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.

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

A study is conducted of the principal chemical effects induced by the passage of a single sprite streamer through the mesosphere at an altitude of 70 km. Recent high-speed imaging of sprite streamers has revealed them to comprise bright (1-100 GR), compact (decameter-scale) heads moving at ∼10 7 m s -1 . On the basis of these observations, a quantitative model of the chemical dynamics of the streamer head and trailing region is constructed using a nonlinear coupled kinetic scheme of 80+ species and 800+ reactions. In this initial study, chemical processes related to currents in the trailing column and to vibrational kinetics of N 2 and O 2 are not included. The descending streamer head impulsively (T ∼ 10 μs) ionizes the gas (fractional ionization density ∼10 -9 ), leaving in its trail a large population of ions, and dissociated and excited neutral byproducts. Electrons created by ionization within the head persist within the trailing column for about 1 s, with losses occurring approximately equally by dissociative attachment with ambient O 3 , and by dissociative recombination with the positive ion cluster N 2 O + 2 . The ion cluster is produced within the trailing channel by a three-step process involving ionization of N 2 , N + 2 charge exchange with O 2 , and finally three-body creation of N 2 O + 2 . On the basis of simulation results, it is concluded that the observed reignition of sprites most likely originates in remnant patches of cold electrons in the decaying streamer channels of a previous sprite. Relatively large populations (fractional densities ∼10 -9 -10 -8 ) of the metastable species O( 1 D), O( 1 S), N( 2 D), O 2 (a 1 Δ g ), O 2 (b 1 Σ + g ), N 2 (A 3 Σ + u ), and N 2 (a' 1 Σ - u ) are created in the streamer head. The impulsive creation of these species initiates numerous coupled reaction chains, with most of the consequent effects being of a transient nature persisting for less than 1 s. These include weak (∼1 kR), but possibly detectable, OI 557.7 nm and O 2 (b 1 Σ + g → X 3 Σ - g ) Atmospheric airglow emissions. Neutral active species created in the greatest abundance (fractional densities > 10 -8 ) are N 2 (X 1 Σ + g , ν), O( 3 P), N( 4 S), and O 2 (a 1 Δ g ), which, because of the absence of readily available chemical dissipation channels, persist for longer than 100s of seconds. Other long-lived (>1000 s) effects are very weak (∼1-10 R) OH(X 2 Π, ν = 6...9 - Δν) Meinel emissions produced by O( 3 P)-enhanced OH catalysis and O 2 (a 1 Δ g → X 3 Σ - g ) Infrared Atmospheric emissions. Short-lived (∼100 s) populations of hydrated positive ions and negative ion clusters are also created in the streamer trail. Electron impact dissociated N( 2 D) interacts with O 2 to create a long-lived (>1000 s) increase (fractional enhancement ∼75%) of the ambient NO density within the streamer channel, for a net production of ∼5 x 10 19 NO molecules for the streamer as a whole. It is suggested that in addition to the optical emissions from electron-impact excited electronic states of N 2 , a substantial portion of the spectrum may be due to chemiluminescent processes derived from vibrational kinetics of nitrogen.

Plasma Chemistry of Sprite Streamers

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

Discharges in the Stratosphere and Mesosphere

From June 2008 to January 2016 nearly 800 elves have been recorded by a low-light camera in northeastern Spain. Elves occur in this region mainly over the lower topped cold air mass maritime thunderstorms, peaking from November to January. Cloud-to-ground strokes still produce elves when maritime winter storms are carried inland, suggesting that the cold season thunderstorm charge configuration favors strokes with large electromagnetic pulses. Altitudes of 389 elves were determined using optical data combined with a lightning location network. The overall median altitude was 87.1 km, near the typical OH airglow height, but average heights during individual nights ranged between 83 and 93 km. The lower elve nights (~84 km) occurred during slightly elevated geomagnetic conditions (Kp >3-, Ap-index >10). Elve altitude often shifts by several kilometers during the night, apparently in response to changing background conditions in the upper mesosphere.

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Statistics and variability of the altitude of elves

Wave-like substorm arc features in the aurora and Pi2 magnetic disturbances observed in the near-Earth plasma sheet are frequently, and sometimes simultaneously, observed around the substorm onset time. We perform statistical analyses of the THEMIS ASI auroral observations that show wave-like bright spot structure along the arc prior to substorm onset. The azimuthal mode number values of the wave-like substorm arcs are found to be in the range of ~100–240 and decrease with increasing geomagnetic latitude of the substorm auroral arc location. We suggest that the azimuthal mode number is likely related to the ion gyroradius and azimuthal wave number. We also perform correlation study of the pre-onset wave-like substorm arc features and Pi2 magnetic disturbances for substorm dipolarization events observed by THEMIS satellites during 2008–2009. The wave-like arc brightness structures on the substorm auroral arcs tend to move azimuthally westward, but with a few exceptions of eastward movement, during tens of seconds prior to the substorm onset. The movement of the wave-like arc brightness structure is linearly correlated with the phase velocity of the Pi2 δB
 y
 disturbances in the near-Earth plasma sheet region. The result suggests that the Pi2 transverse δB
 y
 disturbances are related to the intensifying wave-like substorm onset arcs. One plausible explanation of the observations is the kinetic ballooning instability, which has high azimuthal mode number due to the ion gyroradius effect and finite parallel electric field that accelerates electrons into the ionosphere to produce the wave-like arc structure.

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Relationship between wave-like auroral arcs and Pi2 disturbances in plasma sheet prior to substorm onset

. We present synoptic observations of the 21 December 2006 substorm event by the THEMIS ground-based All-Sky-Imagers, the ISUAL CCD Imager aboard the FORMOSAT-2 satellite, the geosynchronous satellites and the ground-based magnetometers, and discuss the implication of the observations. There are three subsequent arc breakups with time separation of

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Behavior of substorm auroral arcs and Pi2 waves: implication for the kinetic ballooning instability

[1] This is the first report of the most comprehensive 630.0 nm airglow limb images taken using Imager of Sprites and Upper Atmospheric Lightnings (ISUAL) onboard FORMOSAT-2. The limb scans reveal two distinct airglow layers: the upper one corresponds to the thermospheric O(1D) emission and the lower one corresponds to the OH (9–3) emissions. Sequences of such observations are combined to generate altitude-latitude maps of the emissions, which reveal intensity enhancements of both the layers at certain locations where they often appear to be linked/joined vertically. A detailed analysis of the location and occurrence of the enhancements in the entire observations, together with simulations of the emissions suiting the ISUAL limb geometry are carried out to understand the causes and related processes.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2009JA014087

First results of the limb imaging of 630.0 nm airglow using FORMOSAT-2/Imager of Sprites and Upper Atmospheric Lightnings

[1] A previous study of lightning-induced transient emissions in and below the OH airglow layer using observations by the Imager of Sprites and Upper Atmospheric Lightning (ISUAL) CCD camera onboard the FORMOSAT-II satellite showed that intensity enhancements occurred more frequently in the OH airglow layer. Here we show the results of new observations made in December 2009 and January 2010 using a narrowband 630 nm filter and spectrophotometer and present further analysis. We estimated the N 2 1P intensity enhancements to be ~65% and 53% of the total intensity enhancements for the two events we analyzed using ISUAL and the spectrophotometer data in conjunction with a model for emissions of light and VLF perturbations from electromagnetic pulse sources (elves). Our analysis indicates that there is still somewhat considerable intensity enhancement (~1.25 kR) unaccounted for after the N 2 1 P contribution has been removed. Our study suggests that there might be OH emissions in elves and that OH species might also be involved in the lightning-induced process and contribute to the intensity enhancements that we observed.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2010JA015558

Further investigations of lightning‐induced transient emissions in the OH airglow layer

We report observations of lightning‐induced transient emissions (LITEs) in or below the OH airglow layer observed from the Imager of Sprites and Upper Atmospheric Lightning (ISUAL) onboard the FORMOSAT‐II satellite The ISUAL team conducted a nine‐day campaign in January 2007 using both the broadband and narrowband filters on the CCD imager It is found that LITEs occur more frequently in the OH airglow layer than below It is also found that the observations of LITEs below the OH airglow layer by the narrow‐band filter are rare The observations of LITEs by the narrowband filter are the first of its kind in existence Our data analysis shows that there is a significant intensity increase in the OH airglow layer when there is lightning and a residual intensity increase post the lightning activity We propose that LITEs in the OH airglow layer could be due to OH species

Chih-Yu Chiang

Papers

Behavior of substorm auroral arcs and Pi2 waves: implication for the kinetic ballooning instability

First results of the limb imaging of 630.0 nm airglow using FORMOSAT-2/Imager of Sprites and Upper Atmospheric Lightnings

Further investigations of lightning‐induced transient emissions in the OH airglow layer

Investigations of lightning-induced sudden brightening in the OH airglow layer observed by ISUAL onboard FORMOSAT-II satellite

Retrieval of Airglow Emission Rates in Analytical Form for Limb-viewing Satellite Observations at Low Latitudes