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Subtle structure of streamers under conditions resembling those of Transient Luminous Events

Błęcki J. S., Mizerski K. A.

Archives of Mechanics

2018

Vol. 70, nr 6

535--550

The paper presents a brief review of the observational facts related to plasma filamentation in astrophysics and the subtle structures of plasma in Transient Luminous Events (TLE’s) and an analysis of the physical mechanism that could contribute to formation of filaments in plasma inside streamers. The values of physical parameters are assumed such as to resemble the physical conditions in streamers of the TLE’s. Estimates of the typical spatial scales of these structures and temporal characteristics of filament formation are given. The analysis concerns a non-magnetic mechanism based on a form of non-relativistic dissipative instability and the electron-nitrogen collisional 2Πg resonance. It is argued that the influence of the magnetic field is negligible at the leading order at least up to the altitudes of about 65–70 km. Under the conditions related to those in plasma inside the TLE’s, derived based on the current knowledge of physical parameters within the electric discharges, the identified dissipative-resonant instability is demonstrated to be the only/most vigorous linear instability developing in the system. It results in periodic plasma density distribution in the direction transverse to the electric field. The obtained time scales of the instability development are quick and proportional to the inverse of the ion-neutral collision frequency, 1/νi, whereas the proposed spatial scale of the density stripes/filaments is proportional to the electron temperature and inversely proportional to the speed of the discharge.

A Study of Early/Slow VLF Perturbations Observed at Agra, India

Pandey U., Singh A. K., Singh O. P., Singh B., Saraswat K.

Acta Geophysica

2016

Vol. 64, no. 3

755--771

We present here the results of sub-ionospheric VLF perturbations observed on NWC (19.8 kHz) transmitter signal propagating in the Earth-ionosphere waveguide, monitored at our low latitude station Agra. During the period of observation (June-December 2011), we found 89 cases of VLF perturbation, while only 73 cases showing early character associated with strong lightning discharges. Out of 73 events, 64 (~84%) of the early VLF perturbations are found to be early/slow in nature; the remaining 9 events are early/fast. The onset duration of these early/slow VLF perturbations is up to ~ 5 s. A total of 54 observed early events show amplitude change lying between ± 3.0 dB, and phase change ± 12 degree, respectively, and found to occur mainly during nighttime. One of the interesting results we found is that the events with larger recovery time lie far away from the VLF propagation path, while events with smaller duration of recovery are within the ± 50-100 km of signal path. The World Wide Lightning Location Network (WWLLN) data is analysed to find the location of causative lightning and temporal variation. The lightning discharge and associated processes that lead to early VLF events are discussed.