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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]

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]

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]

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]

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]