Observations Of Transient Luminous Events Research Articles

Contrast between continental and oceanic thunderstorms in producing red sprites and halos

The observations of transient luminous events from space-borne platform extend our exploration on the mysteries of sprite phenomenology from continental thunderstorms to oceanic thunderstorms. By combining with ground-based measurements of causative strokes for hundreds of red sprites observed by the Imager of Sprites and Upper Atmospheric Lightnings (ISUAL) during 2004–2016, there is a consensus that negative cloud-to-ground (CG) strokes spawned by oceanic thunderstorms are more readily to produce sprites. The existing ground-based observations in both Caribbean Sea and near the coast of South China, mainly due to the contributions from numerous amateurs, are generally consistent with the implications of ISUAL observations. However, the physical mechanisms that might cause the enhancement of negative CG strength in the ocean remain not completely understood. There have been analyses on several cases of oceanic thunderstorms abundant in producing negative sprites. It seems that the production of negative sprites heavily depends on the size of parent thunderstorms, and they are often generated by thunderstorm conditions that are also favorable for gigantic jets.

Design and construction of hardware and software for autonomous observations of Transient Luminous Events

Transient luminous events (TLE) are phenomena which are currently on the rise in terms of sightings. However, there is no widespread uniform method of their observation and subsequent image processing. Therefore, our project focuses on the design and construction of hardware that can record TLE. It consists of a low gain, colour, CMOS camera with a bright, wide lens connected to a small, power-efficient single board computer. The project also includes writing software to control the hardware. The software decides whether to capture or not and at what orientation there is the biggest chance to capture a TLE. The software can process and classify the created photos based on deep neural networks. As a final product, we have developed the whole apparatus from a hardware and software point of view and installed it at the Astronomical Observatory at Kolonica Saddle in Slovakia, Central Europe. The plan for the future is to make similar apparatuses to spread the observation network.

Survey of electron density changes in the daytime ionosphere over the Arecibo Observatory due to lightning and solar flares

Optical observations of transient luminous events and remote-sensing of the lower ionosphere with low-frequency radio waves have demonstrated that thunderstorms and lightning can have substantial impacts in the nighttime ionospheric D region. However, it remains a challenge to quantify such effects in the daytime lower ionosphere. The wealth of electron density data acquired over the years by the Arecibo Observatory incoherent scatter radar (ISR) with high vertical spatial resolution (300-m in the present study), combined with its tropical location in a region of high lightning activity, indicate a potentially transformative pathway to address this issue. Through a systematic survey, we show that daytime sudden electron density changes registered by Arecibo’s ISR during thunderstorm times are on average different than the ones happening during fair weather conditions (driven by other external factors). These changes typically correspond to electron density depletions in the D and E region. The survey also shows that these disturbances are different than the ones associated with solar flares, which tend to have longer duration and most often correspond to an increase in the local electron density content.

Possible Transient Luminous Events Observed in Jupiter's Upper Atmosphere

AbstractEleven transient bright flashes were detected in Jupiter's atmosphere using the ultraviolet spectrograph instrument on the Juno spacecraft. These bright flashes are only observed in a single spin of the spacecraft and their brightness decays exponentially with time, with a duration of ∼1.4 ms. The spectra are dominated by H2 Lyman band emission and based on the level of atmospheric absorption, we estimate a source altitude of 260 km above the 1‐bar level. Based on these characteristics, we suggest that these are observations of transient luminous events (TLEs) in Jupiter's upper atmosphere. In particular, we suggest that these are elves, sprites or sprite halos, three types of TLEs that occur in the Earth's upper atmosphere in response to tropospheric lightning strikes. This is supported by visible light imaging, which shows cloud features typical of lightning source regions at the locations of several of the bright flashes. TLEs have previously only been observed on Earth, although theoretical and experimental work has predicted that they should also be present on Jupiter.

First 10 Months of TGF Observations by ASIM

AbstractThe Atmosphere‐Space Interactions Monitor (ASIM) was launched to the International Space Station on 2 April 2018. The ASIM payload consists of two main instruments, the Modular X‐ray and Gamma‐ray Sensor (MXGS) for imaging and spectral analysis of Terrestrial Gamma‐ray Flashes (TGFs) and the Modular Multi‐spectral Imaging Array for detection, imaging, and spectral analysis of Transient Luminous Events and lightning. ASIM is the first space mission designed for simultaneous observations of Transient Luminous Events, TGFs, and optical lightning. During the first 10 months of operation (2 June 2018 to 1 April 2019) the MXGS has observed 217 TGFs. In this paper we report several unprecedented measurements and new scientific results obtained by ASIM during this period: (1) simultaneous TGF observations by Fermi Gamma‐ray Burst Monitor and ASIM MXGS revealing the very good detection capability of ASIM MXGS and showing substructures in the TGF, (2) TGFs and Elves produced during the same lightning flash and even simultaneously have been observed, (3) first imaging of TGFs giving a unique source location, (4) strong statistical support for TGFs being produced during the upward propagation of a leader just before a large current pulse heats up the channel and emits a strong optical pulse, and (5) the t50 duration of TGFs observed from space is shorter than previously reported.

Climatology of Transient Luminous Events and Lightning Observed Above Europe and the Mediterranean Sea

In 1999, the first sprites were observed above European thunderstorms using sensitive cameras. Since then, Eurosprite campaigns have been conducted to observe sprites and other transient luminous events (TLEs), expanding into a network covering large parts of Europe and coastal areas. In 2009 through 2013, the number of optical observations of TLEs reached a peak of 2000 per year. Because of this unprecedented number of European observations, it was possible to construct a climatology of 8394 TLEs observed above 1018 thunderstorm systems and study for the first time their distribution and seasonal cycle above Europe and parts of the Mediterranean Sea. The number of TLEs per thunderstorm was found to follow a power law, with less than 10 TLEs for 801 thunderstorms and up to 195 TLEs above the most prolific one. The majority of TLEs were classified as sprites, 641 elves, 280 halos, 70 upward lightning, 2 blue jets and 1 gigantic jet. The climatology shows intense TLE activity during summer over continental areas and in late autumn over coastal areas and sea. The two seasons peak, respectively, in August and November, separated by March and April with almost no TLEs, and a relative minimum around September. The observed TLE activity, i.e. mostly sprites, is shown to be largely consistent with lightning activity, with a 1/1000 of observed TLE-to-lightning ratio in regions with most observations. The overall behaviour is consistent among individual years, making the observed seasonal cycle a robust general feature of TLE activity above Europe.

Universat-SOCRAT multi-satellite project to study TLEs and TGFs

We present concept of a new multi-satellite Universat-SOCRAT project aimed to study transient phenomena in the upper atmosphere such as transient luminous events (TLEs) and terrestrial gamma-ray flashes (TGFs). It is a new space project of Lomonosov Moscow State University based on the use of a few satellites in the near-Earth orbit for real-time monitoring of radiation environment, natural (asteroids, meteoroids) and artificial (space debris) potentially dangerous objects, electromagnetic transients including cosmic gamma-ray bursts, terrestrial gamma-ray flashes, and optical and ultraviolet bursts in the Earth’s atmosphere.Study of TLEs and TGFs remains an important and demanding task despite of a multitude of recently acquired data for these phenomena. This might be explained by the absence of comprehensive theoretical understanding of physical nature of high-energy processes in the Earth’s atmosphere. Multi-wavelength synchronous observations with moderate accuracy of localization of TGF and TLE events are necessary to gain an insight of physics governing these high-energy processes in the Earth’s atmosphere. In the article, we present results of TLE observations in space experiments of Moscow State University and discuss advanced instruments for optical observations of TLEs, as well as gamma-ray burst monitor and tracking gamma spectrometer for TGFs observations.

Experimental Validation of an Onboard Transient Luminous Events Observation System for VisionCube via Ground Simulation Environment

The VisionCube is a 2-unit CubeSat developed in house, of which the primary mission is detecting the occurrence of transient luminous events (TLEs) in the upper atmosphere and obtaining corresponding images from a low Earth orbit. An onboard TLE observation system of the VisionCube CubeSat is designed and developed by incorporating a photon-sensitive multi-anode photon-multiplier tube (MaPMT) and an image sensor. Also, a distinctive TLE observation software which enables detection of the TLEs and capture of images in a timely manner is devised. By taking into account the limited resources of a small CubeSat in size and power, the onboard observation system is developed employing a system-on-chip device by which both hardware and software can be integrated seamlessly. The purpose of this study is to investigate the functionality of the hardware and the validity of the software algorithm to show that the onboard system will function properly with no human intervention during the operations in space. To this end, a ground simulation facility is constructed to emulate TLEs occurring in space using a set of ultraviolet light-emitting diodes (UV LEDs) inside a darkbox. Based on the analysis of the spectral and temporal properties of the TLEs, the randomly generated UV LED pulses are chosen for verification scenarios for the TLE observation system. The validation results show that the hardware and the software algorithm of the onboard observation systems can effectively detect the TLEs and obtain the images during the in-orbit operation.

Determination of sprite streamers altitude based on N2 spectroscopic analysis

AbstractFuture space missions (e.g., ASIM and TARANIS) are soon to be launched to observe transient luminous events (TLEs) from a nadir‐viewing geometry. The mission GLIMS already performed observations of TLEs from a nadir‐viewing geometry on board the International Space Station. Although this observation geometry is of first interest to study TLEs, it makes the determination of some quantities, such as streamer altitudes, very difficult. In this study, we propose a method to estimate the altitude of downward propagating sprite streamers using a spectrophotometric approach. Using a plasma fluid model, we simulate sprite streamers at different altitudes and quantify their optical emissions in the Lyman‐Birge‐Hopfield (LBH) (∼100–260 nm), the first positive (1PN2) (∼650–1070 nm), and the second positive (2PN2) (∼330–450 nm) bands systems of molecular nitrogen and the first negative ( ) (∼390–430 nm) bands systems of . The estimation of associated ratios allows to trace back the electric field in the streamer head as well as the altitude at which the streamer is propagating owing to different dependencies of quenching processes on the air density. The method takes into account the nonsteady state of the populations of some excited species and the exponential expansion of the streamer. The reported results could potentially be used for all TLEs but is of special interest in the case of column sprites or at the early stage of carrot sprites.

High resolution spectroscopy of an Orionid meteor from 700 to 800 nm

The emission spectrum of a meteor was recorded by the GRASSP instrument during the observation of transient luminous events (TLEs) on 2014 October 16th. The spectroscopic signal was recorded in the wavelength range from 700 to 800nm, where the emission from atmospheric oxygen and nitrogen dominated. The good spectral resolution of the spectrum (0.24nm with 0.07nm/pixel spectral dispersion) has allowed us to determine the physical conditions in the meteor plasma, to identify several emissions from atmospheric (N I, N II, O I) and meteoroid species (Ti I, Cr I, Fe I, Fe II, Zr I, Pd I, W I) and to estimate the upper limit of the temperature of the gaseous environment surrounding the meteoroid. Images recorded for this meteor from two different sites allowed calculating its atmospheric trajectory and the orbital parameters of the progenitor meteoroid. These data revealed that the particle belonged to the Orionid meteoroid stream.

Ten-year transient luminous events and Earth observations of FORMOSAT-2

The purpose of this paper is to summarize the enormous contributions of FS2 (FORMOSAT-2 or Formosa satellite #2) in both Earth and transient luminous events (TLEs) observations in 10 years. As a small satellite operated for 10 years (20 May 2004 to 20 May 2014) in orbit, FS2 keeps its two unique characteristics: (1) to orbit 14 revolutions around the Earth per day with daily revisit capability, and (2) to provide the capabilities of Earth observation in sunlight time and TLEs observation in eclipsed time every day. It carries two payloads: the remote sensing instrument (RSI) for Earth imaging in satellite׳s day time and the imager of sprites and upper atmospheric lightning instrument (ISUAL) for scientific observations in satellite׳s night time, respectively. Daily revisit capability provides changes of events on Earth in either short time (several days) or long term (several years). Examples include: Indian Ocean earthquake and tsunami (December 2004), disintegration of Wilkins Ice Shelf in Antarctica region (2006–2014, long term), Sichuan earthquake (May 2008), Tohoku earthquake and tsunami (March 2011), polar regions (2006–2014, long term), etc. In the TLEs observation, ISUAL had recorded more than 35,000 events in 10 years with 73.93% elves, 6.54% red sprites, 5.81% halos, 13.42% blue jets and 0.30% gigantic jets. Major contributions of FS2 in this specific scientific area are presented. In particular, current and future research topics on TLEs are discussed. Also, major contributions of FS2׳s RSI to the United Nations Institute for Training and Research (UNITAR) Operational Satellite Applications Programme (UNOSAT) and Group of Earth Observation System of Systems (GEOSS) are summarized. This paper also addresses briefly the health status of FS2 after working 10 years in orbit.

First observations of transient luminous events in Indian sub-continent

First observations of transient luminous events in Indian sub-continent

Simulation of the capabilities of an orbiter for monitoring the entry of interplanetary matter into the terrestrial atmosphere

In comparison with existing ground-based camera networks for meteors monitoring, a space-based optical system would escape dependency on weather and atmospheric conditions and would offer a wide spatial coverage and an unrestricted and extinction-free spectral domain. The potential rates of meteor detections by such systems are evaluated in this paper as a function of observations parameters (optical system capabilities, orbital parameters) and considering a reasonable range of meteoroids properties (e.g., mass, velocity, composition) determining their luminosity. A numerical tool called SWARMS (Simulator for Wide Area Recording of Meteors from Space) has been developed. SWARMS is also intended to be used in an operational phase to facilitate the comparison of observations with up-do-date constraints on the flux and characteristics of the interplanetary matter entering our planet׳s atmosphere. The laws governing the conversion of a fraction of the meteor kinetic energy into radiation during atmospheric entry have been revisited and evaluated based on an analysis of previously published meteor trajectories. Rates of detection were simulated for two different systems: the SPOSH (Smart Panoramic Optical Sensor Head) camera optimized for the observation of transient luminous events, and the JEM-EUSO (Japanese Experiment Module-Extreme Universe Space Observatory) experiment on the ISS (International Space Station). We conclude that up to 6 events per hour in the case of SPOSH, and up to 0.67 events in the case of JEM-EUSO may be detected. The optimal orbit for achieving such rates of detections depends on the mass index of the meteoroid populations. The determination of this parameter appears therefore critical before an optimal orbiting system might be designed for meteors monitoring.

Globalization extension of transient luminous events from FORMOSAT-2 observation

Since its launch on 20 May 2004, FORMOSAT-2 (FS2) is still the unique satellite to observe the transient luminous events (TLEs) from orbit. In nearly 9 years from 4 July 2004 to 31 May 2013, the number and distribution of TLEs observed are summarized. The instrument used for the observation of TLEs is called imager of sprites and upper atmospheric lightning (ISUAL). This is the first time the observation results are presented in the International Astronautical Congress (IAC). Due to the orbital characteristics of FORMOSAT-2, unobserved gaps exist between each two orbits. Also, the ISUAL has its detection threshold. In this paper, besides the presentation of above results, globalization extension of TLEs is performed based on FORMOSAT-2׳s observation. Factors considered include number of orbits ISUAL in operations, daytime and night-time, season, non-observed areas, observability of TLEs, limb view hiding, and other factors. An estimated global occurrence rate is 24TLEs/min, but this number is still much less than the possible potential rate of 195. To enhance the results, more instruments and longer observation time are required.

Energetic Charged Particles Above Thunderclouds

The French government has committed to launch the satellite TARANIS to study transient coupling processes between the Earth’s atmosphere and near-Earth space. The prime objective of TARANIS is to detect energetic charged particles and hard radiation emanating from thunderclouds. The British Nobel prize winner C.T.R. Wilson predicted lightning discharges from the top of thunderclouds into space almost a century ago. However, new experiments have only recently confirmed energetic discharge processes which transfer energy from the top of thunderclouds into the upper atmosphere and near-Earth space; they are now denoted as transient luminous events, terrestrial gamma-ray flashes and relativistic electron beams. This meeting report builds on the current state of scientific knowledge on the physics of plasmas in the laboratory and naturally occurring plasmas in the Earth’s atmosphere to propose areas of future research. The report specifically reflects presentations delivered by the members of a novel Franco-British collaboration during a meeting at the French Embassy in London held in November 2011. The scientific subjects of the report tackle ionization processes leading to electrical discharge processes, observations of transient luminous events, electromagnetic emissions, energetic charged particles and their impact on the Earth’s atmosphere. The importance of future research in this area for science and society, and towards spacecraft protection, is emphasized.

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.

The Smart Panoramic Optical Sensor Head (SPOSH)—A camera for observations of transient luminous events on planetary night sides

We have developed a camera dedicated to imaging faint transient noctilucent phenomena, such as aurorae, electric discharges, meteors or impact flashes, on dark planetary hemispheres. The Smart Panoramic Optical Sensor Head (SPOSH) is equipped with a back-illuminated 1024×1024 CCD chip E2V 47–20 with up to 90% quantum efficiency and has a custom-made optical system of high light-gathering power with a wide field of view of 120°×120°. Images can be obtained over extended periods at high rate to make monitoring for transient events possible. To reduce the data transmission rate, only those images (or relevant portions thereof) that contain events are returned to the user. The camera has a sophisticated processing unit prepared to interface with a spacecraft system, for image processing and event detection at rates of up to 3 images per second at full resolution. While software optimized for detection of any noctilucent phenomenon can be implemented, the software is currently optimized for the detection of meteors. Over the past years, we have routinely carried out outdoor tests with 4 camera breadboard units that demonstrate that the camera has excellent radiometric performance and geometric resolution at low light levels over its large field of view. The camera has been demonstrated to capture meteors of magnitudes as faint as +6 m moving at angular speeds of 5°/s. The camera opens up new science opportunities for planetary missions.

Free‐running ground‐based photometric array imaging of transient luminous events

We present observations of transient luminous events (TLEs) recorded during a summer TLE observation campaign in 2008 at Langmuir Laboratory near Socorro, New Mexico. The campaign featured observations made by a free‐running, ground‐based multianode photometric array called the Photometric Imager of Precipitated Electron Radiation (PIPER). As a photometric array, PIPER has high (40 μs) temporal resolution and enough spatial resolution (16 anodes per photometer) to make it particularly useful in the study of fast TLEs like elves and halos. As a free‐running instrument, there are no missed detections and no unwanted sampling bias introduced by triggering. As a ground‐based instrument, it can follow individual storms over the course of their lifetime rather than randomly sampling over large numbers of storms as required by space‐based instruments. During the campaign, 143 sprites, 803 elves, and 166 halos were observed over six storms, resulting in averaged elve‐to‐sprite and halo‐to‐sprite occurrence ratios of 5.6:1 and 1.2:1, respectively. There was considerable variability in the elve‐to‐sprite occurrence ratio from storm to storm, ranging from a low of 3.7:1 to a high of 13.4:1. Overall, 78.2% of the elves and 55.4% of the halos were associated with negative cloud‐to‐ground lightning strikes (−CGs); no sprites associated with −CGs were observed. Additionally, 40 events in which pairs of elves occur in rapid succession, events we refer to as elve doublets, were observed in several storms. The duration between elves in the elve doublet events was typically 120 μs. The causative mechanism for these events is still under deliberation.

Space observations of Transient Luminous Events and associated emissions in the upper atmosphere above thunderstorm areas

Sprites, jets and elves called Transient Luminous Events (TLE), observed in the middle and upper atmosphere above thunderstorms, are the manifestation of intense energy exchanges between the troposphere, stratosphere and mesosphere. Different types of luminous emissions have been identified by ground-based observations, showing the complexity of these phenomena. Space missions showed that transient emissions in the Earth atmosphere are very broad including Radio Frequency (RF), IR to FUV radiations and X-gamma ray emissions called Terrestrial Gamma Flashes (TGF) with energies reaching 30 Mev. However, there are no global observations of these events together. This paper reviews space observations performed up to now and emphasizes the challenges of the future space missions in global measurements of all possible emissions together for the understanding of the physical mechanisms at the origin of these phenomena and their effects on the Earth environment.

Optical observations of transient luminous events associated with winter thunderstorms near the coast of Israel

We report the results of two observation campaigns conducted during the Northern Hemisphere winters of 2005–6 and 2006–7 aiming to detect transient luminous events (TLEs) above winter thunderstorms in the vicinity of Israel and the eastern coastline of the Mediterranean Sea. In 10 out of 31 different observation nights we detected 66 events: 56 sprites and 10 Elves. The detection ranges varied from 250 to 450 km. Sprites were found to be produced by active cells with a vertical dimension of 5–9 km and cloud top temperature ~ − 40 °C, embedded in a much larger matrix of stratiform precipitating cloudiness. This configuration closely resembles the conditions for winter sprites in the Hokuriku region of Japan. Synchronized with the optical observations, ELF data were recorded at two observation stations in Israel and Hungary in order to qualify and quantify parameters of the parent lightning discharge associated with the TLEs. These stations are located 500 km and 2100 km respectively from the Eastern Mediterranean Sea, where most TLEs occur. Among the optically observed TLE events, we found that all the ELF signals were produced solely by positive cloud-to-ground flashes (+ CGs), most of which were recorded in Israel (88%) and Hungary (77%). Calculation of the Charge Moment Change showed average values of 1400 ± 600 C km, with some extreme events exceeding 3500 C km. The average time delay between the ELF transient of the parent + CG and the observed sprites was 55 ms, with shorter delays for column sprites (42 ± 34 ms) compared to carrot sprites (68 ± 34). Furthermore, based on the ELF data, there were no early identifiable precursors to TLE occurrence in the regional lightning activity. From the spatial formation of the observed columniform sprites, we propose that columniform sprites are sometimes arranged in a 3-dimensional circular pattern, thus mapping the instantaneous electric field in the mesosphere.