[1] We examine narrowband VLF observations and investigate the association of early VLF perturbations with gigantic jets recorded by the Imager of Sprites and Upper Atmospheric Lightnings (ISUAL) instrument aboard FORMOSAT-2. From its inception in 2004 to April 2013, the ISUAL instrument has recorded 90 gigantic jets using a triggered camera. Stanford VLF receivers located around the world are used to detect perturbations to VLF transmitter signals associated with lightning. While nine gigantic jet events occurred within 100 km of a VLF transmitter-receiver great circle path, only four early VLF events were detected in association with three ISUAL gigantic jets. One of these is a moderate event of 0.4 dB amplitude change, and the others are very small. The recovery time of these events are less than a couple of minutes and so do not constitute the “long recovery” early VLF events that have been postulated to be associated with gigantic jets. We speculate on possible explanations for the lack of other events on monitored paths, including a lack of significant ionization produced in the D region ionosphere by the gigantic jet event, weak transmitter signals recorded by the receivers, or mode effects on transmitter paths.
We find the conditions on the parameters of the ten parameter Poincaré gauge theory of gravity which allow solutions with 'asymptotically Newtonian' symmetry and fall off.
We study the post-Newtonian limit of a generalized dilaton gravity in which gravity is coupled to dilaton and eletromagnetic fields. The field equations are derived using the post-Newtonian scheme, and the approximate solution is presented for a point mass with electric and dilaton charges. The result indicates that the dilaton effect can be detected, in post-Newtonian level, using a charged test particle but not a neutral one. We have also checked that the approximate solution is indeed consistent with the weak field expansion of charged dilaton black hole solution in the harmonic coordinate.
Abstract The major types of transient luminous events (TLEs) are believed to be directly triggered by cloud‐to‐ground discharges. Intense lightning generally seems to have a higher production efficiency for TLEs, but this observation has not yet been statistically investigated. Two data sets, the upgraded World Wide Lightning Location Network (WWLLN) lightning stroke data and the Imager of Sprites and Upper Atmospheric Lightning (ISUAL) TLE data, were used to investigate the energetics and the geographic distribution of TLE‐producing lightning. The global median energy of the strokes that produced the TLEs is at least an order of magnitude higher than the global median stroke energy for WWLLN lightning in the same data window. Furthermore, the energy distributions of the elve‐producing strokes exhibit no oceanic and land disparity. These results reveal that the elves are indeed triggered by energetic lightning and the production efficiency of elves with respect to the stroke energy of the causative lightning was insensitive to the underlying landform. Analysis of the spatial correlation between the ISUAL elves and the WWLLN lightning reveals that the geographic distribution of the ISUAL elves agreed well with that for the most energetic 10% of the WWLLN lightning strokes, better than for total lighting. We also found that elve occurrence rates in the apparently reduced detection regions behind the Earth's limb may have been greatly underestimated, partially due to the failure in providing triggers to initiate ISUAL recording or the severity of atmospheric attenuation to the elve emissions that may have caused them to be undetected.
Abstract Sensitive long‐wavelength radar observations of absolute velocity never previously published from Jicamarca are brought to bear on the long‐standing problem of radar detection of slow‐moving meteors. Attention is devoted to evaluating the ionization coefficient β ( V ) in the critically important velocity range of 11–20 km/s in recent laboratory measurements of Thomas et al. (2016). Theoretical predictions for β ( V ) based on the laboratory data, on Jones (1997), on Janches et al. (2014), and on Verniani and Hawkins (1964) are used to correct the incoming meteor velocities measured with the sensitive Jicamarca high‐power, large‐aperture radar operating at 6 m wavelength. All corrected distributions are consistent with the predictions of the Nesvorný model in showing pronounced monotonic increases down to the escape velocity (11 km/s). Such distributions may be essential to explaining the pronounced ledge in nighttime electron density and the rapid disappearance of electrons in meteor trails in the altitude range of 80–85 km.
Abstract The blue luminous events (BLEs) recorded by ISUAL (Imager of Sprites and Upper Atmospheric Lightning) radiate unambiguous middle ultraviolet to blue emissions (230–450 nm) but contain dim red emissions (623–754 nm). The BLE appears to be dot‐like on one ISUAL image with an integration time of 29 ms. A few BLEs develop upward into blue jets/starters or type II gigantic jets (GJs). The associated sferics of the BLEs in the extremely low frequency to very low frequency band and in the low‐frequency band exhibit similar patterns to the narrow bipolar events (NBEs) identified in the very low frequency and low‐frequency band. The ISUAL BLEs are conjectured to be the accompanied light emissions of the NBEs. Both upward and downward propagating current obtained from the associated sferics of the BLEs have been found. The source heights of the six BLEs related to negative NBEs are estimated in the range of 16.2–17.8 km. These six events are suggested to occur between the upper positive charge layer and the negative screen charge layer on the top of the normally electrified thunderstorm. The six blue starters, one blue jet, and one type II GJ are inferred to be positive upward discharges from their associated sferics in the extremely low frequency to very low frequency band. Based on the simultaneous radio and optical observations, a NBE is conjectured to be the initiation discharge with rapidly flowing current within the thunderstorm, while a blue jet/starter or a type II GJ is suggested to be the ensuing discharge with slowly varying current propagating upward from the thunderstorm.
We find plane-fronted torsion waves propagating in the metrically flat spacetime in a gravitational gauge theory formulated in a Riemann-Cartan spacetime with Lagrangian ${R}_{\mathrm{ij}}{R}^{\mathrm{ij}}\ensuremath{-}\frac{1}{3}{R}^{2}$.
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