Sprite Discharges Research Articles

Possible direct cloud-to-ionosphere current evidenced by sprite-initiated secondary TLEs

[1] Video-rate images of sprites observed from Langmuir Laboratory show slow, upward discharges from the cloud to the mesosphere following the sprite discharge. A single high-time-resolution (1000 fps) measurement of the tip of the upward discharge shows that it terminates at the base of the preceding sprite and persists for a total of ∼50 ms, compared to the sprite lifetime of ∼6 ms. Photometer data show that these events are likely to be predominantly blue. We propose a mechanism by which, in conjunction with intra-cloud activity following the causative CG discharge, charge is moved within the sprite body from the ionosphere to the lower altitude edge of the sprite at ∼50 km; this transfer of charge lowers the upper capacitive plate, whereupon a second breakdown is facilitated between the cloud-top and this charged plate, inducing electrical current between the cloud and the mesosphere and initiating the observed luminous discharges.

The contribution of sprites to the global atmospheric electric circuit

Abstract The global static electric field in the global atmospheric electric circuit resulting from mesospheric sprite discharges is inferred from a coupled model for the global static and dynamic electric fields derived from Maxwell’s equations. It is found that the global atmospheric electric field from individual sprites is ≲ 44 mV/m, which can be measured with conventional ULF/ELF radio wave antennas at frequencies ≲ 4 Hz.

Subionospheric VLF perturbations associated with lightning discharges

The use of very-low frequency (VLF) transmissions propagating inside the waveguide formed by the Earth and the lower ionosphere is a well developed technique for probing conditions within the waveguide. This paper seeks to review the current understanding of lightning discharge associated processes that lead to changes in the characteristics of the waveguide and thus variations in the received phase and/or amplitude of VLF transmissions. Particular emphasis is placed upon events which appear to be produced directly by lightning discharge processes. These include VLF sprites and early Trimpi for which significant research efforts have been made over the last 10 years. The properties and interpretation of these events are discussed in detail. QE-field produced early Trimpi are due to relatively large disturbed regions (horizontal extent ∼100 km ) in the lower ionosphere. VLF sprites are produced by red sprite discharges, leading to relatively small, dense, ionospheric modifications made up of fine-scale horizontal structures (∼300 m) that stretch over wide altitude ranges (⩽50– 80 km ). Differences in the ionospheric modifications electron temperatures and ionisation structure produces the differing delay times and scattering patterns in the experimentally observed VLF perturbations. Lightning-EMP produced Elves lead to large (∼500 km) , relatively smoothly varying ionospheric disturbance at high altitudes (∼85 km) . Such a modification should create sudden step-like changes in received VLF amplitude and phase that lack a clear relaxation signature and occur along narrow forward-scattered directions. The VLF techniques described in this article are part of the larger field of research into high-altitude processes connected with thunderstorms. Lightning EMP produces a large (∼500 km) , relatively smoothly varying ionospheric disturbance at high altitudes (∼85 km) .

1439 Particle Simulation of Sprite Discharge in Upper Atmosphere

The paper presents a particle simulation method to study the sprite discharge in upper atmosphere. The particle simulation is used in combination with the quasi-electrostatic field calculation. The microscopic particle dynamics such as various collisions between electrons and neutral particles, involving elastic, excitation, ionization, attachment, and photoionization, are considered. The simulation results reveal the temporal evolution of particle dynamics and optical emissions during sprite discharges, providing the important theoretical basis for the study of sprite discharges.

Sprite observations in the Northern Territory of Australia

Sprites, a form of brief luminous discharge in the upper atmosphere above a thunderstorm, were observed and imaged on two video cameras in Australia's Northern Territory. These were the first such ground‐based observations made outside the United States. Sprite discharges typically took place between the altitudes of 50 km and 80 km and spanned an average width of 44 km. Many of the sprite events were of long duration, with an average of 145 ms. These spatial and temporal features were similar to those observed from the ground and the air in the United States. During the longer events, some luminous discharge elements were observed to decay as other new elements formed. As the new elements were often laterally displaced from the old, the sprites sometimes appeared to dance across the sky. This phenomenon has been observed in Colorado and named “dancing sprites.” The lateral progression of sprite elements observed in the Northern Territory was overwhelmingly in one direction and covered distances of up to 90 km.

On the temporal evolution of red sprites: Runaway theory versus data

The results of numerical simulations of red sprite discharges, namely the temporal evolutions of optical emissions, are presented and compared with observations. The simulations are done using the recently recalculated runaway avalanche rates. The temporal evolution of these simulations is in good agreement with ground‐based photometer and CCD TV camera observations of red sprites. Our model naturally explains the ‘hairline’ of red sprites as a boundary between the region where the intensity of optical emissions associated with runaway breakdown has a maximum and the region where the intensity of optical emissions caused by conventional breakdown and ambient electron heating has a maximum. Other important characteristics of the simulated sprite such as color, shape, altitude, and intensity are in agreement with the observations as well. We also present for the first time simulations of red sprites with a daytime conductivity profile.