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One of the most enigmatic types of sprites is the dancing sprite which appears to dance above the storm as sequential luminous emissions a few 100 ms or less apart. Dancing sprites occur in relatively small proportion and many aspects of their generation remain unknown. We present a multi‐instrumental analysis of a 20‐hr duration Mesoscale Convective System (MCS) over the northwestern Mediterranean Sea on September 21, 2019, that produced 21 sprites recorded with a video camera, of which 19 (90%) were dancing sprites. The asymmetric trailing stratiform MCS developed in strong convective conditions having a CAPE of 3,500 J kg−1. It formed several convective cores (up to 2,900 km2 with cloud top temperature <−66°C) and exhibited a bow echo structure during the sprite production period. Using Lightning Mapping Array data, we show that the sprite producing positive cloud‐to‐ground (SP + CG) flashes mainly initiated at the edge of the convective line on the side of the stratiform region. The flashes propagated 100–200 km across it, producing both positive and negative CG strokes. The 19 dancing sprite events included 49 sequences, of which 46 were associated with distinct SP + CG strokes and 3 with surges during the continuing current. An especially bright and wide sprite sequence was produced by three distinct SP + CG strokes that occurred within 3 ms and spread over 54 km. This sprite sequence could be classified as a new sprite category resembling a "wall" but structured in three groups, each associated with one of the +CG strokes. Plain Language Summary: One of the most enigmatic types of sprites is the dancing sprite which appears to dance above the storm as sequential luminous emissions a few 100 ms or less apart. Dancing sprites occur in relatively small proportion and many aspects of their generation remain unknown. We present a multi‐instrumental analysis of a 20‐hr duration Mesoscale Convective System over the Mediterranean Sea on September 21, 2019, that produced 21 sprites, of which 19 were dancing. The storm developed in strong convective conditions and formed several convective cores with very high cloud‐tops and a bow‐echo structure. Most of the sprite producing flashes propagated from the convective to the stratiform region over long distances producing strokes of both polarity. The 19 events included 49 sprite sequences, of which 46 were associated with distinct strokes and 3 with surges during the continuing current. An especially bright and wide sprite was produced by three strokes that occurred within 3 ms and separated by 54 km and could be classified as a new sprite category. We accredit the high proportion of dancing sprites to a complex charge structure in the stratiform region with large potential and pockets of charge driving the leaders and allowing substantial discharge. Key Points: A high percentage (90%) of dancing sprites were produced by a large asymmetric MCS which developed in strong convective conditions over the Mediterranean SeaThe sprite parent flashes mainly initiated at the edge of the convective region and propagated 100–200 km across the stratiform regionAn especially bright and wide sprite sequence was produced by three distinct positive CG strokes that occurred within 3 ms and were separated by 54 km [ABSTRACT FROM AUTHOR]

On June 2 and 3, 2019, 63 sprites were captured from Langmuir Laboratory in central New Mexico. The two storms investigated were located in northwest Texas, 400–800 km away from the observation site. Optical recordings were made with a Phantom V2010 camera operating at up to 100,000 frames per second. Electromagnetic remote sensing of lightning and sprite electric fields was performed with a sensitive slow antenna (LEFA). Data from the Earth Networks Total Lightning Network (ENTLN) were used to locate the sprite parent flashes. The combined information of these three data sets reveals that a staggering fraction of more than half of the sprites observed have a distinguishable electromagnetic signature attributed to currents flowing within the sprite body. Furthermore, these sprite current signatures were unusually large in comparison to previous reports. The sprite electric field changes have roughly half the amplitude of their parent lightning flash's, corresponding to sprite peak currents of 26–58 kA on average. The largest sprites have current moments of up to 2,700 kAkm, as inferred from a computationally efficient method to solve Maxwell's equations. Detailed comparison between the sprites' electromagnetic signatures and high-speed optical recordings show that optically large sprites containing upward streamers (carrots and jellyfish) tend to have larger electrical currents than the ones displaying only downward streamer development (column sprites). Finally, a clear increasing trend in peak current moment is evident with increasing morphological complexity, from columns to carrots to jellyfish sprites. [ABSTRACT FROM AUTHOR]

We report the first observation of an unusual red sprite produced by negative cloud‐to‐ground (CG) lightning from the Imager of Sprites and Upper Atmospheric Lightning (ISUAL) in Colombia on August 15, 2012. The impulse charge moment change for this event is approximately −520 C·km, barely reaching the threshold for negative sprite production. However, different from all previously reported observations, this negative sprite contains a distinct "sprite current" feature that is unambiguously identified in the very‐low‐frequency magnetic field recorded at the 3,387 km range in Duke Forest. There is no evidence that this feature was produced by a fast discharging process associated with the causative CG stroke. Instead, the sprite current signal corresponds well to high‐altitude optical emissions associated with the charge flow in the sprite body. The charge moment change caused by the charge transfer in the sprite region was estimated to be about −460 C·km. We attempt to reveal the possible causes of this atypical event from the perspective of the parent thunderstorm and the local ionosphere irregularities, whereas we believe that the most possible reason remains to lie in an extraordinarily long duration (more than 5 ms) of charge transfer to ground following the return stroke. Plain Language Summary: Although the sprite observations associated with negative cloud‐to‐ground (CG) strokes are very rare, the analyses on limited cases still yield a consensus on the typical features of negative sprites. Negative sprites have not yet been reported to contain the "sprite current" signature usually detected in bright positive sprites. With the dataset provided by the Imager of Sprites and Upper Atmospheric Lightning, we found an extremely rare case of negative sprite. The associated broadband magnetic field clearly shows the characteristic waveform indicative of sprite current, despite the impulse charge moment change (about −520 C·km) barely exceeding the critical strength for producing negative sprites. Our analyses exclude the possibility that this sprite current signature was produced by the low‐altitude lightning discharges; instead, the absence of low‐frequency emissions during the occurrence of the suspected sprite current strongly suggests that the second slow magnetic pulse was driven by the charge transfer associated with the high‐altitude optical emissions. This exceptional observation implies that there could be some situations (such as local plasma irregularities) hidden in the mesosphere. However, the most likely cause seems to be a particularly long charge transfer time (more than 5 ms) after the return stroke of the parent CG flash. Key Points: First observation of a negative halo/sprite event with the signature of sprite current in the concurrent very‐low‐frequency sferic waveformThis unusual negative sprite is produced by an impulse charge moment change (approximately −520 C·km) barely enough for producing a spriteThe occurrence of this event is likely caused by an extraordinarily long duration of charge transfer to ground following the return stroke [ABSTRACT FROM AUTHOR]

Physical properties of elves, jets and sprites, which are the most interesting types of high-attitude discharges in the atmosphere, are considered in the work. The results of researches of its fractal characteristics are presented. The obtained results give grounds for a deeper insight of development, relaxation of such atmosphere processes and taking into account of their action on radio systems. [ABSTRACT FROM AUTHOR]

The article focuses on sprites, which are short-lived optical phenomena that occur above large thunderstorms. This paper discusses the first ground-based recorded observations of sprites from South Africa. It is mentioned that in 2 observations nearly 100 sprite elements were recorded from Sutherland in the Northern Cape. It is noted that chemical changes caused by sprite could have an impact on the heating or cooling of the area or interfere with long distance communication.

Sprites are a potential thermal infrared radiation source in the stratosphere and mesosphere through molecular vibrational excitation. We developed a plasma‐chemical model to compute the vibrational kinetics induced by a sprite streamer in the 40‐ to 70‐km altitude range until several tens of seconds after the visible flash is over. Then, we computed the consecutive time‐dependent thermal infrared spectra that could be observed from the stratosphere (from a balloon platform), high troposphere (from an aircraft), and low troposphere (aircraft or altitude observatory) using a nonlocal thermodynamic equilibrium radiative transfer model. Our simulations predict a strong production of CO2 in the (001) vibrational level which lasts at least 40 s before falling to background concentrations. This leads to enhanced emissions in the long‐wavelength infrared, around 1,000 cm−1, and midwavelength infrared, around 2,300 cm−1. The maximum sprite infrared signatures (sprite spectra minus background spectra) reach several 10−7 W/sr/cm2/cm−1 after propagation through the mesosphere and stratosphere, to an observer located at 20–40 km of altitude. This maximum signal is about 1 order of magnitude lower if propagated until the troposphere. From the two spectral bands, the 1,000‐cm−1 one could be detected more easily than the 2,300‐cm−1 one, which is more affected by atmospheric absorption (CO2 self‐trapping at all altitudes and H2O mostly in the troposphere). With a sufficiently sensitive instrumentation, mounted in an open stratospheric balloon platform for example, the 1,000‐cm−1 band could be detected from 20–40 km of altitude. Key Points: Sprite thermal infrared signature could reach up to 10−7 W/sr/cm2/cm−1 for an observer located in the stratosphereThe maximum signal is in the long‐wavelength infrared, around 1,000 cm−1This signature should be detectable from stratospheric balloons [ABSTRACT FROM AUTHOR]

For the first time in > 30 years of routine sampling under the Arctic Monitoring and Assessment Program, a parasite was found in the liver of ringed seals (Phoca hispida) collected near Qaanaaq (Thule), Northwest Greenland, in 2008 and 2014. Concerns regarding changes to parasite occurrence, possibly related to climate change and bioaccumulation of immunomodulating anthropogenic pollutants, spurred further investigations into parasite characterization, and implications for wildlife health and seal hunters. Microscopic, molecular, and morphometric analyses are presented herein. Of 40 seals, 6 (15%) were infected, and 5 of 6 of these seals had severe infections. The parasite was identified morphologically as Orthosplanchnus arcticus Odhner, 1905 (Trematoda; Digenea: Brachycladiidae). Macro- and microscopic pathologic study indicated mild-to-severe biliary hyperplasia associated, stasis associated, and fibrosis associated with trematode infections. Molecular analysis of the trematode confirmed its classification within the Brachycladiidae using sequencing and comparing Internal Transcribed Spacer-1, mitochondrial-NADH Dehydrogenase 3, 18S ribosomal DNA, and Cyclooxygenase-1 regions. This is the first ever report of O. arcticus in ringed seals from Qaanaaq and is one of the most northern records of this parasite. We found significant liver pathology in severely infected seals, but its effects on health of seals in this population are unknown. Host-specificity and the lifecycle of O. arcticus are unknown, but transmission may involve subsistence and commercially harvested Arctic fish species. Further work is needed to answer these questions. Surveying parasites in Arctic wildlife is important in order to assess potential effects on wildlife and human health (i.e., zoonoses). [ABSTRACT FROM AUTHOR]

Results of experiments on high-voltage discharges in air with a pressure gradient are presented. The experiments were carried out at the setup developed at the Institute of Applied Physics, Russian Academy of Sciences. The goal of the experiments was laboratory modeling of high-altitude atmospheric discharges-sprites and jets. The setup and diagnostic techniques are described. The experimental results include the distribution of the gas pressure in the vacuum chamber formed by means of pulsed air puffing, photographs of discharges in air with a pressure gradient, and the dependences of the discharge current and optical emission intensity on the initial conditions. [ABSTRACT FROM AUTHOR]

Transient luminous event (TLEs) observations have been conducted in mainland China since 2007, with a number of TLEs documented. This study analyzed a very unusual and unique positive sprite event, that may be produced jointly by two distinct positive cloud-to-ground lightning flashes (+CGs) occurring within a short time difference but with different locations separated by about 27 km. This observation is different from previous studies reporting that most of the sprites were triggered by a single +CG flash and its possible following continuous current. Detailed analysis on extremely low frequency (ELF) magnetic field shows that combined charge moment change (CMC) due to the two +CGs is smaller (~1478 C km) than those of the parent CGs for the other two sprites (1582 and 2134 C km, respectively) recorded over the same thunderstorm. The vertical extension and brightness of the sprites correspond well with the CMC of their parent CGs, namely, the larger the CMC value the brighter the sprite, and the larger the CMC value the larger the vertical extension. Negative lightning flashes dominated during the thunderstorm life cycle. The three sprites occurred during a time window in which both negative and positive flashes were active. The three sprites occurred over the thunderstorm stratiform region. [ABSTRACT FROM AUTHOR]

This paper reports on the recent developments in spectroimagers for sprite campaigns in Taiwan. We first introduce two types of spectroimagers, the slit and slitless types, and discuss their advantages and shortcomings. Next we explore the instrument development and procedures undertaken for this study. In 2006, a slit spectroimager was installed for a sprite campaign and on 15 August of that year, two sprite spectra were recorded using the slit spectroimager along with seven sprites, one halo, one ELVES emission and two jets. By the end of 2015, a slitless spectroimager had been successfully constructed and was ready to conduct additional investigations. On 7 May 2016, a sprite spectrum was recorded using the slitless spectroimager. Following an examination of the calibrations (comprising detection region field of view, wavelength calibration, and response curve), data analysis, and additional calibrations (comprising elevation and azimuthal angles, atmospheric transmittance, and theoretical wavelength calculations) performed in this study, we present the results from our observed sprite spectra using the slit and slitless spectroimagers. [ABSTRACT FROM AUTHOR]

The Imager of Sprites and Upper Atmospheric Lightning (ISUAL), on board the FORMOSAT-2 satellite launched in 2004, is the first instrument primarily dedicated to transient luminous event (TLE) surveys from space. The ISUAL TLE geolocation accuracy and detection efficiency are validated in this paper through two coordinated observation events using ISUAL and the Taiwan TLE ground campaign, the first coordinated space and ground observations. Due to the long distances between TLEs and the observation stations, triangulation required taking the Earth's curvature into account using spherical trigonometry. After a series of systematic triangulation procedures, the results indicate that the coordinated ISUAL and ground station geolation accuracy is less than 7 km. Moreover, three columniform sprites were recorded at multiple sites during the ground campaign. The triangulation of individual elements shows that the map projection of columniform sprites is nearly circular, parallel and fan shaped. The aforementioned events demonstrate that the columniform sprite distribution patterns are diverse. The average base altitude of the columns is 72.4 ± 2.4 km, and the average terminal altitude is 82.3 ± 1.8 km. The sprite column width is estimated to be < 0.5 km. [ABSTRACT FROM AUTHOR]

The Global Lightning and Sprite Measurements on the Japanese Experiment Module (JEM-GLIMS) started continuous nadir observations of lightning and transient luminous events (TLEs) at the International Space Station (ISS) in November 2012 and completed the observations in August 2015. As JEM-GLIMS uses the nadir observation technique, the JEM-GLIMS optical instruments simultaneously measure both incomparably intense lightning emissions and weak sprite emissions. We adopted combined data analytical methods to distinguish between these two types of emissions: (1) a subtraction of the wideband LSI-1 image from the narrowband LSI-2 image, (2) a calculation of the intensity ratio between different photometer channels, and (3) an estimation of the charge moment change (CMC) of the suspected sprite-producing CG discharge. This report presents as a case study one sprite event detected at 19:50:40.30580 UT on 28 September 2013 and identified using the above analytical methods. From the results derived from detailed data analyses, we judged that the optical emission measured by LSI-2 is a sprite emission. We carried out the geometry conversion toward the LSI-1 and subtracted images and found that the sprite emission location shifts by 3.5 km from the peak lightning emission location, which agree with the previous reports. The detailed horizontal distributions of sprites and the relationship between the sprite location and the parent lightning location are quantitatively revealed for the first time. [ABSTRACT FROM AUTHOR]

We examined the broadband (< 1 Hz to 30 kHz) lightning sferics associated with 395 sprites observed near North America by the Imager of Sprites and Upper Atmospheric Lightning (ISUAL) onboard the FORMOSAT-2 satellite in a 12-year period from 2004 - 2015. Our analysis indicates that the ISUAL dataset contains a significant fraction (69, or ~18%) of negative sprites, which were predominantly (> 80%) observed over oceanic and coastal thunderstorms mostly in tropical areas. The mean and median of impulse charge moment change (iCMC) associated with positive (negative) sprites are +346 C km (-709 C km) and +280 C km (-649 C km), respectively. The morphology and parent lightning properties (e.g., typically with high peak currents > -80 kA and large iCMCs > -300 C km) of negative sprites observed by the ISUAL are generally consistent with that documented in ground-based observations, but the ISUAL dataset does imply that sprites are sometimes produced by negative strokes with sub-critical iCMCs (less than -300 C km). Consequently, the future survey of global occurrence of sprites is desired to be based on complementary ground and space-borne observations. [ABSTRACT FROM AUTHOR]

The Imager of Sprites and Upper Atmospheric Lightning (ISUAL) has been operated for more than ten years. The onboard spectrophotometer channel-1 (SP1) was designed to detect the far-ultraviolet (FUV) emissions (N2 Lyman-Birge-Hopfield band) from space. It was found that most of the transient luminous events (TLEs), such as sprites, halos, elves, and gigantic jets, are usually accompanied by FUV emissions. The FUV emission could be utilized as an indicator for searching TLEs because the FUV emission of lightning is severely attenuated in the atmosphere during propagation, although the TLE FUV emissions are still detectable. Furthermore, the elves FUV emission photon flux can also be used to estimate the parent lightning peak current. Therefore, SP1 sensitivity degradation assessment, which affects the observed intensity of FUV emissions, is important. Although ISUAL has a lightemitting diode (LED) which is preset as a standard light source, the emission wavelength range of the LED does not cover the FUV band. We established a method in this study to determine the ISUAL Imager and SP1 sensitivity degradation. We found that the annual degradation rates of the ISUAL Imager and the SP1 are 8.4 and 9.7%, respectively. [ABSTRACT FROM AUTHOR]

Sprites are brief optical emissions occurring above thunderstorms. Features of sprites and their parent thunderstorms and lightning activities have been studied by many researchers. Here, we report a single sprite recorded over a mesoscale convective system during its life cycle in Northeast China. The results show that the sprite might have been a dancing one, with a 20 km horizontal displacement from its parent cloud-to-ground flash (CG) and a 38 ms time delay; all the sprite elements occurred during the continuing current process of the parent flash. The peak current of the parent CG was the largest during the almost one-hour time window containing the sprite, and the absolute values of all the negative flashes were smaller than 100 kA during the same time period and did not produce sprite. The sprite did not occur during the time period in which the maximum area of the thunderstorm reached. The occurrence of sprite corresponded well with the decay of the thunderstorm convection, and no significant relationship between the occurrence of sprite and the increase in the 30-35 dBZ and 35-40 dBZ interval was found. The large wind gradient in the 8-12 km region of the thunderstorm may have played an important role in the sprite production. [ABSTRACT FROM AUTHOR]

The positive downward propagating streamers of sprites are considered as factors of vertical coupling in middle atmosphere. Sprites are initiated in the lower ionosphere (at 75–85 km) and their streamers propagate in the mesosphere and upper stratosphere where the solar activity (SA) can have significant influence. The problem considered by us is whether sprites are sensitive to the solar activity. Different possible ways of such influence are considered. They concern: i) relations between solar activity and the occurrence of sprite-producing lightning discharges; ii) sensitivity of streamer inception to solar variability; iii) 11-year variations of conductivity in the night-time mesosphere and stratosphere during solar cycle due to modulation of the galactic cosmic ray flux by solar activity, which can lead to changes in sprite-driving electric fields, and therefore, in sprites. Accounting for the effects of sprites on minor constituents (in particular NO x ), a link between SA level and the che^mical balance in the mesosphere and stratosphere is considered, as well. With respect to this we study by modeling the response of the sprite-driving electric fields to SA variations with the account to a complex of parameters of sprite-producing lightning discharges and atmospheric conductivity. The lightning-driven electric fields needed for streamer propagation show minor dependence on conductivity changes caused by variations in cosmic ray flux during a solar cycle. The long-term changes in sprite's lower boundary by different parameters of lightning discharges and atmospheric conductivity parameters are estimated. During solar minimum, of the vertical dimension of sprites increases by up to 1.5 km than those during solar maximum. We estimate also the effect of the reduction of conductivity in thunderclouds with respect to the adjacent air. Reduction of cloud conductivity by a factor of 5–10 leads to larger vertical dimension of sprites due to descending of the sprite lower boundary by up to 5 km related to the case of unmodified cloud conductivity. The solar variability has significantly bigger effect on the sprite vertical dimension by larger charge moment change of the parental lightning discharge and by large reduction of the cloud conductivity. [ABSTRACT FROM AUTHOR]

The main goal of the JEM-EUSO experiment is the study of Ultra High Energy Cosmic Rays (UHECR, 10−10 e V), but the method which will be used (detection of the secondary light emissions induced by cosmic rays in the atmosphere) allows to study other luminous phenomena. The UHECRs will be detected through the measurement of the emission in the range between 290 and 430 m, where some part of Transient Luminous Events (TLEs) emission also appears. This work discusses the possibility of using the JEM-EUSO Telescope to get new scientific results on TLEs. The high time resolution of this instrument allows to observe the evolution of TLEs with great precision just at the moment of their origin. The paper consists of four parts: review of the present knowledge on the TLE, presentation of the results of the simulations of the TLE images in the JEM-EUSO telescope, results of the Russian experiment Tatiana-2 and discussion of the possible progress achievable in this field with JEM-EUSO as well as possible cooperation with other space projects devoted to the study of TLE - TARANIS and ASIM. In atmospheric physics, the study of TLEs became one of the main physical subjects of interest after their discovery in 1989. In the years 1992 - 1994 detection was performed from satellite, aircraft and space shuttle and recently from the International Space Station. These events have short duration (milliseconds) and small scales (km to tens of km) and appear at altitudes 50 - 100 km. Their nature is still not clear and each new experimental data can be useful for a better understanding of these mysterious phenomena. [ABSTRACT FROM AUTHOR]

We present multi-instrumented measurements and multi-technique analysis of polar cap patches observed early during the recovery phase of the major magnetic storm of 20 November 2003 to investigate the origin of the polar cap patches. During this event, the Qaanaaq imager observed elongated polar cap patches, some of which containing variable brightness; the Qaanaaq digisonde detected abrupt NmF2 fluctuations; the Sondrestrom incoherent scatter radar (ISR) measured patches placed close to but poleward of the auroral oval-polar cap boundary; and the DMSPF13 satellite intersected topside density enhancements, corroborating the presence of the patches seen by the imager, the digisonde, and the Sondrestrom ISR. A 2-D cross-correlation analysis was applied to series of two consecutive red-line images, indicating that the magnitude and direction of the patch velocities were in good agreement with the SuperDARN convection patterns. We applied a back-tracing analysis to the patch locations and found that most of the patches seen between 20:41 and 21:29UT were likely transiting the throat region near 19:41 UT. Inspection of the SuperDARN velocities at this time indicates spatial and temporal collocation of a gap region between patches and large (1.7 km s-1) lineof- sight velocities. The variable airglow brightness of the patches observed between 20:33 and 20:43 UT was investigated using the numerical Global Theoretical Ionospheric Model (GTIM) driven by the SuperDARN convection patterns and a variable upward/downward neutral wind. Our numerical results indicate that variations in the airglow intensity up to 265 R can be produced by a constant 70ms-1 downward vertical wind. [ABSTRACT FROM AUTHOR]

We present statistical analysis of 436 sprites observed in 7 winter campaigns from 2006/7–2012/13. Results show a clear peak in the frequency of sprite detections, with maximum values (< 40% of events) between 00:30 and 02:15 LST (22:30–00:15 UT; LST = UT + 2). The detection times of sprites are well-correlated with a relative increase in the fraction of + CG strokes, which exhibit maxima between 00:00 and 02:00 LST. The morphological distribution of 339 sprites, that we were able to clearly identify, is dominated by column sprites (49.3%), with angels (33.0%) and carrots (25.7%) being less frequent. This is similar to reports of winter sprites over the Sea of Japan and summer ones in Central Europe. Other shapes such as trees, wishbones, etc. appear quite rarely. Single element events constitute 16.5% of observations, with 83.5% containing 2 elements or more. Clusters of homogenous types are slightly more frequent than mixed ones (55%). Our observations suggest winter Mediterranean thunderstorms to have a vertical structure in between high tropical convective systems and the lower cloud-top cells in Japan. The climatology shows the Eastern Mediterranean to be a major sprite producer in Northern Hemisphere winter, and offers ground-based coverage for future space missions. [ABSTRACT FROM AUTHOR]

Atmospheric infrasound of frequencies 0.1–4 Hz observed in Central Europe during convective storms on 9–10 July 2011 from 21:00 to 02:57 UT was analysed. Azimuth of signal arrival followed positions of the convective storms passing over the region of measurements from south-west to north-east. Significant variations in azimuths of signal arrival (up to 105°) occurred periodically between 21:30 and 23:00 UT, at the time of maximum development of convective storms. Sprites (discharges in the mesosphere) seem to be potential sources of these infrasound signals. Stable infrasound arrivals were observed between 02:00 and 02:57 UT from direction where abating convective storms were located. [ABSTRACT FROM AUTHOR]

Based on MSIS90 atmospheric and 3D NeUoG ionospheric models, three types of ionospheric disturbances, i. e. ionospheric storm, traveling ionospheric disturbance (TID) and ionospheric trough were simulated, and their effects on bending angle residual ionospheric errors (RIEs) and temperature accuracy were analyzed. The results show that under high solar activity level, the bending angle RIE and its standard deviation can reach 1.5 μrad and 0.9 μrad, in the impact height range of 35~50 km; 4 μrad and 1.4 μrad, respectively, in the impact height range of 15~35 km. The ionopsheric storm and trough can enlarge the bending angle RIE standard deviations by more than 20 times, and TID can enlarge the bending angle RIE standard deviations by several times. Under the influence of ionospheric disturbances, temperature errors can reach 8 K and can pollute the GPS RO daily-mean and month-mean observations. Hence, it is desirable to develop ionospheric correction algorithms; the temperature outliers caused by ionospheric disturbances should be removed according to ionospheric monitoring results. [ABSTRACT FROM AUTHOR]

We study the effect of lightning on the lower ionosphere of Saturn. A self-consistent one-dimensional model of the electric field and electron density is used to estimate the changes of the local electron and photon emissions. The chemical fingerprint and ion densities are determined using a detailed self-consistent kinetic model. Charge moment change, depth of lightning flashes and their duration are estimated based on the known constraints of saturnian lightning activity. We test two electron density profiles and find that the conservative estimation of lightning charge moment change 10 4 to 10 5 C km could lead to faint halos and possibly sprites if the base of the ionosphere is located at 1000 km above the 1 bar level; if the base of the ionosphere is located at 600 km then only the extreme scenario of a 10 6 C km charge moment change could induce considerable ionization, halos and possibly sprites. We found that H 3 + ions are rapidly produced from the parent H 2 + ions through the fast reaction H 2 + + H 2 → H 3 + + H, so that H 3 + becomes the dominant ion in all the scenarios considered. The resulting light emissions, mostly in the blue and ultraviolet spectral regions, are below the detection threshold of Cassini. [ABSTRACT FROM AUTHOR]

The article discusses a study which describes the recordings of sprites using video cameras, which detect the radiants and characteristics of meteors. Topics include the first recorded sprite on July 23, 2013 by the NEMETODE, a meteor observation network in Great Britain, the estimation of an event's duration by inspecting the video fields, and the use of the UFO software from SonotaCo, a software company.

In the framework of C. Wilson's hypothesis substantiating a possibility of electric discharge development in the Earth's atmosphere at high altitudes above thunderclouds, numerical simulations were executed of the discharge exciting the sprite halo with realistic variations of thundercloud dipole moment transferred to the ground by positive lightning discharge. For various values of time and altitude, at which the avalanche-to-streamer transition occurs, optical radiation was calculated in the 1 P, 2 P, and 1 N bands of the nitrogen molecule and Meinel's band of the N ion. The calculated brightness and space-time evolution of the luminescence are consistent with the data of the field observations of the halo luminescence. [ABSTRACT FROM AUTHOR]

Abstract: Optical observations of 66 sprites, using a calibrated commercial CCD camera, were conducted in 2009–2010 and 2010–2011 winter seasons as part of the ILAN (Imaging of Lightning And Nocturnal flashes) campaign in the vicinity of Israel and the eastern Mediterranean. We looked for correlations between the properties of parent lightning (specifically, the charge moment change; CMC) to the properties of column sprites, such as the measured radiance, the length and the number of column elements in each sprite event. The brightness of sprites positively correlates with the CMC (0.7) and so does the length of sprite elements (0.83). These results are in agreement with previous studies, and support the QE model of sprite generation. [Copyright &y& Elsevier]

Sprites are optical emissions in the mesosphere mainly at altitudes 50-90 km. They are caused by the sudden re-distribution of charge due to lightning in the troposphere which can produce electric fields in the mesosphere in excess of the local breakdown field. The resulting optical displays can be spectacular and this has led to research into the physics and chemistry involved. Imaging at faster than 5,000 frames per second has revealed streamer discharges to be an important and very dynamic part of sprites, and this paper will review high-speed observations of sprite streamers. Streamers are initiated in the 65-85 km altitude range and observed to propagate both down and up at velocities normally in the 10-5 × 10 m/s range. Sprite streamer heads are small, typically less than a few hundreds of meters, but very bright and appear in images much like stars with signals up to that expected of a magnitude −6 star. Many details of streamer formation have been modeled and successfully compared with observations. Streamers frequently split into multiple sub-streamers. The splitting is very fast. To resolve details will require framing rates higher than the maximum 32,000 fps used so far. Sprite streamers are similar to streamers observed in the laboratory and, although many features appear to obey simple scaling laws, recent work indicates that there are limits to the scaling. [ABSTRACT FROM AUTHOR]

This paper presents a literature survey on the recent developments related to modeling studies of transient luminous events termed sprites and sprite halos that are produced at mesospheric and lower ionospheric altitudes in the Earth's atmosphere by lightning. The primary emphasis is placed on publications that appeared in the refereed literature starting from year 2010 and up to the present date. The survey focuses on the interpretation of morphological features observed in sprites. We introduce parameters typically used for quantitative description of electron avalanches and discuss the importance of space charge effects on different spatial scales, including sprite halos (exhibiting 10s of km transverse extents) and sprite streamers (requiring submeter resolution for accurate description). A special emphasis is placed on the interpretation of initiation and development of sprite streamers captured in high-speed video observations and a critical review of the most recent modeling efforts related to these observations. We also discuss fundamental reasons for polarity asymmetry in existing sprite observations indicating that vast majority of sprites with well-developed streamer structure are produced by positive cloud-to-ground lightning discharges. [ABSTRACT FROM AUTHOR]

Three summer thunderstorms in the eastern region of China were analyzed in detail using multiple data, including Doppler radar, lightning location network, TRMM (Tropical Rainfall Measuring Mission), MTSAT (Multi-Function Transport Satellite) images, NCEP (National Centers for Environmental Prediction) Reanalysis, and radiosonde. Two of the three storms were sprite-producing and the other was non-spriteproducing. The two sprite-producing storms occurred on 1-2 August and 27-28 July 2007, producing 16 and one sprite, respectively. The non-sprite-producing storm occurred on 29-30 July 2007. The major objective of the study was to try to find possible differences between sprite-producing and non-sprite producing storms using the multiple datasets. The results showed that the convection in the 1-2 August storm was the strongest compared with the other storms, and it produced the largest number of sprites. Precipitation ice, cloud ice and cloud water content in the convective regions in the 1-2 August storm were larger than in the other two storms, but the opposite was true in the weak convective regions. The storm microphysical properties along lines through parent CG (cloud-to-ground lightning) locations showed no special characteristics related to sprites. The flash rate evolution in the 1-2 August storm provided additional confirmation that major sprite activity coincides with a rapid decrease in the negative CG flash rate. However, the evolution curve of the CG flash rate was erratic in the sprite-producing storm on 27-28 July, which was significantly different from that in the 1-2 August storm. The average positive CG peak current in sprite-producing storms was larger than that in the non-sprite-producing one. [ABSTRACT FROM AUTHOR]

Abstract: Twenty-nine sprites were observed during four years from 2007 to 2010 with one most sprite-productive storm on 1–2 August 2007 which produced 16 sprites. In this paper, the most sprite-productive storm is analyzed by using data from lightning detection network, Doppler radar, MTSAT (Multi-Function Transport Satellite) satellite, TRMM (Tropical Rainfall Measuring Mission), NCEP. The results show that most sprites appeared in groups and in shape of carrot. Most sprites occurred frequently when the cloud top brightness temperature is getting warm and radar reflectivity is becoming weak with characteristics of sharp decrease of negative CGs and slight increase of positive CGs. The parent cloud-to-ground lightning flashes (CGs) were positive and located in region with cloud top brightness temperature of −40 to −60°C and radar reflectivity of 15–35dBZ. The sprite-producing storm was fortunately scanned by TRMM during sprite time period. One orbit data could be used for PR (Precipitation Radar, 2A25) and two orbit data for TMI (TRMM Microwave Imager, 2A12 and 1B11). Results based on TRMM indicated that storm reflectivity with 30dBZ was at about 12km in the convective region and 4km in stratiform region. The precipitation ice mostly located in 6–8km with the largest value of 2.1g/m3, but most cloud ice located between 10 and 14km with no cloud ice below 6km and very few at 6.0–8.0km. The cloud water content located mostly between 4 and 6km. Characteristics of vertical cross sections of radar reflectivity, precipitation ice and cloud ice agree well. Vertical cross sections along convective and stratiform regions show that contents of precipitation ice and cloud ice in convective region were larger than that in stratiform region. But cloud water in stratiform region was larger than that in convective region. The storm evolution could be seen clearly from characteristics of precipitation ice, cloud ice, cloud water and polarization corrected temperature at two different times. The CG distribution agrees well with low values of polarization corrected temperature region, indicating that lightning flashes have close relationship with ice particles. Although this paper is a case study of sprite-producing thunderstorm based on TRMM data, the results provided detailed information of microphysical structure of this sprite-producing storm. [Copyright &y& Elsevier]

This paper gives a resume of the papers written in English which (a) describe some of the recording instruments in use at the Nagycenk Observatory (NCK) since the International Geophysical Year (IGY 1957-1958) and up to the present time, (b) summarise the most important and different types of observations associated with thunderstorms which have been made there, and (c) discuss their various geophysical interpretations. The paper describes the main results which have been obtained in four areas of thunderstorm associated atmospheric and geospace science within the context of Earth system science. These relate to the following parameters of atmospheric electricity: the vertical electric potential gradient just above the Earth's surface and the air-Earth current as well as the point discharge current, Schumann resonance (SR) signals of the Earth-ionosphere cavity at 8, 14 and 20 Hz, transient luminous events (TLEs), and some aspects of the behaviour of the ionosphere. Deductions from these data sets are concerned with the global lightning activity and the conductivity of the air, with diurnal, seasonal, annual and long-term variations of the SR amplitudes and resonant frequencies in terms of migrating thunderstorm centres, with transient SR excitations and with sprites and other TLEs, and with ionospheric disturbances. The paper closes with some thoughts on future research directions based on the observations at NCK and Sopron and the results achieved since the IGY. [ABSTRACT FROM AUTHOR]

In measurements of the electric field associated with the current of a sprite 450 km from ground-based field sensors, it was observed that the sign of the electric field was positive when positive charge was lowered from the ionosphere. A recent model for the electric field associated with the sprite current also predicts positive field changes at 450 km from the sprite. A well-known analysis of a vertical dipole in a thundercloud shows that the electric field on the ground reverses its sign at an easily computed distance from the dipole. A similar simplified electrostatic analysis of a sprite predicts a field reversal distance around 130 km. A more accurate electrodynamic analysis based on Maxwell's equations indicates that the field reversal distance should be between 70 and 80 km. [ABSTRACT FROM AUTHOR]

Sprites are Transient Luminous Events (TLEs) consisting of hundreds of streamer discharges. After the passage of a streamer head, some persistent structures develop in the ionized channel left behind. Observations show lateral streamers emerging from these structures known as beads and glows. Long laboratory discharges also show analogue burst of lateral streamers from glows. In our simulations we have observed the emergence of glow-like structures or space stem precursors. These regions inside the streamer wake and ahead of a negative leader have a low conductivity and an electric field higher than the surrounding channel.Glows and beads are the origin of lateral streamers. These lateral streamers influence the dynamics of the corona by interacting with other streamers, reconnecting to the electrode or the leader and possibly influencing the conductivity of others channels noticeably. Therefore, it is crucial to elucidate the lifespan of these space stems as well as the conditions under which the lateral streamers launch from these regions. [ABSTRACT FROM AUTHOR]

In dancing sprite events, sprite entities and groups appear in rapid succession together with a corresponding series of parent lightning strokes. Dancing sprite events, including a case with possible sprite rebrightening, were recorded on video simultaneously from two observation sites above a mesoscale convective system in Central Europe on the night of 6 August 2013. Joint analysis of triangulated locations of sprite elements, position, type, and peak current of lightning strokes from the LINET lightning detection network database and current moment waveforms deduced at the Hylaty station, Poland, showed that subsequent sprite‐parent lightning strokes occurred no further than 21 km from the closest preceding sprite entity in the cases analyzed in this study. Additionally, it was found that longer sprite delay times tend to correspond to larger sprite location offsets from the parent +CG stroke. These observations, the occurrence of +CG lightning stroke and sprite sequences, as well as sprite‐sprite delay times and displacements can be explained if +CG strokes are part of one extended lightning flash. A corresponding production mechanism based on previous findings on the formation of sprite‐producing and general +CG lightning discharges is suggested. Plain Language Summary: In dancing sprite events, sprites appear in rapid succession together with a corresponding series of parent lightning strokes. Dancing sprite events were recorded on video simultaneously from two observation sites above an extended thunderstorm system in Central Europe on the night of 6 August 2013. Comparison of triangulated sprite locations and the locations of corresponding lightning activity revealed that subsequent sprite‐parent lightning strokes occurred below or relatively near the location of the closest preceding sprite entity in the examined cases. In this paper, a mechanism is suggested for the development of lightning flashes that produce dancing sprites. The proposed mechanism accounts for prompt and delayed sprites relative to their parent lightning stroke, highlights the role of the variation of lightning current in sprite production, and can explain the observed closeness of the next +CG lightning stroke to the area of previous sprites. Key Points: The observations support that dancing sprite events tend to occur above stratiform cloud areasIf a sprite is up to 45 km away from its parent +CG stroke, the offset of the next sprite in the same sequence was found to be largerIt is suggested that +CG parent strokes in dancing sprite events are often part of one extensive lightning flash [ABSTRACT FROM AUTHOR]

The article offers information on the initial observations of flashes of lightning discharge observed above thunderstorms. It mentions that the transient luminous events (TLE) are classified on the basis of their geometrical shape and luminosity into Sprites, Halos and Blue Starters. It also focuses on the first sprite observed in the Indian subcontinent on April 11, 2012, whose optical measurements were conducted at Allahabad, India using the charge-coupled device camera system.

Sprites and halos are two types of the so-called transient luminous events occurring in the upper layers (40–90 km) of the earth atmosphere. Their spectacular appearance is due to the optical emissions from mesospheric plasmas caused by the electric breakdown of the high-altitude rarified air. While halos look like flattened diffuse flashes of light appearing between 80 and 85 km, sprites exhibit a sharp transition between the upper diffuse and lower plasma streamer regions, as observed in one of the images shown here. [ABSTRACT FROM PUBLISHER]

Streamers are rapidly extending ionized finger-like structures that dominate the initial breakdown of large gas volumes in the presence of a sufficiently strong electric field. Their macroscopic parameters are described by simple scaling relations, where the densities of electrons and of excited molecules in the active streamer front scale as the square of the density of the neutral gas. In this work we estimate the absolute density of nitrogen molecules, excited to the C3Πu state that emit photons in the 2P–N2 band, by radiometrically calibrated short exposure intensified imaging. We test several pressures (100, 200 and 400 mbar) in artificial air at room temperature. Our results provide a first confirmation for the scaling of the density of excited species with the gas density. The method proposed here is particularly suitable to characterize the excitation densities in sprite streamers in the atmosphere. [ABSTRACT FROM AUTHOR]

Propagation and splitting of sprite streamers has been observed at high temporal and spatial resolution using two intensified high-speed CMOS cameras recording at 10 000 and 16 000 frames per second. Concurrent video recordings from a remote site provided data for triangulation allowing us to determine accurate altitude scales for the sprites. Diameters and speeds of the sprite streamers were measured from the high-speed images, and the diameters were scaled to the reduced diameters based on the triangulated locations. The sprite streamers with larger reduced diameter move faster than those with smaller diameter; the relation between the reduced diameter and speed is roughly linear. The reduced diameters at ≈65–70 km altitude are larger than streamer diameters measured at ground pressure in laboratory discharges indicating a deviation from the similarity law possibly due to the effects of the photoionization and an expansion of the streamer head along its propagation over a long distance. The reduced diameter and speed of the sprite streamers agree well with the diameter–velocity relation proposed by Naidis (2009 Phys. Rev. E 79 057401), and the peak electric field of the sprite streamers is estimated to be approximately 3–5 times the breakdown threshold field. [ABSTRACT FROM AUTHOR]