Criteria for sprites and elves based on Schumann resonance observations (original) (raw)
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Criteria for Elves and Sprites on Schumann Resonance Observations
1999
Ground flashes with positive polarity associated with both sprites and elves excite the Earth\u27s Schumann resonances to amplitudes several times greater than the background resonances. Theoretical predictions for dielectric breakdown in the mesosphere are tested using ELF methods to evaluate vertical charge moments of positive ground flashes. Comparisons of the measured time constants for lightning charge transfer with the electrostatic relaxation time at altitudes of nighttime sprite initiation (50–70 km) generally validate the electrostatic assumption in predictions made initially by Wilson [1925]. The measured charge moments (Q dS = 200–2000 C-km) are large in comparison with ordinary negative lightning but are generally insufficient to account for conventional air breakdown at sprite altitudes. The measured charge moments, however, are sufficient to account for electron runaway breakdown, and the long avalanche length in this mechanism also accounts for the exclusive associati...
Sprite lightning heard round the world by Schumann resonance methods
Radio Science, 2007
Electromagnetic transients have been recorded at the Massachusetts Institute of Technology field station in West Greenwich, Rhode Island, coinciding with spriteproducing lightning flashes in northern Australia, at a distance of 16.6 Mm. Single-station Schumann resonance methods have been used to locate the parent lightning flashes and to evaluate their vertical charge moments. The charge moment thresholds for sprite production are consistent with similar measurements with identical methods made at considerably closer range ($2 Mm). The use of a uniform model for the Earth-ionosphere waveguide can produce systematic errors in the source-receiver distance, of the order of 1 Mm. Further analysis of the observations has shown an important role for the daynight asymmetry of the waveguide in causing the systematic error, by lending appreciable asymmetry to the short and long paths of propagation round the world.
Radio Science, 2008
The interpretation of experimental Schumann resonance data presented by Williams et al. [2007] is discussed. We demonstrate that time delay of the model ELF pulse is in excellent agreement with their records conditioned by the geometrical source-observer distance, thus suggesting the day-night transition in their paper being unnecessary. Besides, we show that the terminator effect could not be detected in their particular experiment owing to a long propagation path, a particular orientation of terminator, and the 'extremely red' spectra of the field source. [2] Since the pioneer work by Ogawa et al. [1966], Qbursts are used for global detection and location of powerful lightning discharges. A spectral technique was developed by Jones [1970a, 1970b] and used by Kemp and Jones [1971], Kemp [1971], Lazebny and Nickolaenko [1976], and Burke and Jones [1992]. Correct stroke location in the Schumann resonance (SR) band was verified and the accuracy was 1-2 Mm for global distances [Boccippio et al., 1998; Füllekrug et al., 2000]. The paper by Williams et al. [2007] (hereinafter referred to as Paper I) directly compares the red sprites observed in Australia with simultaneous Q-bursts recorded in the USA at a distance of 16.6 Mm. The authors demonstrate that ELF pulses are connected with red sprites by presenting convincing experimental data: these indicate the correct source-observer distance (SOD) with the above mentioned accuracy. [3] However, they are not satisfied with their results and try to attribute the SOD deviations to the impact of
Journal of Atmospheric and Solar-Terrestrial Physics, 2009
During the summer of 2005, transient luminous events were optically imaged from the French Pyré né es as part of the EuroSprite campaign. Simultaneously, extremely low frequency (ELF: 3-3000 Hz) and broadband very low frequency (VLF: 3-30 kHz) data were recorded continuously at two separate receivers in Israel, located about 3300 km from the area of the parent lightning discharges responsible for the generation of sprites. Additionally, narrowband VLF data were collected in Crete, at about 2300 km away from the region of sprites.
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.
Journal of Atmospheric and Solar-Terrestrial Physics, 2003
Waveform monitoring of ELF radio signals in the frequency range of 1-400 Hz have been carried out on a routine basis at Syowa station (69:0 • S, 39:6 • E in geographic coordinates), Antarctica since February, 2000. The main purpose of these observations is to monitor global lightning activity and to locate lightning-induced sprites and elves. The ELF observation system consisting of two search coil sensors (geomagnetic north-south (H) and east-west (D) sensors) was installed at a remote unmanned observatory in West Ongul Island located 5 km southwest from Syowa station. As a back up system, the same system was installed near Syowa station in East Ongul Island. Signals from these sensors were digitally sampled at 1000 Hz with a GPS time code. On July 4, 2000 during the STEPS (Severe Thunderstorm Electriÿcation and Precipitation Studies) 2000 campaign carried out over the Great Plains in the US, 57 sprite events were observed from Yucca Ridge Field Station (40:7 • N, 104:9 • W), Colorado, and 53 out of these sprite events had one-to-one correspondence to transient Schumann resonances (SR) detected at Syowa station. The waveforms of these SR are characterized by sharp initial pulses and following damped oscillations. The great circles representing the propagation paths are determined from the Lissojous plots of the H and D magnetic ÿeld data of the transient SR. It has been demonstrated that the minimum distance between the great circles and the locations of causative cloud-to-ground (CG) discharges is ∼240 km on average. It is thus concluded that the method to determine the propagation paths from Lissajous plots is extremely accurate when we use the Syowa ELF waveform data. Consequently, it would be possible to globally triangulate sprite-inducing CG locations by setting up at least one more observation site with the same system.
Geophysical Research Letters, 1996
Horizontal magnetic field variations in the frequency range of the Earth-ionosphere cavity resonances are observed at Silberborn, Germany, simultaneous with 19 sprite-associated lightning flashes in the midwestern United States, on July 15, 1995. The measured horizontal magnetic intensities are linearly related to the horizontal magnetic intensities of slow tails of radio atmospherics which were simultaneously recorded at Palmer Station, Antarctica. Enhancement of the Earth-ionosphere cavity resonances is verified by spectral analysis, and the measured arrival azimuths are in agreement with the expected orientation of the Poynting vector along the great-circle path. The estimated accuracy of the arrival azimuth determination is on the order of ±5°.
Total global lightning inferred from Schumann resonance measurements
Journal of Geophysical Research, 1998
Radiation with frequencies of 5-30 Hz is ducted between Earth's surface and ionosphere with little attenuation; at the lowest frequencies, waves travel several times around the Earth before losing most of their energy. Much of this radiation is produced by lightning. Here we assume that all of this radiation is produced by lightning, and attempt to invert the observed electric and magnetic fields to infer the global lightning activity. We show 10 days of inversions. For these 10 days, the inferred average rate of vertical charge transfer squared is only 1.7 10 s (C km)2/s. Other studies suggest that the root mean square moment change of a flash is about 166 Coulomb kilometers. If we naively assume that each of these flashes is composed of four equally sized strokes, then we conclude that our entire observed signal could be produced by only 22 flashes per second.
In the past few years, dramatic experimental evidence has emerged, showing that tropospheric lightning discharges modify the mesosphere and the lower ionosphere through heating and ionization, producing gamma-ray bursts and optical emissions known as red sprites, blue jets, and elves. These transient electrodynamic coupling processes may have long-term effects such as chemical changes, persistent heating of ionospheric electrons, and increased production of mesospheric and stratospheric nitrogen oxides (NO y ). In order to assess the regional and global effects of the intense electrodynamic coupling of thunderstorms to the middle atmosphere, the occurrence rate of Sprites needs to be known over large areas of the Earth. Since continuous optical monitoring of Sprite occurrence on large spatial scales is not practical, a continuous proxy indicator for Sprite occurrence is needed.