VLF observations of ionospheric disturbances in association with TLEs from the EuroSprite-2007 campaign (original) (raw)
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Broadband VLF measurements of lightning-induced ionospheric perturbations
2008
Very low frequency (VLF) electromagnetic pulses radiated by lightning are an effective tool for probing the D region ionosphere. We detect and measure the D region ionospheric disturbances caused by the strong lightning flash by analyzing the broadband VLF spectrum from lightning that occurred just before and after a nearby intense lightning discharge. Comparing the measured electron density changes to those from previous measurements and the theoretical expectations, we find the detected perturbations are consistent with the theoretically predicted ionization changes produced directly by the lightning electromagnetic pulse.
Applied Sciences, 2022
The lower ionosphere influences the propagation of electromagnetic (EM) waves, satellite and also terrestrial (anthropic) signals at the time of intense perturbations and disturbances. Therefore, data and modelling of the perturbed lower ionosphere are crucial in various technological areas. An analysis of the lower ionospheric response induced by sudden events during daytime-solar flares and during night-time-lightning-induced electron precipitation was carried out. A case study of the solar flare event recorded on 7 September 2017 and lightning-induced electron precipitation event recorded on 16 November 2004 were used in this work. Sudden events induced changes in the ionosphere and, consequently, the electron density height profile. All data are recorded by Belgrade (BEL) radio station system and the model computation is used to obtain the ionospheric parameters induced by these sudden events. According to perturbed conditions, variation of estimated parameters, sharpness and re...
Geophysical Research Letters, 2012
Observations show that intense +CG lightning discharges which trigger both an elve and a sprite are associated with long-lasting conductivity modifications in the upper D-region ionosphere. They are observed as strong perturbations in VLF signals propagating through the disturbed region, manifested as LOng Recovery Early VLF events (LORE), which can last up to 30 minutes. These same ionospheric modifications are also responsible for step-like changes, seen mostly in off-storm VLF transmissions, which offset signal levels even for longer times. The evidence suggests that when a very intense positive cloud to ground lightning stroke leads to an elve and a high altitude sprite, and possibly a sprite halo as well, there is production of long lasting elevations in electron density at VLF reflection heights that cause LOREs and severe effects on VLF propagation. The present results confirm past predictions and postulations that elves may be accompanied by long-lasting electron density perturbations in the lower ionosphere.
Earth, Planets and Space, 2013
The occurrence of short-timescale (∼1-100 s) perturbations (early VLF events) on four Very Low Frequency (VLF) transmitter signals (call signs: NWC, NPM, VTX, NLK), recorded at Suva (18.1 • S, 178.5 • E, L = 1.16), shows the most frequent occurrence on the NWC signal and least on the VTX. Daytime early/fast events on the NWC transmission are (0.2-0.5 dB) with only negative amplitude perturbations with comparatively lower recovery times (10-30 s) as compared with most nighttime events with amplitude perturbations of 0.2-1.5 dB and recovery times of 20-80 s. The WorldWide Lightning Location Network detected causative lightnings for 74 of 453 early VLF events out of which 54 (73%) were produced due to narrow-angle scattering, and by 20 (27%) due to wide-angle scattering. The recovery (decay) of the scattered amplitude of early/fast events on the NWC signal shows both exponential and logarithmic forms, but the linear correlation coefficient is better with a logarithm fit. The first observations of early/slow events in daylight propagation are presented. Initial results on early/fast events with unusually long recoveries (≥5 min) and strong perturbations (≥1 dB) indicate that they are mainly observed on the transmissions from NPM and NLK in the nighttime only, with rare occurrence on other transmissions. Such unusually long recovery of early/fast events may be associated with large ionic conductivity perturbations associated with gigantic jets.
Journal of Geophysical Research: Space Physics, 2009
TLEs are optically observed from the U.S. Langmuir Laboratory, while ELF/VLF waveform data are simultaneously recorded on board the Centre National d'Etudes Spatiales microsatellite DEMETER and on the ground at Langmuir. Analyses of ELF/VLF measurements associated with sprite events observed on 28 July 2005 and 3 August 2005 are presented. Conditions to trace back the wave emissions from the satellite to the source region of the parent lightning discharge are discussed. The main results concern: (1) the identification from a low Earth orbit satellite of the 0+ whistler signatures of the TLE causative lightning; (2) the identification of the propagation characteristics of proton whistlers triggered by the 0+ whistlers of the causative lightning, and the potential use of those characteristics; (3) recognition of the difficulty to observe sprite-produced ELF bursts in the presence of proton-whistlers; (4) the use of geographical displays of the average power received by the DEMETER electric field antennas over the U.S. Navy transmitter North West Cape (NWC) located in Western Australia to evaluate VLF transmission cones which explain the presence (28 July events) or the absence (3 August events) of propagation links between sferics observed at ground and 0+ whistlers observed on DEMETER; and (5) owing to electron-collisions, an optimum transfer of energy from the atmosphere to the ionosphere for waves with k vectors antiparallel, or quasi-antiparallel, to Earth's magnetic field direction.
Journal of Geophysical Research, 2008
Abstract[1] Transient luminous events above thunderstorms such as sprites, halos, and elves require large electric fields in the lower ionosphere. Yet very few in situ measurements in this region have been successfully accomplished, since it is typically too low in altitude for rockets and satellites and too high for balloons. In this article, we present some rare examples of lightning-driven electric field changes obtained at 75–130 km altitude during a sounding rocket flight from Wallops Island, Virginia, in 1995. We summarize these electric field changes and present a few detailed case studies. Our measurements are compared directly to a 2D numerical model of lightning-driven electromagnetic fields in the middle and upper atmosphere. We find that the in situ electric field changes are smaller than predicted by the model, and the amplitudes of these fields are insufficient for elve production when extrapolated to a 100 kA peak current stroke. This disagreement could be due to lightning-induced ionospheric conductivity enhancement, or it might be evidence of flaws in the electromagnetic pulse mechanism for elves.
Lightning-induced perturbations on VLF subionospheric transmissions
Journal of Atmospheric and Terrestrial Physics, 1990
Phase and amplitude perturbations on VLF subionospheric transmissions from transmitter NWC to Dunedin have been studied on both MSK frequencies and at spaced receivers, 9 km apart. In any one event (a 'Trimpi') the phase and amplitude perturbation can be expressed in terms of a perturbation phasor. This is generally believed to be the result of lightning-induced electron precipitation (LEP) producing a localized increase in ionization near the normal reflection height for subionospheric (waveguide) VLF waves. Most of the Trimpis received on the NWC-Dunedin path can be best explained if the LEP ionization is sufficiently localized so that it acts as a scattering centre for the subionospheric VLF wave from the transmitter. It is then this scattered wave or echo at the receiver which makes the perturbation phasor. We call these 'echo Trimpis'. The phase of the echo relative to the direct signal will differ on spaced antennae if the angle of arrival of the two signals differ. Similarly, this relative phase will vary with frequency if the group delay of the signals differ. Thus measurement of these differences allows location of the scattering centres, and so too the LEP. Locations made show a significant grouping in a region where the lightning intensity is high. This and other features strongly suggest that these echo Trimpis originate from local (southern hemisphere) lightning. This and other reasons are suggested to explain the high proportion of echo Trimpis on this path.
A study of sub-ionospheric early VLF perturbations observed at Agra (L=1.15), India
2014 XXXIth URSI General Assembly and Scientific Symposium (URSI GASS), 2014
In this paper, we present the results of sub-ionospheric VLF perturbations observed on NWC (19.8 kHz) ransmitter signal propagating in the Earth-ionosphere waveguide, monitored at Agra (Geomag. Lat 27˚E, long. 78˚N) using SoftPAL receiver. During the period of observation (June, 2011 to December, 2011), we found 75 cases of abrupt amplitude/phase perturbations showing early character. Most of the early events observed show an amplitude change lying between 0.16-4.5 dB, only few cases having >4.5 dB and phase change lying between 01-17 degree respectively. The onset duration of these early perturbations is up to ~ 5 sec, showing early slow character. The World Wide Lightning Location Network (WWLLN) data and the broadband VLF data is analysed to find the location of causative lightning associated with these early VLF perturbations. During the period of our study majority of the events are observed at nighttimes and only few cases are observed at daytimes most likely due to the occurrence of red sprite or elves in the daytime. The lightning discharge and associated processes that leads to the changes in the waveguide characteristics and hence VLF transmission have been discussed. .
Journal of Geophysical Research: Space Physics, 2007
Prompt early/fast perturbations on narrowband sub-ionospherically propagating very low frequency (VLF) signals are the primary evidence for the direct coupling of energy released by lightning discharge to the lower ionosphere. Different mechanisms have been advanced to explain the fast ionospheric perturbations, such as heating and ionization from the lightning electromagnetic pulse (EMP) associated with elves or from quasielectrostatic fields associated with sprites and halos. By comparing the broadband VLF spectra (3-25 kHz) of lightning discharges that shortly followed high peak current lightning discharges with the spectra of lightning discharges that did not, we detect D region perturbations caused by these intense lightning strokes over the U.S. East Coast and the U.S. High Plains. The electron density changes are measured by analyzing the broadband VLF propagation changes, and the perturbed electron density profiles from both regions are found to be consistent with those theoretically predicted for strong lightning EMP. In one case, a D region perturbation was detected following a lightning stroke that produced an isolated elve recorded by the Imager of Sprites and Upper Atmospheric Lightning (ISUAL) instrument on the FORMOSAT-2 satellite, confirming the EMP origins of these ionospheric perturbations. For this case, we measure electron density enhancements of 460 cm À3 averaged over a 220-km radius and 10-km-high perturbation region, in good agreement with the 210 cm À3 measured optically by Mende et al. (2005) for a different elve event. The characteristics of the lightning responsible for these ionospheric perturbations are investigated by comparing high peak current lighting strokes that do and do not generate detectable ionospheric perturbations.