On the inception of streamers from sprite halo events produced by lightning discharges with positive and negative polarity

Abstract

[1] In the sprite halo events produced by cloud-to-ground lightning discharges, the spatial offsets, long delays, and polarity asymmetry related to the inception of sprite streamers are yet to be explained consistently with observations. In the present work, we use a two-dimensional model and a high-resolution one-dimensional plasma fluid model accounting for electron impact ionization, dissociative attachment, and photoionization processes to simulate halo events. In order to monitor the inception of sprite streamers, that cannot be modeled with present computer resources in the framework of fluid models, we use an improved avalanche-to-streamer transition criterion and investigate the response of the lower ionosphere to the charge moment changes induced by lightning discharges as a system of avalanches. On the basis of simulation results, we suggest a new mechanism for the inception of sprite streamers, explaining specifically how they can be triggered spatially outside of and temporally separated from the main sprite halo. The inception of sprite streamers is demonstrated to depend strongly on the charge moment change and the ambient electron density profile, which together determine the size of the streamer initiation region. We show that sprite streamers are mostly triggered by positive cloud-to-ground lightning discharges mainly because of mechanisms related to direction of propagation of electron avalanches. Moreover, the triggering of long-delayed sprites is demonstrated to be a unique property of halos produced by positive cloud-to-ground lightning discharges due to the formation of a long-lasting high-field region. Lightning continuing current can enlarge this high-field region and pull it down to lower altitudes where electron density is lower, extending the streamer initiation region.Citation: Qin, J., S. Celestin, and V. P. Pasko (2011), On the inception of streamers from sprite halo events produced by lightning discharges with positive and negative polarity,

Plasma irregularities in the D-region ionosphere in association with sprite streamer initiation

“…9). On the other hand, recent modelling studies indicate that the presence of plasma irregularities, previously thought not to be indispensable, is in fact a necessary condition for the initiation of sprite streamers 10,11 , in agreement with recent experimental findings showing that a large charge moment change is a necessary but not sufficient condition for sprites 12 . However, up to date, no solid evidence of D-region plasma irregularities in association with sprite streamer initiation has been presented, and if these irregularities exist their characteristics and origin(s) remain unknown.…”

“…A recently proposed theory suggests that the presence of strong plasma irregularities in the D-region ionosphere is a necessary condition for the initiation of sprite streamers 10,16 , and modelling results show that vertically elongated plasma columns are more favourable for streamer initiation when compared with spherical irregularities 17,18 . The above reconstructed images demonstrate for the first time solid evidence of kilometre-scale plasma irregularities in association with sprite streamer initiation in the D-region ionosphere.…”

“…In particular, in all halo events presented in this work, the electrons move upwards (that is, in an opposite direction to the downward movement of the halos) due to the positive polarity of the causative lightning discharges. The observed descent of a sprite halo as an entire object is due to the increase of the large-scale lightning electric field E at low altitudes and fast relaxation at high altitudes during the causative lightning discharge, leading to the lowering of the thin altitude region with large values of E/N, where N is the air density at the altitude of interest and E/N is referred to as the reduced electric field 10 . Note that large values of E/N lead to high rate of electron impact excitation of N 2 , which is the main physical process accounting for the halo optical emissions (that is, the large-scale halo is optical manifestation of the region of large reduced electric field in the lower ionosphere.)…”

Sprite streamer initiation from natural mesospheric structures

“…It has been found that streamers can be initiated from thin, dense column ionization patches with a plasma density more than three orders of magnitude, higher than the ambient ionospheric electron density 21,22 or from hundreds of metre wide spherical patches with a density about two orders of magnitude higher than the ambient value 25 . Modelling studies have also shown that plasma inhomogeneities with a density of two orders of magnitude higher than the ambient are also required for sprite streamer initiation at overbreakdown conditions 19,20,23 . The candidate sources of the inhomogeneities include the ionospheric effects of thunderstorm/lightning activities, meteor trails and gravity waves 21,22 , but no study has unambiguously demonstrated the feasibility of streamer initiation from the inhomogeneities created by any of those processes.…”

“…The propagation characteristics of a single sprite streamer, such as acceleration, expansion and brightening, are relatively well understood [10][11][12][13][14][15][16][17][18] . However, how sprite streamers are initiated, a critical question to understand the responses of the upper atmosphere to sudden, strong QE field impacts, is still under active debate 14,[19][20][21][22][23][24][25][26] .…”