VLF Waves Research Articles

Complementary and Catalytic Roles of Man‐Made VLF Waves and Natural Plasma Waves in the Loss of Radiation Belt Electrons

AbstractBy simulating the energy and pitch angle diffusions of radiation belt electrons caused by ground‐based VLF transmitter waves, plasmaspheric hiss and lightning‐generated whistlers (LGWs), we quantitatively estimated the electron change rates caused by individual and multiple waves. We found that man‐made VLF waves and naturally generated hiss or LGWs play complementary and catalytic roles in the loss of radiation belt electrons. Man‐made VLF waves mainly reduce the hundreds of keV electrons in inner radiation belt (L < 2), but they alone cannot effectively remove the MeV electrons in slot region (L ∼ 2–3) because of unefficient diffusions at small pitch angles (<60°). On the contrary, natural hiss and LGWs do not affect the hundreds of keV electrons in the inner belt, but they are able to effectively reduce the hundreds of keV and MeV electrons at small pitch angles in the slot region. The loss of the small pitch electrons caused by hiss or LGWs offer a necessary phase space density gradient for the diffusion of large pitch angle MeV electrons (>60°) driven by man‐made VLF waves toward the loss cone. The combined diffusions by three types of the waves ultimately catalyze the loss of the large pitch angle MeV electrons in the slot region, and thus cause more electron losses in the wider energy and pitch angle ranges.

Using Principal Component Analysis to Characterize the Variability of VLF Wave Intensities Measured by a Low‐Altitude Spacecraft and Caused by Interplanetary Shocks

AbstractVery low frequency wave intensity measurements provided by the French low‐altitude DEMETER spacecraft are studied using the principal component analysis (PCA). We focus on both the physical interpretation of the first two principal components and their application to real physical problems. Variations of the first principal component (PC1) coefficients due to the geomagnetic activity and seasonal/longitudinal changes are studied. It is shown that their distribution corresponds to the wave intensity dependences obtained in previous studies. Moreover, the variations of PC1 coefficients around interplanetary shock arrivals are analyzed. The study is performed for fast forward (FF), fast reverse, slow forward, and slow reverse shocks separately. It shows that the most significant effect on the wave intensity is displayed in the FF case. Furthermore, it turns out that the wave intensity variations depend on the wave intensity detected before the shock arrival. Finally, the shock strength and interplanetary magnetic field orientation are also important. The performed analysis shows that PCA can be successfully applied to characterize large data sets of spacecraft measurements by limited sets of numbers—principal component coefficients (typically first one or two are enough), which still maintain a sufficient amount of information.

Storm-Time Features of the Ionospheric ELF/VLF Waves and Energetic Electron Fluxes Revealed by the China Seismo-Electromagnetic Satellite

This study reports the temporal and spatial distributions of the extremely/very low frequency (ELF/VLF) wave activities and the energetic electron fluxes in the ionosphere during an intense storm (geomagnetic activity index Dst of approximately −174 nT) that occurred on 26 August 2018, based on the observations by a set of detectors onboard the China Seismo-Electromagnetic Satellite (CSES). A good correlation of the ionospheric ELF/VLF wave activities with energetic electron precipitations during the various storm evolution phases was revealed. The strongest ELF/VLF emissions at a broad frequency band extending up to 20 kHz occurred from the near-end main phase to the early recovery phase of the storm, while the wave activities mainly appeared at the frequency range below 6 kHz during other phases. Variations in the precipitating fluxes were also spotted in correspondence with changing geomagnetic activity, with the max values primarily appearing outside of the plasmapause during active conditions. The energetic electrons at energies below 1.5 MeV got strong enhancements during the whole storm time on both the day and night side. Examinations of the half-orbit data showed that under the quiet condition, the CSES was able to depict the outer/inner radiation belt as well as the slot region well, whereas under disturbed conditions, such regions became less sharply defined. The regions poleward from geomagnetic latitudes over 50° were found to host the most robust electron precipitation regardless of the quiet or active conditions, and in the equatorward regions below 30°, flux enhancements were mainly observed during storm time and only occasionally in quiet time. The nightside ionosphere also showed remarkable temporal variability along with the storm evolution process but with relatively weaker wave activities and similar level of fluxes enhancement compared to the ones in the dayside ionosphere. The ELF/VLF whistler-mode waves recorded by the CSES mainly included structure-less VLF waves, structured VLF quasi-periodic emissions, and structure-less ELF hiss waves. A wave vector analysis showed that during storm time, these ELF/VLF whistler-mode waves obliquely propagated, mostly likely from the radiation belt toward the Earth direction. We suggest that energetic electrons in the high latitude ionosphere are most likely transported from the outer radiation belt as a consequence of their interactions with ELF/VLF waves.

Peculiarities of Heart Rate Variability Changes in Random-Bred Male Rats during Transition into Anesthetic Sleep under Stimulation of Central Neurotransmitter Systems.

General anesthesia with Nembutal (40 mg/kg) dramatically decreased the power of all waves of HRV spectrum in rats, especially in LF and VLF frequency bands, but the HR and respiration rate were little changed. At this, individual spectral peaks in HF range were observed at the same frequencies (1.3-1.5 Hz), which are characteristic of the wakeful state. Preliminary stimulation of noradrenergic system with maprotiline (10 mg/kg) increased the power of HF waves and elevated the respiratory rate in narcotized rats in comparison with the control values, although it did not shift the spectral peak at 1.5 Hz in frequency axis. Preliminary stimulation of cholinergic system with galantamine (2 mg/kg) somewhat decreased the power of HF waves and respiratory rate in narcotized rats (in comparison with the control values); additionally, it shifted HF peak to 1.1-1.4 Hz. Activation of serotonergic system with 5-hydroxytryptophan (50 mg/kg) and fluoxetine (3 mg/kg) decreased the HR, the power of HF waves, and respiratory rate in narcotized rats. It also shifted the spectral peak of HF waves to 0.9-0.95 Hz. Preliminary stimulation of dopaminergic system with L-DOPA (20 ml/kg) and amantadine (20 ml/kg) increased the power of VLF waves in narcotized rats in comparison with the control values. Numerous peaks appeared in HF (1.1-1.2 Hz) and VLF frequency bands. Generally, preliminary stimulation of serotonergic or dopaminergic systems markedly affects the neural activity under following general anesthesia: first aggravates the effect of anesthesia on vital centers in CNS, whereas second weakens the effect of anesthesia at the suprasegmental level of neural control.

Strong Amplification of ELF/VLF Signals in Space Using Neutral Gas Injections From a Satellite Rocket Engine

AbstractThe first demonstration of rocket exhaust driven amplification (REDA) of whistler mode waves occurred on May 26, 2020 by transferring energy from pickup ions in a rocket exhaust plume to EM waves. The source of coherent VLF waves was the Navy NML Transmitter at 25.2 kHz located in LaMoure, North Dakota. The topside ionosphere at 480 km altitude became an amplifying medium with a 60 s firing of the Cygnus BT‐4 engine. The rocket engine injected exhaust as a neutral cloud moving perpendicular to field lines that connected the NML transmitter to the VLF Radio Receiver Instrument (RRI) on e‐POP/SWARM‐E. Charge exchange between the ambient O+ ions and the hypersonic water molecules in the exhaust produced H2O+ ions in a ring‐beam velocity distribution. The 25.2 kHz VLF signal from NML was amplified by 30 dB for a period 77 s as observed by the RRI. Simultaneously, preexisting coherent ELF waves at 300 Hz were amplified by 50 dB during and after the Cygnus burn. Extremely strong coherent emissions and quasiperiodic bursts in the 300–310 Hz frequency range lasted for 200 s after the release. The excitation of an ELF whistler cavity may have lasted even longer, but the orbit of the SWARM‐E/e‐POP moved the RRI sensor away from the wave emission region. The amplified 300 Hz ELF waves may have gained even more energy by cyclotron resonance with radiation belt electrons as they were ducted between geomagnetic‐conjugate hemispheres.

ON THE POSSIBLE ORIG IN OF INTERNAL (2 3 HZ) MODULATION OF PULSATING AURORAS

Data of three all sky cameras in Kiruna and Tjautjas (Sweden) were used for estimation of altitude of pulsating arc like forms and investigation of so called internal modulation (2 3 Hz) during the ON phase of a few second pulsations. It is found that for two closely spaced arcs, internal modulation took place only in the lowest arc. Based on this finding , an explanation is proposed due to the pulsations of anomalous resistance in the field-aligned current associated with a pulsating structure appart to the traditional mechanism of particle scattering by VLF waves.

Ulcerative Lesions of the Mucosa Gastro-Duodenal Zone in Victims of the Chernobyl Accident: Some Features of the Etiology, Pathogenesis and Clinical Signs Identified in the Third of the Century After the Disaster

Ulcerative Lesions of the Mucosa Gastro-Duodenal Zone in Victims of the Chernobyl Accident: Some Features of the Etiology, Pathogenesis and Clinical Signs Identified in the Third of the Century After the Disaster

In situ Observations of Wave Transformation and Infragravity Bore Development Across Reef Flats of Varying Geomorphology

The character and energetics of infragravity (‘IG’, 25 s 250 s) waves over coral reef flats can enhance shoreline erosion or accretion, and also govern extreme shoreline events such as runup, overwash, and flooding on coral reef-lined coasts. Here we use in situ wave measurements collected along cross-reef transects at 7 sites on Pacific islands with varying reef geomorphologies to examine under what conditions IG waves occur and what factors enhance their irregularity. In general, a greater fraction of total wave energy was transferred to the IG band on reefs with steeper fore reef slopes and shallower reef flats. The IG wave amplitudes scaled with increasing water levels, but it was primarily at lower water levels when these waves became pitched onshore (negatively asymmetrical) and peaked (positively skewed). However, our results also highlight the importance of reef-flat width and slope as important morphological controls on IG waves, as the most asymmetric, bore-like, IG waves occurred on the wider reef flats, and the most skewed IG waves at the site with the steepest reef-flat. On the wider reef flats, IG wave-wave capture was observed during periods of large offshore wave forcing and enhanced VLF wave energy. Because similar IG wave motions over plane beaches enhance sea-swell (‘SS’, period < 25 s) bore-merging in the surf zone, we posit that VLF waves over reef flats may facilitate IG bore merging, and this may lead to larger, more pitched-onshore bores at the shoreline. In addition, greater IG wave heights appear to support the transmission of larger secondary short-period waves over the reef flat, independent of overall water levels. As irregular IG waves may be strong drivers of cross-reef sediment transport as well as runup, understanding the conditions and reef geomorphologies that lead to low-frequency, energetic bores on reef flats is critical to forecasting how coral reef-lined coasts will respond to sea-level rise and climate change.

Daytime VLF Emissions during the Magnetic Storm Recovery Phase: the Event of January 5, 2015

This paper discusses the spectral and temporal features of the 7-h daytime VLF noise emission burst in the frequency band of 1‒10 kHz observed on the Earth’s surface during the late recovery phase of a moderate magnetic storm (Kр = 5 and Dst ~ –80 nT) under nearly quiet space weather. These VLF emissions were recorded simultaneously at two auroral stations located at a geomagnetic latitude of ~64° MLAT and at a longitude distance of ~400 km from each other: Finnish Kannuslehto Station (KAN) and Russian Lovozero Observatory (LOZ). The dynamic VLF wave spectrum is considered at different time scales. During the development of the discussed daytime VLF burst, the noise emissions at below 3.5 kHz gradually turn into periodic (QP) emissions with a quasi-repetition of ~3 s. Having compared the directions of short isolated high-frequency (above 5 kHz) VLF signals (so-called “birds”) arriving at KAN and LOZ, we draw conclusions on the possible location and spatial dynamics of the exit area of emission from the ionosphere.

Effect of geomagnetic storms on VLF waves at low latitudes based on the analysis of whistlers and VLF emissions observed at Indian ground stations: A Review

Effect of geomagnetic storms on VLF waves at low latitudes based on the analysis of whistlers and VLF emissions observed at Indian ground stations: A Review

Evaluation of the possibility of wireless data transmission through rocks using an electromagnetic channel

The article provides an assessment of methods for solving the problem of implementing alarm systems in mines that are resistant to emergency situations, such as landslides and explosions, which can disable wired communication methods with personnel. To organize a signaling and emergency communication channel in mines for various purposes, the use of VLF and ULF (300 Hz - 30 kHz) electromagnetic waves is considered. A signal with an information message is received using an individual RFID tag informing personnel both in the conditions of stable operation of the mine and in emergency situations.

Simultaneous Observations of EMIC Waves, ELF/VLF Waves, and Energetic Particle Precipitation during Multiple Compressions of the Magnetosphere

Simultaneous observations of ELF/VLF and EMIC waves from Van Allen Probe satellites in the daytime Earth’s magnetosphere and on the ground during multiple compressions of the magnetosphere due to the fluctuations of the dynamic pressure of the solar wind are considered. Each magnetospheric compression leads to the generation of a wave burst in these frequency ranges. Based on data on the spectral and amplitude characteristics of the waves, measurements of the magnetic field, and the cold plasma density, the pitch-angle diffusion coefficients of protons and electrons in the vicinity of the loss cone are calculated. It is shown that ELF waves with frequencies of 30 keV) electrons; VLF waves at frequencies of 2–5 kHz may be responsible for precipitation of electrons with energy of ~1 keV. The EMIC waves observed from satellites and on the ground are related to the precipitation of protons with energies of 10–100 keV. The particle energies that correspond to the maxima of the diffusion coefficient are compared with the energies of the charged particles precipitating into the ionosphere, which were determined based on data from low-orbit POES satellites, and it is shown that they are in a good agreement with each other.

Bursts of Auroral-Hiss VLF Emissions on the Earth’s Surface at L ~ 5.5 and Geomagnetic Disturbances

We have studied the geomagnetic conditions during the occurrence of auroral-hiss VLF emissions on the Earth’s surface in the form of noise bursts at frequencies above 5–6 kHz. The study is based on an analysis of auroral-hiss observations at auroral latitudes in northern Finland at Kannuslehto station (KAN, L ~ 5.5) during the winter campaigns of 2013–2018. It is shown that auroral-hiss bursts are most often observed in the interval of 20–01 MLT under low geomagnetic activity (Kp < 3). It has been found that the bursts are typical for the growth phase of a magnetospheric substorm; the bursts cease abruptly at the onset of the substorm (the break-up of auroras), which is apparently due to a drastic increase in the absorption of VLF waves in the ionosphere. The bursts are often accompanied by the generation of geomagnetic Pi2 pulsations. VLF observations have shown that auroral-hiss bursts are not observed on the Earth’s surface in the main phase of magnetic storms; however, they are typical of the recovery phase. It has been found from model data that, during the occurrence of auroral hiss, KAN station is usually projected to the near-equatorial region of the auroral oval or to the zone of diffuse precipitation of more energetic electrons, i.e., to lower latitudes than the typical position of visible auroras during that time.

Study of VLF wave with relativistic effect in Saturn magnetosphere in the presence of parallel A.C. electric field

Cassini radio and plasma wave surveys aim to study radio emissions, plasma waves, thermal plasma and dust near Saturn. Using the characteristic solution and dynamics method, the influence of electron beam on the loss cone and bi-Maxwellian distribution of whistler mode waves in the parallel alternating electric field and magnetic field is studied. The dispersion relation and the growth rate of Saturn's magnetic layer were deduced and calculated in detail. Parameter analysis is performed by changing the parameters of the plasma like number density, AC frequency, temperature anisotropy, etc. The influence of AC frequency on Doppler shift and the comparative study of growth rate of oblique and parallel propagating waves are analyzed using generalized distribution function. We found temperature anisotropy AT=1.25 can explain the linear spatiotemporal growth rate of whistler mode waves. It provides the majority of the observed frequency integral power. It can be seen that the effective parameters for the generation of Whistler mode waves are not only temperature anisotropy, but also the relativistic factors discussed in the results and discussion section, and the AC field frequency and width of the loss cone distribution function.

Determination of the Ion Composition of the Outer Ionosphere from the Characteristics of ELF–VLF Waves Detected during the Operation of the Sura Facility

The propagation characteristics and physical nature of low-frequency waves observed in the ionosphere during heating of the near-Earth plasma by a powerful short-wavelength radiation are investigated using the singular value decomposition method. The experimental results obtained with the Sura midlatitude heating facility and detected by the onboard equipment of the DEMETER satellite were used. The ion composition of the near-Earth plasma is estimated from the spectral characteristics of the observed radio waves. The method is verified using results of full-scale measurements performed at altitudes corresponding to the Earth’s outer ionosphere.

On the ionospheric propagation of VLF waves generated by currents in the lower ionosphere

The consistent description of ELF/VLF wave propagation in the ionosphere is essential for understanding the properties of the wave phenomena observed both at the ground and satellites. Due to strong inhomogeneity of the lower ionosphere coupled with collisional damping of a wave, the geometrical optics approach is not valid, while the full-wave approach suffers from the problem of numerical instability. In this paper, we implement a rather general and powerful method avoiding the numerical instability to study propagation of the wave generated in the lower ionosphere. Our calculations demonstrate the quasi-periodic behaviour of the field in the upper ionosphere, which is associated with the Earth-ionosphere waveguide. The field distribution varies significantly with frequency, from being nearly sign-definite to oscillating with comparable positive and negative values, producing the ring structure in wave-vector space. The field distribution at the ground is studied and shown to have resonant structure defined by two parameters: number of the resonance, which depends on wave frequency, and spatial scale of the Earth-ionosphere waveguide.

Anomalous variations of VLF sub-ionospheric signal and Mesospheric Ozone prior to 2015 Gorkha Nepal Earthquake

The subject of pre-earthquake ionospheric signatures has always been contentious and debatable. Some of the previous reports have documented unforeseen and unusual variations in some of the atmospheric and ionospheric parameters well before an earthquake. Here, we analyze the ionospheric response from the Indian Subcontinent to Nepal Gorkha Earthquakes occurred between April and May 2015, which were the most powerful and disastrous natural calamities in past ~80 years over the Himalayan region left ~9000 causalities and more than ~20000 people injured with the property damage of the order of several billion dollars. In view of severe earthquakes occurrences, their prior information on the shorter time scales are warranted for mitigation of associated disasters. Here, we report for the first time, a case which shows a strong link in anomalous variations between VLF sub-ionospheric signal and mesospheric ozone prior to both April 25, 2015 (Mw = 7.8) earthquake and its biggest aftershock on May 12, 2015 (Mw = 7.3). Observations show an unusual variation in VLF signals amplitude /shift in terminator time (TT) strongly linked with positive (negative) mesospheric ozone anomaly in D-region altitudes prior to the Gorkha Nepal earthquakes. It is surmised that simultaneous continuous observations of both VLF waves and mesospheric ozone can be considered as an important tool to identify the prior earthquake signatures in the vicinity of the extremely earthquake-prone zone such as Himalayan region. In this context, the current report opens up a new dimension in lithosphere-atmosphere-ionosphere coupling during the earthquake preparation processes itself.

Localization of the sources of narrow-band noise VLF emissions in the range 4–10 kHz from simultaneous ground-based and Van Allen Probes satellite observations

This paper presents the results of simultaneous observations of narrow-band noise VLF emissions in the frequency range 4–10 kHz at Kannuslehto ground station in Northern Finland and by Van Allen Probes (previously RBSP) in the equatorial part of the magnetosphere. The event of December 25, 2015, is considered. During the event, narrow-band noise VLF emissions were detected on the Earth in two frequency ranges, f = 3.5–6 kHz and f = 8–10 kHz, between 1100 and 1300 UT. Narrow-band VLF emissions in the equatorial zone were also observed during that time by the RBSP-B satellite; their frequency was close to the electron equatorial half-gyrofrequency and gradually increased from 3 to 11 kHz during the satellite motion from L = 5.0 to L = 3.0. Analysis of the fine structure of the emissions on the ground showed that their spectral and temporal characteristics corresponded to emissions by the satellites in localized zones at different L-shells. The ground-based observations at lower frequencies correlated with the satellite observations at larger L-shells. In order to localize the regions of the generation of the VLF emissions observed at Kannuslehto auroral station at different frequencies, we calculated the ray trajectories of waves from the equator for the plasma density distributions detected by Van Allen Probes. The calculations of the trajectories showed that the VLF waves detected at Kannuslehto station could travel to the ground only if they propagated in the large-scale density ducts (700–900 km) observed by Van Allen Probes.

Enhancement and modulation of cosmic noise absorption in the afternoon sector at subauroral location (L = 5) during the recovery phase of 17 March 2015 geomagnetic storm

AbstractThe present study has focused on the intense production of cosmic noise absorption (CNA) at Maitri, Antarctica (L = 5; CGM −62°S, 55°E) during the early recovery phase of the largest storm of the current solar cycle commenced on 17 March 2015 St. Patrick's Day. The enhancement of CNA during 15–18 UT(14–17 magnetic local time (MLT); MLT = UT − 1 at Maitri) was as large as the CNA enhancement occurred during the main phase of the storm. During this time the CNA pattern also exhibits oscillation in the Pc5 (2–7 mHz) range and is in simultaneity with geomagnetic pulsations in the same frequency range. We observed the amplitude of CNA pulsation is well correlated with the level of CNA production. High‐amplitude Pc5 oscillations were observed in the vicinity of auroral oval near Maitri. Absence of electromagnetic ion cyclotron (EMIC) waves is marked suggesting the possible role of VLF waves in precipitation. The reason for the intense CNA production is found to be the precipitation caused mainly by hiss‐driven subrelativistic electrons. The CNA enhancement event is located well inside the dusk plasmaspheric bulge region as suggested by Tsurutani et al. (2015). Signature of enhanced eastward electrojet at Maitri during 14–17 MLT could be an additional factor for such large CNA. In order to establish the cause and effect relationship between the geomagnetic and CNA oscillations at Maitri, transfer entropy method has been used, which confirmed the modulation of CNA by geomagnetic pulsations.

Peculiarities of VLF wave propagation in the Earth's magnetosphere in the presence of artificial large‐scale inhomogeneity

AbstractWe study specific features of VLF waves propagation in the Earth's ionosphere and magnetosphere in the presence of large‐scale field‐aligned plasma inhomogeneities (ducts). These inhomogeneities can, e.g., be formed during the ionosphere heating by high‐power HF facilities such as High Frequency Active Auroral Research Program and “Sura.” They can extend up to altitudes of several thousand kilometers along geomagnetic field lines and have transverse scales of about 1° determined by the heated region scale. We analyze ray trajectories of VLF waves with frequencies of 1 to 15 kHz starting from about 100 km altitude and use the plasma parameters obtained within the framework of the SAMI2 simulation model (Huba et al., 2000). This model employs MHD equations for thermal plasma and allows one to obtain the plasma parameters along the entire magnetic flux tube in a fixed meridional plane. By knowing the ray trajectories, we calculate and compare the amplitude variation along the ray paths for the cases of unperturbed and heated ionosphere. We show that the presence of a large‐scale density disturbance produced by the HF heating can lead to significant changes of wave propagation trajectories. In particular, efficient guiding of VLF waves in this region can take place, which in turn can result in the appearance of several wave focusing regions and a drastic local increase of the VLF wave amplitude in these regions (up to ∼10 times as compared to the case of unperturbed plasma). The number of focusing regions is determined by an extension of an artificial duct along the geomagnetic field.