage. (2) The situation of twisted pair link ground electric resistance: the coupling voltage was positively correlated with the ground electric resistance value in the same height; The coupling voltage increases with increasing height when the resistance value remains the same. (3) Spectral characteristics of the coupling voltage: The frequencies are mainly concentrated around the two frequencies of 8 kHz and 2.3 MHz and the magnitude of the coupling voltage is proportional to the ground electric resistance and the impulse current. The experimental results are in good agreement with the theoretical analysis. The results have some guiding significance.

Triggered lightning spectroscopy: Part 1. A qualitative analysis

AbstractThe first high‐speed spectra of triggered lightning have been obtained. During the summers of 2012 and 2013, spectra were recorded at the International Center for Lightning Research and Testing, Camp Blanding, FL. The spectra were recorded with a high‐speed camera with a grism mounted in front of it. The triggered lightning channels observed were generally at low altitude in a region that included the copper wire. Spectral emissions were recorded at each phase: the initial stage, dart leader, return stroke, and continuing current. These spectra are separated into two major regions: soft ultraviolet to visible (3800–6200 Å) and visible to near infrared (6200–8700 Å). The emissions during the initial stage reflect those of a copper wire burn in air. The majority of the emissions are neutral copper. After the initial stage comes the first return stroke which contains no detected molecular emissions; however, it does contain neutral, singly, and doubly ionized nitrogen and oxygen, neutral argon, and neutral hydrogen. Occasionally, before a return stroke, the dart leader coming down the channel will be stepped. During these occasions the leader spectra resemble that of the return stroke but are dimmer and shorter lived. After the initial portion of the return stroke, there are often changes in the luminosity of the spectrum which corresponds with fluctuations in the continuing current. During these “reillumination phases” no singly or doubly ionized lines have been observed to reemerge over the detection threshold, only neutral emission features.

First Spectrum of Ball Lightning

First Spectrum of Ball Lightning

Saturn’s visible lightning, its radio emissions, and the structure of the 2009–2011 lightning storms

Visible lightning on Saturn was first detected by the Cassini camera in 2009 at ∼35° South latitude. We report more lightning observations at ∼35° South later in 2009, and lightning in the 2010–2011 giant lightning storm at ∼35° North. The 2009 lightning is detected on the night side of Saturn in a broadband clear filter. The 2011 lightning is detected on the day side in blue wavelengths only. In other wavelengths the 2011 images lacked sensitivity to detect lightning, which leaves the lightning spectrum unknown.The prominent clouds at the west edge, or the “head” of the 2010–2011 storm periodically spawn large anticyclones, which drift off to the east with a longitude spacing of 10–15° (∼10,000km). The wavy boundary of the storm’s envelope drifts with the anticyclones. The relative vorticity of the anticyclones ranges up to −f/3, where f is the planetary vorticity. The lightning occurs in the diagonal gaps between the large anticyclones. The vorticity of the gaps is cyclonic, and the atmosphere there is clear down to level of the deep clouds. In these respects, the diagonal gaps resemble the jovian belts, which are the principal sites of jovian lightning.The size of the flash-illuminated cloud tops is similar to previous detections, with diameter ∼200km. This suggests that all lightning on Saturn is generated at similar depths, ∼125–250km below the cloud tops, probably in the water clouds. Optical energies of individual flashes for both southern storms and the giant storm range up to 8×109J, which is larger than the previous 2009 equinox estimate of 1.7×109J. Cassini radio measurements at 1–16MHz suggest that, assuming lightning radio emissions range up to 10GHz, lightning radio energies are of the same order of magnitude as the optical energies.Southern storms flash at a rate ∼1–2per minute. The 2011 storm flashes hundreds of times more often, ∼5times per second, and produces ∼1010W of optical power. Based on this power, the storm’s total convective power is of the order 1017W, which is uncertain by at least an order of magnitude, and probably is underestimated. This power is similar to Saturn’s global internal power radiated to space. It suggests that storms like the 2010–2011 giant storm are important players in Saturn’s cooling and thermal evolution.

VLF wave intensity in the plasmasphere due to tropospheric lightning

AbstractA climatology of VLF (very low frequency) wave intensity from lightning in the plasmasphere is constructed. Starting from Optical Transient Detector/Lightning Imaging Sensor (OTD/LIS) lightning data representing 1995–2005, a climatology of strikes is assembled with 1° × 1° latitude‐longitude spatial resolution, averaged into 2 h bins for each month of the year. Assuming a linear relationship between optical flash rate and VLF power flux, and that the VLF amplitude drops off as one over distance, a proxy for VLF power is developed. A typical lightning spectrum is applied and the values are scaled by appropriate transionospheric absorptions for each time and place. These values are mapped along geomagnetic field lines in order to compare them to E‐field spectral densities measured by the DEMETER satellite between 2005 and 2009. An overview of the DEMETER survey mode data is presented which leads to the best scaling of the lightning VLF climatology in LEO (low earth orbit). The resulting data set represents a monthly, 2‐hour, solar minimum climatology of VLF wave intensity from lightning in LEO. Finally, the E‐field spectral densities are converted to Poynting flux, mapped to the plasmasphere, and converted to B‐field spectral densities. Good overall agreement is found with previous observations and estimates. This new climatology is expected to have a significant impact on calculations of pitch‐angle diffusion for relativistic electrons in the inner radiation belt.

Study of the transport parameters of cloud lightning plasmas

Three spectra of cloud lightning have been acquired in Tibet (China) using a slitless grating spectrograph. The electrical conductivity, the electron thermal conductivity, and the electron thermal diffusivity of the cloud lightning, for the first time, are calculated by applying the transport theory of air plasma. In addition, we investigate the change behaviors of parameters (the temperature, the electron density, the electrical conductivity, the electron thermal conductivity, and the electron thermal diffusivity) in one of the cloud lightning channels. The result shows that these parameters decrease slightly along developing direction of the cloud lightning channel. Moreover, they represent similar sudden change behavior in tortuous positions and the branch of the cloud lightning channel.

Particle Densities and Distributions in Cloud Lightning Channels

AbstractAccording to the plasma theories, the temperature and electron density are calculated based on the wavelengths, relative intensities and transition parameters of lines in cloud lightning spectra which have been obtained on the Tibetan plateau. By using Saha equations, electric charge conservation equations and particle conservation equations, the particle densities in every ionized‐state, the mass density, pressure and the average ionizability of discharge channel are obtained. Moreover, the characteristics of particle distributions in each discharge channel are analyzed. The results show that cloud lightning channels are almost completely ionized, and the most particles are singly ionized while NII has the highest particle density. In general, the particle densities and relative concentrations of different channel positions also have positive correlations with temperatures except for NII, OII and ArII, of which relative concentrations show tiny tendencies of becoming low along with the temperature increasing. Differing from cloud‐to‐ground lightning, the particle densities of different positions along the same cloud discharge channel change in a bigger range but show no regularities. The pressures of channels change from a few tenths of one MPa to several MPa.

The spectra and temperature of cloud lightning discharge channel

Spectra of seven cloud lightning discharges are reported for the first time after captured with a Slit-less Spectrograph on Chinese Tibet Plateau. The structural characters are analyzed and compared with the spectra of cloud-to-ground lightning, and the results indicate that the spectra of cloud lightning show two different kinds of structure characteristics. One has the similar structure as those of cloud-toground lightning discharge, and the other is absolutely different. Meanwhile, more lines of OII with high excited energy are recorded in the spectra of cloud lightning discharge in comparison with that of cloud-to-ground lighting happening in the same region. Temperatures at different positions are calculated and temperature characteristics of these two sorts are analyzed, based to the wavelength, relative intensities and other transition parameters. We suggest that the physical process in the cloud discharge channels changes with much more rapid velocity and wider range compared to cloud-to-ground lightning. The differences between the two types of cloud discharge also reflect some discrepancies between the discharge characteristics.

Lightning on Jupiter observed in the [formula omitted] line by the Cassini imaging science subsystem

Night side images of Jupiter taken by the Cassini Imaging Science Subsystem (ISS) camera with the H α filter reveal four lightning clusters; two of them are repeated observations of the same storm. All of these flashes are associated with storm clouds seen a few hours earlier on the day side of Jupiter. Some of the clouds associated with lightning do not extend to the upper troposphere. The repeated lightning observations taken 20 hr apart show that storm clouds, whose mean lifetime is ∼4 days, are electrically active during a large fraction of their lifetime. The optical power of the lightning detected with the H α filter compared to the clear-filter power of Galileo lightning may indicate that the H α line in the lightning spectrum is about ten times weaker than expected, consistent with a flat spectrum having no prominent H α line. This may suggest that lightning is generated in atmospheric layers deeper than 5 bars. This, in turn, may suggest that the water abundance of the jovian interior is more than 1 × solar. Averaged over many flashes, the most powerful Cassini lightning storm emits 0.8 × 10 9 W in the H α line, which implies 4 × 10 10 W of broadband optical power. This is 10 times more powerful than the most intense jovian lightning observed before by Voyager 2.

A model of the lightning discharge at Jupiter

Based on the lightning waveform and spectra observed by the Galileo Atmospheric Probe, we present a discharge, radiation, and propagation model of the Jovian lightning that explains the absence of detectable HF spherics along with the measurement of ELF whistler emissions by the Voyager radio and plasma wave instruments. We find that although there is signal attenuation in the ionosphere, the controlling factor in determining lightning detectability at Jupiter is the intrinsically slow nature of the lightning discharge itself. The proposed discharge model is not unique, but matches the observed spectrum which spans several frequency decades and provides a basis for comparing lightning discharge models for other planets.

Spectral Irradiance Measurements of Simulated Lightning in Planetary Atmospheres

Measurements of the spectral irradiance from approximately 380 to 820 nm are reported for laboratory simulations of lightning in the atmospheres of Venus, Jupiter, and Titan. The observations were made at 1 and 5 bars of pressure for Venus and Jupiter and at 1 bar for the Titan mixture. The spectra were obtained by observing laser-induced plasmas with a scanning spectrometer and an optical multichannel analyzer. Simulations of lightning show that atomic line and continuum radiation dominate the spectra. Weak molecular band radiation from CN was also observed for Venus and Titan. As the ambient pressure was increased from 1 to 5 bars, the prominence of the line radiation diminishes compared to the continuum radiation, some lines disappear, and the intensity of the molecular band radiation increases. Laboratory results for the venusian lightning spectrum are consistent with those found by the Venera 9 spectrometer when it viewed a storm on the nightside of Venus. For both Jupiter and Venus, narrow spectral features are present that are ideal for detecting lightning from Earth-based telescopes.