Rare examples of early VLF events observed in association with ISUAL-detected gigantic jets
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[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.Keywords:
Narrowband
Lightning
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Schumann resonances
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A system for narrowband propagation measurements at 1700 MHz comprising a portable transmitter and two stationary receivers is presented. With this set-up, simulcast is used, and the receivers sample the same carrier frequency. The measured field-strength values are recorded in a laptop-type PC, together with information from the transmitter including sample number and location. The system allows investigation of propagation losses, shadowing due to body effects and different diversity schemes since the recorded values can be identified and compared owing to the transmitted information. The first results show how the fading statistics change when the person carrying the portable transmitter disturbs the radio path.< >
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A multifunctional solid-state transmitter is introduced in this paper.A few issues are discussed,including multifunctional requirements of the solid-state transmitter,different transmitter schemes,composition and principle of the solid-state transmitter modules,and key technical difficulties of the transmitter.Transmitting low sidelobe of active phased array radar antenna is a notable feature of the transmitter.Transmitting low sidelobe can be realized by using distributed,amplitude weighted transmitter modules.In order to integrate the functions,a series of engineering problems that should be solved in the process of the transmitter development are discussed in detail.Satisfying experimental results are given in the end.
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Critical frequency
Solar flare
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Profiling (computer programming)
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Certain transmitter adjustments are customarily made by optimizing performance as measured at the output of a visual demodulator. For reasons discussed in the text, demodulators used at the transmitter must have different design characteristics than typical home receivers. As a consequence, picture quality on the station monitor may be somewhat different than that seen on the average home receiver. The differences are described in the paper. Even if the transmitter were adjusted with typical receiver performance in mind, it is shown that the best transmitter adjustment for one receiver would not be the best for receivers designed with different selectivities and/or different envelope delays.
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Abstract Terrestrial Very‐Low‐Frequency (VLF) energy from both lightning discharges and radio transmitters has a role in affecting the energetic electrons in the Van Allen radiation belts, but quantification of these effects is particularly difficult, largely due to the collisional damping experienced in the highly variable electron density in the D‐ and E‐region ionosphere. The Faraday International Reference Ionosphere (FIRI) model was specifically developed by combining lower‐ionosphere chemistry modeling with in situ rocket measurements, and represents to date the most reliable source of electron density profiles for the lower ionosphere. As a full‐resolution empirical model, FIRI is not well suited to D‐ and E‐region ionosphere inversion, and its applicability in transionospheric VLF simulation and in remote sensing of the lower ionosphere is limited. Motivated by how subionospheric VLF remote sensing has been aided by the Wait and Spies (WS) profile (Wait & Spies, 1964), in this study, we parameterize the FIRI profiles and extend the WS profile to the E‐region ionosphere by introducing two new parameters: the knee altitude h k and the sharpness parameter for the E‐region ionosphere β E . Using this modified WS profile, we calculate the expected signals at different receiver locations from the NAA, NPM, and NWC transmitters under the full range of possible ionospheric conditions. We also describe and validate a method about how these results can be readily used to translate VLF measurements into estimates of the lower ionosphere electron density. Moreover, we use this method to evaluate the sensitivity of different ground receiver locations in lower‐ionosphere remote sensing.
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Abstract We introduce a method to diagnose and track the D region ionosphere (60–100 km). This region is important for long‐distance terrestrial communication and is impacted by a variety of geophysical phenomena, but it is traditionally very difficult to detect. Modern remote sensing methods used to study the D region are predominately near the very low frequency (VLF, 3–30 kHz) band, with some work also done in the high‐frequency and very high frequency bands (HF/VHF, 3–300 MHz). However, the frequency band between VLF and HF has been largely ignored as a diagnostic tool for the ionosphere. In this paper, we evaluate the use of 300 kHz radio reflections as a diagnostic tool for characterizing the D region of the ionosphere. We present radio receiver data, analyze diurnal trends in the signal from these transmitters, and identify ionospheric disturbances impacting LF/MF propagation. We find that 300 kHz remote sensing may allow a unique method for D region diagnostics compared to both the VLF and HF/VHF frequency bands, due to a more direct ionospheric reflection coefficient calculation method with high temporal resolution without the use of forward modeling.
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Radio spectrum
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Since earthquakes are seismic activities that various symptoms appear before they occur. One of the effects of seismic activity is known to be on the lower ionosphere layer. For this reason, changes on the ionosphere layer are observed and possible seismic events are tried to be determined. Vibrations caused by crustal movements in the earth cause not only concussion on humans but also some environmental changes that people cannot perceive directly. These changes can be modelled in such a way that different methods and devices can detect them. One of the main parameters in the examination of these methods is the change in Very Low Frequency (VLF) signal values. For this purpose, the changes in the lower ionosphere layer before and after the earthquake can be modelled with the changes obtained from VLF signals and the relationship between them can be used to determine the pre-earthquake ionospheric changes. The use of transient disturbances in this region of the ionosphere in VLF signals and remote sensing systems has been the subject of many studies. In the studies, it is seen that the VLF waves are based on the reflection rule of the ionosphere substrate (from the D region). It shows some observable changes on the electromagnetic waves that the ionosphere provides to be reflected within a few days before earthquakes. Understanding these changes with specific mathematical and statistical models reveals the possible precursors of earthquakes before they occur. In this study, January 17, 1995 Kobe (M = 7.2); January 6, 2008 (M=6.2) Greece Earthquake; April 25, 2015 (M=7.8) Nepal-Gorkha and the aftershocks of this earthquake on May 12, 2015 (M=7.3) Earthquake; January 12, 2010 (M=7.0) Haiti and 11-21 November 2016 Japan (M=6.1 and M=6.9) earthquakes in the lower ionosphere layer emitted as a result of the earthquake precursor results examination was carried out.
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