VLF Observation of Long Ionospheric Recovery Events
01 Dec 2006-Vol. 2006
TL;DR: In this article, a new class of early/fast VLF events with recoveries of up to 20 min was introduced, much longer than typical Early/fast and Lightning-induced Electron Precipitation (LEP) events which recover to pre-event levels in ≲200 s.
Abstract: [1] We introduce a new class of Early/fast VLF events with recoveries of up to 20 min, much longer than typical Early/fast and Lightning-induced Electron Precipitation (LEP) events which recover to pre-event levels in ≲200 s. Three distinct types of long recovery events are observed, each exhibiting different characteristics, with the observed features of at least some of the event types consistent with the possibility of persistent ionization at altitudes below 60 km as put forth by Lehtinen and Inan (2007).
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Dissertation•
01 May 2017
Abstract: Title: The Effects of Thunderstorm Static and Quasi-Static Electric Fields on the Lower Ionosphere Author: Mohammad Ahmad Salem Major Advisors: Hamid K. Rassoul, Ph.D. and Ningyu Liu, Ph.D. Thunderstorms and their lightning discharges are of great interest to many areas of geophysics and atmospheric electricity. A thunderstorm is an electric generator; it can produce both electrostatic and quasi-electrostatic fields in the overhead atmospheric D region. The D region is the lower part of the ionosphere that extends from about 40-90 km altitude where the electrons and ions are sufficient enough to affect the propagation of radio waves. In contrast to the electrostatic field, the quasi-electrostatic fields can be much stronger in magnitude, but shorter in duration, and can trigger halos. A halo is one type of the transient luminous events (TLEs) and typically appears within 1-2 ms after an intense cloud to ground lightning discharge. It looks like a relatively homogeneous glow in the shape of a pancake that is centered around 75-80 km altitude with a horizontal extent of tens of kilometers and vertical thickness of several kilometers. The goals of this dissertation research are to investigate the electrical effects of thunderstorm electrostatic and quasi-electrostatic fields on the nighttime lower ionosphere, and their covert relation to the formation of atmospheric halos. This work entails numerical and theoretical modeling analyses, and comparison of current theory and simulation results with the actual observations. iii For the first part of this study we have demonstrated that, under steady state conditions, electrostatic fields of <0.4Ek values (not strong enough to produce TLEs) can be established in the lower ionosphere due to underlying thunderstorms. We utilized the simplified nighttime ion chemistry model described in the work of Liu [2012] to investigate how these fields affect the lower ionosphere ion density profile. The three-body electron attachment, through which electrons can be converted to negative ions, is the only process whose rate constant depends on the field values within the above-mentioned limit. As a result of the variation of the rate constant with the electric field, the nighttime steady state electron density profile can be reduced by ∼40% or enhanced by a factor of ∼6. We have improved our model in order to self-consistently calculate the steady state conductivity of the lower ionosphere above a thunderstorm. The new model takes into account the heating effects of thunderstorm electrostatic fields on the free electrons. The modeling results indicate that under steady state condition, although the electron density is generally increased, the nighttime lower ionospheric conductivity can be reduced by up to 1-2 orders of magnitude because electron mobility is significantly reduced due to the electron heating effect. Because of this reduction, it is found that for a typical ionospheric density profile, the resulting changes in the reflection heights of ELF and VLF waves are 5 and 2 km, respectively. In the second part of this dissertation, a one-dimensional plasma discharge fluid model is developed to study the response of the nighttime lower ionosphere to the quasi-electrostatic field produced by cloud-to-ground lightning flashes. When the quasi-electrostatic field reaches and exceeds about Ek, a halo can be triggered in the lower ionosphere. The modeling results indicate that the ionospheric perturbation is determined by the ambient ionospheric density profile, the charge
3 citations
Cites background from "VLF Observation of Long Ionospheric..."
...When these perturbations are caused by lightning discharges, they are known as “Early VLF” perturbations or events [Cotts and Inan, 2007], indicating the direct coupling between the lower and the upper atmospheres....
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..., 1993, 2010], but long recovery timescale up to tens of minutes has also been observed [Cotts and Inan, 2007]....
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DOI•
01 May 2022
TL;DR: In this article , an artificial neural network was constructed to detect and label early/fast events. But the authors did not find evidence that long-recovery events are a distinct class of early/Fast events.
Abstract: The analysis of very low frequency (VLF, 3–30 kHz) radio scattering can be used to measure the impact of lightning on the D region of the ionosphere (60–90 km). Early/fast events are prompt and rapid changes to the D‐region ionosphere associated with certain lightning flashes, causing heating, ionization, and attachment. Previous work has observed the behavior of early/fast events and their connection to specific types of lightning flashes through VLF remote sensing and lightning geolocation, but the unique nature of each event makes it difficult to broadly infer the interactions between lightning and the ionosphere using a small number of case studies. We assembled a massive database of VLF amplitude samples for cases when high‐intensity lightning occurs near a transmitter‐receiver path. We constructed an artificial neural network to detect and label early/fast events. With a large volume of events compiled, we charted detailed statistics of event occurrences and behavior. We find a correlation between lightning current magnitude and event likelihood, as well as inverse correlation between event likelihood and distance to transmitter‐receiver path. We further confirm the asymmetry of the peak current trends, with positive‐current strokes being significantly more likely to produce an event. We find that increased distance of the lightning to the transmitter, and to a lesser extent to the receiver, decreases the probability of an ionospheric disturbance. We find that recovery time is largely not a function of the peak current. We do not find evidence that long‐recovery events are a distinct class of Early/Fast events.
2 citations
DOI•
16 Mar 2023
TL;DR: In this article , the relationship between the energy of lightning strokes and the level of VLF perturbation was studied using the World Wide Lightning Location Network data, for the first time.
Abstract: The subionospheric early very low frequency (VLF) perturbations observed on NWC (19.8 kHz) navigational transmitter signal monitored at a low‐latitude station, Suva (18.1°S, 178.5°E), Fiji, during campaign periods of November 2011, 2012, and 2014 and December 2014, are presented. Early VLF events are associated with D‐region conductivity changes mainly produced by lightning‐generated transient luminous events (TLEs). Early VLF events occurred both during daytime and nighttime, with a considerably higher occurrence at nighttime. VLF perturbations caused by lightning strokes located up to 100 km off the transmitter‐receiver great circle path (TRGCP) are attributed to narrow‐angle scattering, while lightning strokes 100–500 km off the TRGCP are considered to cause early VLF events by wide‐angle scattering. Using the World Wide Lightning Location Network data, for the first time, we have studied the relationship between the energy of lightning strokes and the level of VLF perturbations. Greater is the energy of lightning, greater would be the strength of the VLF perturbation. However, the low‐energy lightning stroke can also produce a comparable level of perturbation to that of strong lightning. The modeling results of scattered amplitude (M) and echo phase (ϕE) of the unusually long recovery early/fast VLF event showed a better exponential fit (r ∼ 0.9) than the logarithmic fit. Long‐wavelength propagation capability (LWPC) code modeling of nighttime early VLF events considering causative TLE width of 50 km column indicated a decrease in the D‐region reference height (Hʹ) by up to 30 km and an increase in the sharpness factor (β) by 0.25 km−1.
27 Apr 2023
TL;DR: In this paper , the amplitude perturbations of a VLF transceiver signal are characterized as either long-recovery, early events (LOREs) or as early events.
Abstract: Electromagnetic pulses (EMPs) and quasi‐static electric fields (QE) from powerful lightning heat and ionize the lower ionosphere. The EMP disturbance may appear as an elve at ∼80–95 km altitude, and the QE field as a halo or a sprite at ∼60–80 km altitude. Both are thought to perturb crossing radio signals because of changes to the electrical conductivity of the regions. Here we present an analysis of 63 elves and corresponding radio signal perturbations from an almost stationary thunderstorm system that allows us to untangle some of the dependencies of perturbations on the lightning characteristics. The amplitude perturbations of a VLF‐transmitter signal are characterized as either long‐recovery, early events (LOREs) or as early events. We find that LOREs are related to lightning with high peak currents and bright elves, and that their sign (amplitude increase or decrease) depends on the relative locations of the transmitter, disturbance and receiver. Based on a subset of strokes, lightning with elves has on average ∼3 times the impulse charge‐moment‐change and power in broadband as lightning of similar peak currents without elves. The early events occur without observed elves, sprites or halos. They recover in ∼10–100 s and are observed for both polarities of cloud‐to‐ground lightning and for intracloud flashes. It is proposed that these observations may relate to regions of reduced conductivity caused by an electron attachment/detachment process at lower heights, or by electron enhancements associated with TLEs that are too dim to be detected by the camera.
TL;DR: In this article , columniform sprites and associated gravity waves (GWs) were observed using the Transient Luminous Events (TLEs) camera and All-sky imager at Prayagraj (25.5° N, 81.9° E, geomag. lat.
Abstract: We report rare simultaneous observations of columniform sprites and associated gravity waves (GWs) using the Transient Luminous Events (TLEs) camera and All-sky imager at Prayagraj (25.5° N, 81.9° E, geomag. lat. ~ 16.5° N), India. On 30 May 2014, a Mesoscale Convective System generated a group of sprites over the north horizon that reached the upper mesosphere. Just before this event, GWs (period ~ 14 min) were seen in OH broadband airglow (emission peak ~ 87 km) imaging that propagated in the direction of the sprite occurrence and dissipated in the background atmosphere thereby generating turbulence. About 9-14 min after the sprite event, another set of GWs (period ~ 11 min) was observed in OH imaging that arrived from the direction of the TLEs. At this site, we also record Very Low Frequency navigational transmitter signal JJI (22.2 kHz) from Japan. The amplitude of the JJI signal showed the presence of GWs with ~ 12.2 min periodicities and ~ 18 min period. The GWs of similar features were observed in the ionospheric Total Electron Content variations recorded at a nearby GPS site. The results presented here are important to understand the physical coupling of the troposphere with the lower and upper ionosphere through GWs.
References
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Book•
01 Jan 1998
TL;DR: In this article, the authors present an overview of the electrical properties of the Earth's atmosphere and discuss the effect of electricity on cloud microphysics, including electricity and magnetism.
Abstract: Tutorial: Basic Electricity and Magnetism 1. Overview of the Electrical Nature of the Earth's Atmosphere 2. Electrified Non-Thunderstorm Clouds 3. Introduction to the Electrical Nature of Thunderstorms 4. Corona and Point Discharge 5. Lightning 6. Instruments 7. Observations of the Electrical Characteristics of Thunderstorms, Part 1 8. Observations of the Electrical Characteristics of Thunderstorms, Part 2 9. Numerical Models of Thunderstorm Electrification 10. Electrical Effects on Cloud Microphysics
650 citations
"VLF Observation of Long Ionospheric..." refers background in this paper
...It is known, for example, that at stratospheric altitudes ( McGorman and Rust, 1998, section 1.4 ] and it is possible these long recoveries are due to processes at lower altitudes where ion chemistry typically becomes dominant....
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TL;DR: A 12-hour sequence of perturbations of subionospheric VLF signals observed in association with lightning provided preliminary evidence that the ionospheric regions perturbed in these events may be confined to within ∼150 km of the lightning discharges, and that intracloud flashes as well as cloud-to-ground lightning may be important in producing the perturbation.
Abstract: A 12-hour sequence of perturbations of subionospheric VLF signals observed in association with lightning provided preliminary evidence that the ionospheric regions perturbed in these events may be confined to within ∼150 km of the lightning discharges, and that intracloud flashes as well as cloud-to-ground lightning may be important in producing the perturbations. High-resolution analysis of event signatures indicated the presence of two different classes of events. For one set of events, observed during the most active central 6 hours of the observation period, a ∼0.6-s delay between the causative lightning and VLF event onset and a ∼1-s onset duration was observed, consistent with previously suggested models of the gyroresonant whistler-particle interaction that leads to particle precipitation and perturbation of the Earth-ionosphere waveguide. However, another set of events, observed during the first 2 hours of the observation period, exhibited a very different temporal signature, characterized by a much smaller (<50 ms) delay and sometimes also very short (<50 ms) rise times. Such events are possibly related to previously reported cases of similarly early/fast events and may involve a more direct coupling between the lightning discharge and the lower ionosphere.
122 citations
"VLF Observation of Long Ionospheric..." refers background or methods or result in this paper
...Published data contains examples of recoveries >200 s [e.g., Inan et al., 1988, Figure 17; Inan et al., 1996, Figure 6 (Event M); Dowden et al., 1997, Figure 2e], none of which were highlighted or noted as unusual....
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...This step-change behavior is similar to previous observations [e.g., Inan et al., 1988, Figure 17; Inan et al., 1996, Figure 6 (Event M)], and was predicted to sometimes occur by Glukhov et al. [1992] and Pasko and Inan [1994]....
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...They have long been observed [Inan et al., 1988] to occur within 20 ms of a causative lightning discharge, endure <20 ms [Inan et al., 1993; Dowden et al., 1994], and recover in 60–180 s [Sampath et al., 2000]....
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...They have long been observed [Inan et al., 1988] to occur within 20 ms of a causative lightning discharge, endure <20 ms [Inan et al....
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TL;DR: In this article, a quantitative model of the relaxation of transient lower ionospheric (D region) disturbances caused by lightning-induced electron precipitation is developed, taking advantage of known particular features of the lightning induced disturbances, such as the fact that they are produced in typically <1 s and decay over 10-100 s.
Abstract: A quantitative model of the relaxation of transient lower ionospheric (D region) disturbances caused by lightning-induced electron precipitation is developed, taking advantage of known particular features of the lightning-induced disturbances, such as the fact that they are produced in typically <1 s and decay over 10–100 s. The model represents the nighttime D region as consisting of only four kinds of charged particles (electrons, positive ions, negative ions, and positive cluster ions) and is particularly suited for description of the detailed behavior of the electron density. Application of the model to some previously modeled disturbances indicates that some of the least known chemical reaction rates in the nighttime D region altitudes may be measurable using subionospheric VLF data. In the production of secondary ionization by precipitating electron bursts, the model calculations indicate the presence of a saturation effect such that the number density of the secondary electrons is not simply equal to the ion pair production rate times the burst duration. In some cases involving precipitation of ∼1-MeV electrons, the model predicts the formation of new layers of ionization at 50–70 km altitude that represent a different attachment-detachment quasi-equilibrium value from that of the unperturbed ambient. Such new layers may exist for up to ∼105 s following electron precipitation bursts.
113 citations
"VLF Observation of Long Ionospheric..." refers background in this paper
...[16] Type 3 events are illustrated by Event D (Figure 3) where the amplitude response does not recover to pre-event levels, possibly because the atmosphere has attained a quasi-equilibrium state, the recovery from which takes a much longer time [Glukhov et al., 1992; Pasko and Inan, 1994]....
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TL;DR: In this paper, a transmitter in Silver Creek, Nebraska, propagating to Huntsville (HU), Alabama over a approximately 1200 km Great Circle Path (GCP) exhibit characteristic amplitude changes which appear within 20 ms of cloud-to-ground (CG) flashes located within 50 km of the path, consistent with the heating of ionospheric electrons by the electromagnetic pulse from lightning producing ionization changes in the D-region over the thunderstorm.
Abstract: 48.5 kHz signals from a transmitter in Silver Creek, Nebraska, propagating to Huntsville (HU), Alabama over a approximately 1200 km Great Circle Path (GCP) exhibit characteristic amplitude changes which appear within 20 ms of cloud-to-ground (CG) flashes located within 50 km of the path. Data are consistent with the heating of ionospheric electrons by the electromagnetic (EM) pulse from lightning producing ionization changes in the D-region over the thunderstorm.
97 citations
"VLF Observation of Long Ionospheric..." refers background in this paper
...They have long been observed [Inan et al., 1988] to occur within 20 ms of a causative lightning discharge, endure <20 ms [Inan et al., 1993; Dowden et al., 1994], and recover in 60–180 s [Sampath et al., 2000]....
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..., 1988] to occur within 20 ms of a causative lightning discharge, endure <20 ms [Inan et al., 1993; Dowden et al., 1994], and recover in 60–180 s [Sampath et al....
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TL;DR: In this paper, the authors reported the observation of short-duration VLF or LF perturbations, in which the amplitude of the subionospheric signal exhibits a sudden change within 20 ms of the causative lightning discharge, and recovers back to its original level in < 3 s.
Abstract: New evidence is presented of disturbances of the electrical conductivity of the nighttime mesosphere and the lower ionosphere in association with lightning discharges. In addition to extensive documentation of the characteristics of a class of events heretofore referred to as early/fast VLF events [Inan et al., 1993], our data reveal a new feature of these events, consisting of a postonset peak that typically lasts for 1–2 s. We also report the observation of short-duration VLF or LF perturbations, in which the amplitude of the subionospheric signal exhibits a sudden change within 20 ms of the causative lightning discharge, and recovers back to its original level in < 3 s. These short-duration events have characteristics similar to the previously observed rapid onset, rapid decay VLF signatures [Dowden et al.., 1994]. Both the typical and rapidly recovering events are observed primarily when the causative lightning discharge is within ±50 km of the VLF or LF great circle propagation path, indicating that the scattering from the localized disturbance is highly collimated in the forward direction. The latter in turn implies that for the parameters in hand, the transverse extent of the disturbance must be at least ∼ 100–150 km. The measured VLF signatures are compared with the predictions of a three-dimensional model of subionospheric VLF propagation and scattering in the presence of localized ionospheric disturbances produced by electromagnetic impulses and quasi-electrostatic (QE) fields produced by lightning discharges. The rapidly recovering or short-duration events are consistent with the heating of the ambient electrons by quasi-static electric fields, in cases when heating is not intense enough to exceed the attachment or ionization thresholds. When no significant electron density changes occur, the conductivity changes due to heating alone last only as long as the QE fields, typically less than a few seconds. When heating is intense enough so that attachment or ionization thresholds are exceeded, reductions or enhancements in electron density can respectively occur, in which case the medium would relax back to the ambient conditions with the time scales of the local D region chemistry, typically 10–100 s.
88 citations
"VLF Observation of Long Ionospheric..." refers methods or result in this paper
...Published data contains examples of recoveries >200 s [e.g., Inan et al., 1988, Figure 17; Inan et al., 1996, Figure 6 (Event M); Dowden et al., 1997, Figure 2e], none of which were highlighted or noted as unusual....
[...]
...This step-change behavior is similar to previous observations [e.g., Inan et al., 1988, Figure 17; Inan et al., 1996, Figure 6 (Event M)], and was predicted to sometimes occur by Glukhov et al. [1992] and Pasko and Inan [1994]....
[...]
...This step-change behavior is similar to previous observations [e.g., Inan et al., 1988, Figure 17; Inan et al., 1996, Figure 6 (Event M)], and was predicted to sometimes occur by Glukhov et al. [1992] and Pasko and Inan [1994]....
[...]