Radiation analysis of ground very low frequency sources

Solar flares, energetic particles, and Earth‐impacting coronal mass ejections enhance ionization in the lower ionosphere, inhibiting radio wave propagation in the Earth‐ionosphere waveguide (EIWG). This enhanced ionization is observed locally by ionosondes and GPS/GNSS receivers, but spatial coverage of these observations is limited by receiver location. Very low frequency (VLF) propagation studies have previously been performed to assess the impact of space weather on the EIWG; however, these studies are typically limited by small numbers of fixed VLF transmitters and receivers and observe only the region of the EIWG along propagation paths between transmitters and receivers. Here, we use global lightning as a VLF source and an existing lightning detection network as a receiver. By mapping sferic propagation paths between lightning strokes and numerous network stations and considering how this distribution of paths changes during solar events, we can identify attenuation regions in the EIWG caused by space weather. We describe the VLF response in the EIWG to two X‐class solar flares and compare mapped attenuation regions with those provided by the NOAA D‐Region Absorption Prediction model. The identified attenuation regions associated with these flares match the D‐Region Absorption Prediction‐predicted regions well in both spatial extent and onset timing. Measurements of VLF attenuation caused by solar flares can provide ground‐truth confirmation of modeled attenuation and can inform the detection efficiency of lightning location networks. This analysis also paves the way for real‐time VLF attenuation mapping in the EIWG.

A very low frequency (VLF) or extremely low frequency (ELF) dipole source has been created within the lower ionosphere by modulating the atmospheric dynamo currents with a ground-based high power HF source from the Arecibo Observatory. The authors and their colleagues have demonstrated that ELF or VLF generated in this way and injected into the earth-ionosphere waveguide could be received a few thousand kilometers away. The injection properties due to an array of ionospheric dipoles as a function of array geometry and element currents that will allow steerable ELF/VLF radiation within the earth-ionosphere waveguide are investigated theoretically. The ionospheric array factors for a linear and a planar array of Hertzian dipole sources are developed and their properties examined. The principle of pattern multiplication is then applied to include the effect of the ionospheric array element. This provides a means for predicting the field strengths at a remote receiving site due to a steerable linear or planar array of ionospheric sources generated by high power HF periodic plasma heating.

Very low frequency (VLF) propagation in the earth-ionosphere waveguide has been of interest for many decades. Most computational capabilities have been performed for a single frequency, with time-dependent results (such as those applied to lightning) obtained by inverse-Fourier-transforming these single-frequency components over a spectrum of frequencies. But if time-of-arrival (TOA) of a wave pulse is of interest, a less computationally-intensive method can be employed. Since a single spectral field component in the waveguide may be represented as a sum of modal fields, and since the group velocity is different for each mode, only the mode with the largest group velocity – the lowest order mode – need be calculated to obtain TOA information. This principle is demonstrated in detail for a simple waveguide, and applied to the earth-ionosphere waveguide.

A narrowband receiver was installed at the SANAE IV base in Antarctica to monitor specific very low frequency (VLF) radio signals from transmitters around the world. VLF waves propagating through the Earth–Ionosphere Waveguide are excellent probes of the varying properties of the lower region of the ionosphere. This paper describes the set-up of the narrowband system and demonstrates its capabilities with data from a set of solar flares on 08 February and 12 February 2010.

ABSTRACTA simplified model of a landing gear is tested in a wind tunnel to investigate the effect of the landing light location on the resulting noise generation. Examination of the near-field pressure fluctuations, combined with phase-locked stereoscopic particle imaging velocimetry of the unsteady wake identified two distinct sources of pressure fluctuations. The higher frequency source has a wide frequency band and is situated in the outer regions of the wake near the lights. On the other hand, the lower frequency source is found to be stronger, has a narrower frequency band and is developed further downstream in the wake, closer to the wake centreline. The lower frequency source is observed to be rather robust as it is hardly affected by the location of the landing lights, whereas the higher frequency source becomes weaker as the spacing between the lights is reduced. The effect of a splitter plate positioned downstream of the landing gear strut is also investigated as a means of reducing the lower frequency pressure fluctuations. Although the lower frequency source is considerably weakened by the splitter plate, substantial enhancement of the higher frequency source is observed.

In radiobiology we are interested in chemical effects of ionizing radiations only in so far as they may be involved in biological effects.2 As background for discussion of this relationship, let us briefly review the general state of our knowledge (or ignorance) of mechanisms of radiobiological actions: 1. The first event in such an action is, of course, the absorption of radiant energy by molecules in the biological object or its medium. The molecules which thus acquire energy in excess of normal are said to be activated. Some absorb so much energy that electrons are ejected; these molecules are said to be ionized. Others absorb less energy; electrons are merely shifted to other orbits; such molecules are said to be excited. The foregoing physical processes are at present fairly well understood, and many aspects of them can be described quantitatively. 2. After the absorption of energy, our knowledge of the radiobiological action is practically zero until the biological effect occurs. This effect—depending upon the biological object irradiated, the conditions of irradiation, the technic of observation, and a multitude of other factors—may be the mutation of a gene, the breaking of a chromosome, an increase in permeability of a membrane, an inhibition of cell division, a leukopenia, induction of a neoplasm, death of an animal, or any one of many other radiobiological phenomena. In all these diverse cases, however, there is no apparent resemblance between the biological effect and the initial physical phenomena associated with the absorption of energy. 3. From the foregoing considerations, it is evident that, during the so-called “latent period” which intervenes between the energy absorption and the observation of biological effect, a chain of important connecting events must occur. So far as I am aware, the specific nature of these events is in all cases unknown, as is also the number of successive events in the chain. However, in general it appears highly probable—and most physicists and radiobiologists have long considered it almost axiomatic—that at least the early events in the chain are chemical. Indeed, it is exceedingly difficult to imagine a mechanism of radiobiological action which does not involve chemical changes. The biological end-effects are changes in either physiology or morphology, these terms being used in the broad sense. The physiological changes clearly are changes in cell chemistry or are the results thereof. Moreover, when we recall that biological structures are built by chemical means, we can hardly imagine a morphological change which does not involve chemical change. Let us also consider the early part of the mechanism of radiobiological action. The high-energy radiations can ionize any type of molecule, and we may be confident that many kinds of molecules in the cell are thus highly activated under irradiation. Once a pair of ions is formed, they may do one of two things:

In this letter, Wait's exponential (EXP) model and international reference ionosphere (IRI) model are combined to study the diurnal variation characteristics of very low frequency (VLF) wave propagation. The EXP model is used below the IRI model to compensate for the subionosphere electron density lack of the IRI. The major EXP parameters are reconstructed from the lower IRI electron density for different times of the day. Being capable of characterizing the subionosphere details, the combined IRIEXP model gets higher accuracy than the pure IRI model for VLF diurnal variation prediction. The measurement result is replicated by using the finite-difference time-domain method to validate the presented model.

There are several sources of high energy radiations in the Universe. Each of them has a totally different emission mechanism. In this review, I concentrate on the study of the general properties of radiations emitted by matter which are accreted towards black holes and neutron stars. We also study the nature of X-ray radiation coming from the Sun in the form of energetic solar flares. These radiations are constantly bombarding the Earth’s ionosphere changing its electron content and affecting the wave propagation through the Earth and the lower-ionosphere waveguide. We monitor Very Low Frequency (VLF) radio waves and correlate our observations with the presence or absence of the high energy radiations from space. Our results during solar flares, show how the number density of the ionosphere is enhanced by these celestial sources. The terrestrial high energy phenomena such as earthquakes are believed to affect the ionospheric properties and we have monitored VLF signals during earthquakes and found possible effects of seismic events on the VLF signals.

Satellite launch vehicle effect on the Earth’s lower ionosphere: A case study

Artificial ionospheric disturbances are created by intense high-frequency (HF) radiation from ground-based facilities and very-low-frequency (VLF) radiation from Navy transmitters. We apply Stanford Full-Wave Method (SFWM) to scattering of the VLF waves propagating in the Earth-ionosphere waveguide (EIW) by such ionospheric disturbances, using Born approximation. The waves are scattered both into the EIW (in the forward direction) and into the ionosphere (both forward and upward into a whistler “column”). In the case of HF heating, the upward-scattered wave intensity may significantly exceed the waveguide leakage into the ionosphere, while for the VLF-heated ionosphere, it is relatively small.

Today, the HV withstand testing with DC or AC voltage of industrial frequency is required for all newly constructed or repaired cable lines. DC Testing of XPLE insulated cables inevitably shortened the length of service of a cable due to the formation of volume charge in the water-filled microcavities. On the other hand, the test equipment used AC voltage source of industrial frequency is expensive and difficult to operate in the field due to high capacitance of a cable line. To solve this problem, we suggest using very low frequency (VLF) test on 0.1 Hz. The advantages and disadvantages of VLF testing are compared. Additional parameters that characterize not only the performance, but also the residual life of the cable can be obtained with VLF tests are studied. These include measuring of partial discharge intensity and loss factor tan δ.

Synoptic and mesoscale cyclonic systems over the ocean and seas are often accompanied by thunderstorm activity, the intensity and spatial distribution of which is modulated by the dynamic structure of these systems. Lightning discharges are sources of electromagnetic radiation in the range of very low frequencies (VLF) and are detected by VLF location finders. Using the World Wide Lightning Location Network (WWLLN), relations between characteristics of fields of detected lightning discharges in the north-western part of the Pacific Ocean and those of fields of meteorological elements of weather formations estimated by data of remote sensing of the Earth by satellites are studied by an example of tropical cyclones. We illustrate a technique permitting one to connect thunderstorm activity parameters (frequency and intensity, as well as spatial distribution of lightning discharges) with the structure of weather systems over oceans and seas and with the intensity and forms of mesoscale formations distinguished in these systems by fields of the near-water wind vortex (the fields are obtained using a scatterometer) and by satellite images in the visible and infrared ranges. The relations between the frequency and density of lightning discharges in the range of influence of a tropical cyclone (TC) and spatial distribution of the near-water wind vortex are demonstrated by an example of individual TCs of 2005–2013.

Enhanced solar radiation absorption by carbon dioxide in thermodynamic nonequilibrium: A computational study

Electromagnetic energy is the backbone of wireless communication systems, and its progressive use is considered to have a low but measurable impact on a wide range of biological systems. Even though a growing amount of data has reported electromagnetic energy absorption in humans along with subsequent biological effects, the consequences of electromagnetic energy absorption on plants have been insufficiently addressed. The higher surface to volume ratio along with the enormous water-ion concentrations makes the plant an ideal model to interact with non-ionizing electromagnetic radiation. In this study, controlled and periodic electromagnetic exposure of 1837.50 MHz, 2.75 W/m2 for 6 h a day on a popular rice variety (var. Satabdi) reduced the seed germination rate. The same dose of periodic electromagnetic exposure upregulated phytochrome B and phytochrome C gene transcripts in 12-day-old seedlings, whereas, in 32-day-old plants, the dose upregulated calmodulin and phytochrome C while the bZIP1 gene showed repression. However, the transcript abundance of bZIP1, phytochrome B, and phytochrome C genes was enhanced even in 12-day-old Satabdi seedlings following instantaneous short-duration (2 h 30 min) controlled electromagnetic exposure to 1837.50 MHz, 2.75 W/m2 . The reported responses in rice were observed below the international electromagnetic regulatory limits. Thus, rice plants perceived electromagnetic energy emitted by the wireless communication system as abiotic stress as per its response by upregulation or repression of known stress-sensing genes. Bioelectromagnetics. © 2020 Bioelectromagnetics Society.

A very bright fireball observed over New South Wales in 1978 produced anomalous sounds clearly audible to some of the observers. An investigation of the phenomenon indicates that bright fireballs radiate considerable electromagnetic energy in the very-low-frequency (VLF) region of the spectrum. A mechanism for the production of VLF emissions from the highly energetic wake turbulence of the fireball is proposed. Trials with human subjects revealed a very extended range of thresholds for the perception of electrically excited sounds among a sample population, particularly when the VLF electric field excites surface acoustic waves in surrounding objects. This fact, together with variable propagation effects and local conditions, can account for the sporadic distribution of reports of anomalous sounds from fireballs and auroras.