Low Frequency Radio Waves Research Articles

Auroral ecosystem services: A cascade model and investigation of co-production processes

This paper serves as an initial exploration of the stages involved in the formation of auroral ecosystem services (ES) and interactions between the geosphere, biosphere and anthroposphere. This is performed through the development of an auroral ES cascade model with the integration of four main co-production stages: (i) value attribution, (ii) mobilization of ES potential, (iii) value appropriation, and (iv) commercialization. The cascade model is expanded upon in detail by using examples from published academic and grey literature, highlighting the demand for capital inputs and strengthening the conceptual understanding of human-nature relationships in the context of auroral ES. The co-production stages illustrate the importance of action on the demand-side in order for the supply of benefits from auroral ES to be delivered. The potential for feedback from the anthroposphere into geophysical properties, processes and functions through anthropogenic space weather and artificial particle precipitation from the Van Allen Radiation Belts via ionospheric heating and low frequency radio wave generation is emphasized. Additionally, feedback via policy and decision making from the anthroposphere into the biosphere and geosphere is highlighted, especially in the context of managing light pollution and artificial space weather. The discussion considers the potential implications of the expanded model, in addition to the valuation of auroral ES across three value domains (monetary, socio-cultural and biophysical) and the potential use of such information in decision-making, followed by reflecting on the potential limitations of the expanded model.

Quantification of Lightning‐Induced Electron Precipitation Events on Electron Fluxes in the Radiation Belts

AbstractLightning‐induced Electron Precipitation (LEP) is a known process of electron loss in the Earth's radiation belts. An LEP event progresses with Very Low Frequency (VLF) radio wave radiation from lightning, trans‐ionospheric propagation, and wave‐particle gyroresonance interaction with energetic radiation belt electrons. Pitch angle scattered electrons then precipitate onto the ionosphere, allowing detection using VLF remote sensing using high power transmitters. The relative importance of LEP events as a radiation belt electron lifetime driver has heretofore been unclear. We build off a massive database of LEP events observed within the continental US (CONUS) by a network of VLF receivers. For each observed LEP event, based on the characteristics of the ionospheric disturbance, we apply a suite of models to estimate the total number of precipitating electrons, which we can then sum up over all LEP events to quantify lightning's contribution within CONUS. We find that LEP events within CONUS appear to be capable of removing a substantial fraction (up to 0.1%–1%) of radiation belt electrons between 33 and 1,000 keV, and may have stronger contributions to radiation belt losses than earlier estimates.

A D‐Region Ionospheric Imaging Method Using Sferic‐Based Tomography

AbstractWe present a tomographic imaging technique for the D‐region electron density using a set of spatially distributed very low frequency (VLF) remote sensing measurements. The D‐region ionosphere plays a critical role in many long‐range and over‐the‐horizon communication systems; however, it is unreachable by most direct measurement techniques such as balloons and satellites. Fortunately, the D region, combined with Earth's surface, forms what is known as the Earth‐Ionosphere waveguide allowing VLF and low frequency (LF) radio waves to propagate to global distances. By measuring these signals, we can estimate a path measurement of the electron density, which we assume to be a path‐averaged electron density profile of the D region. In this work, we use path‐averaged inferences from lightning‐generated radio atmospherics (sferics) with a tomographic inversion to produce 3D models of electron density over the Southeastern United States and the Gulf of Mexico. The model begins with two‐dimensional great circle path observations, each of which is parameterized so it includes vertical profile information. The tomography is then solved in two dimensions (latitude and longitude) at arbitrarily many altitude slices to construct the 3D electron density. We examine the model's performance in the synthetic case and determine that we have an expected percent error better than 10% within our area of interest. We apply our model to the 2017 “Great American Solar Eclipse” and find a clear relationship between sunlight percentage and electron density at different altitudes.

Impacts of Extreme Space Weather Events on September 6th, 2017 on Ionosphere and Primary Cosmic Rays

The strongest X-class solar flare (SF) event in 24th solar cycle, X9.3, occurred on 6 September 2017, accompanied by earthward-directed coronal mass ejections (CMEs). Such space weather episodes are known to cause various threats to human activities ranging from radio communication and navigation disturbances including wave blackout to producing geomagnetic storms of different intensities. In this study, SFs’ ionospheric impacts and effects of accompanied heliospheric disturbances on primary cosmic rays (CR) are investigated. This work offers the first detailed investigation of characteristics of these extreme events since they were inspected both from the perspective of their electromagnetic nature, through very low frequency (VLF) radio waves, and their corpuscular nature of CR by multi-instrumental approach. Aside data recorded by Belgrade VLF and CR stations, data from GOES and SOHO space probes were used for modeling and analysis. Conducted numerical simulations revealed a significant change of ionospheric parameters (sharpness and effective reflection height) and few orders of magnitude increase of electron density. We compared our findings with those existing in the literature regarding the ionospheric response and corresponding parameters. In addition, Forbush decrease (FD) magnitude, corrected for magnetospheric effect, derived from measurements, and one predicted from power exponents used to parametrize the shape of energetic proton fluence spectra at L1 were compared and found to be in good agreement. Presented findings could be useful for investigation of atmospheric plasma properties, particles’ modeling, and prediction of extreme weather impacts on human activities.

Statistics of Unusual Naturally Occurring VLF Radio Emissions Termed Bursty‐Patches Observed at Kannuslehto, Finland

AbstractWe report the results from a statistical study of a new type of naturally occurring, but differently structured very low frequency (VLF) radio waves called “VLF bursty‐patches.” Their main characteristic is that they are detected at frequencies above the electron gyrofrequency (fce) in the equatorial plane for the L‐shell of observation. Here we use the data from the station of Kannuslehto, Finland (KAN, MLAT = 64.4°N, L = 5.5) with fce ∼ 5–6 kHz where VLF bursty‐patches are commonly detected on at least 43% of its campaign days. We analyzed all available data for 2017 (∼8 months) separating the observations by spectral type, periodicity, number of bursts, observed frequency, and accompanying usual VLF emissions at lower frequencies (f < 6 kHz). We found that the overall highest occurrence rate is in the morning sector (05–12 MLT) correlating with general VLF occurrence rate at KAN (07–13 MLT, MLT = UT + 1.5 hr). Grouping usual VLF emissions and bursty‐patches showing similar spectral features, suggests that both groups are being generated by the same mechanisms (e.g., temperature anisotropy magnetospheric plasma distribution). However, unlike the situation for usual VLF emissions, the daily occurrence of bursty‐patches did not show a clear relationship with AE index. Superposed epoch analysis of magnetic components from the Sodankylä magnetometer (∼45 km from KAN) shows that VLF bursty‐patches are detected when the horizontal component of the magnetic field shows minimum variations. This suggests that propagation to the ground of bursty‐patches is conditioned to localized low variations of magnetic activity.

How to battle an army with vintage radio [broadcast special - radio

"The heroism and grit of our warriors leave no doubt that Ukraine will prevail," said the President of Ukraine, Volodymyr Zelensky, in a stirring speech broadcast on his government's YouTube channel. Ukraine is fighting two battles - one against a physical army and another against disinformation. One weapon in its arsenal that is helping it do both may be surprising: short-wave radio. This legacy technology is an old version of AM analogue radio that operates on low-frequency radio waves. It is used to transmit audio signals over long distances by bouncing them off layers of charged particles in the Earth's ionosphere, which is part of the upper atmosphere between 80 and 600km above sea level. Used by spies in the Cold War, short-wave radio is less complicated than newer communications options. It is still used in remote parts of the world where local broadcasting is not accessible, as well as in occupied and war-torn countries such as Ukraine. In these places, short-wave radio stations can provide a low-cost and effective lifeline to cut-off communities.

A New Method of Reconstructing Galactic 3D Structures Using Ultralong-wavelength Radio Observations

The free–free absorption of low-frequency radio waves by thermal electrons in the warm ionized medium of our Galaxy becomes very significant at ≲10 MHz (ultralong wavelength), and the absorption strength depends on the radio frequency. Upcoming space experiments such as the Discovering Sky at the Longest Wavelength and Farside Array for Radio Science Investigations of the Dark Ages and Exoplanets will produce high-resolution multifrequency sky maps at the ultralong wavelength, providing a new window to observe the universe. In this Paper we propose that from these ultralong-wavelength multifrequency maps, the 3D distribution of the Galactic electrons can be reconstructed. This novel and robust reconstruction of the Galactic electron distribution will be a key science case of those space missions. Ultralong-wavelength observations will be a powerful tool for studying the astrophysics relevant to the Galactic electron distribution, for example, the impacts of supernova explosions on electron distribution, and the interaction between interstellar atoms and ionizing photons escaped from the H ii regions around massive stars.

Estimation of the Fade Duration of Low-Frequency Radio Waves in the Earth–Ionosphere Waveguide under the Action of a Strong Local Perturbation in the Atmosphere

Estimation of the Fade Duration of Low-Frequency Radio Waves in the Earth–Ionosphere Waveguide under the Action of a Strong Local Perturbation in the Atmosphere

A Significant Sudden Ionospheric Disturbance Associated with Gamma-Ray Burst GRB 221009A

We report the detection of a significant sudden ionospheric disturbance in the D-region of Earth’s ionosphere (∼60–100 km), which was associated with the massive γ-ray burst GRB 221009A that occurred on 2022 October 9. We identified the disturbance over northern Europe—a result of the increased ionization by X- and γ-ray emission from the GRB-using very low frequency radio waves as a probe of the D-region. These observations demonstrate that an extra-galactic GRB (z ∼ 0.151) can have a significant impact on the terrestrial atmosphere and illustrates that the Earth’s ionosphere can be used as a giant X- and γ-ray detector. Indeed, these observations may provide an insight into the impacts of GRBs on the ionospheres of planets in our solar system and beyond.

Bayesian data analysis for sky-averaged 21-cm experiments in the presence of ionospheric effects

ABSTRACT The ionosphere introduces chromatic distortions on low frequency radio waves, and thus poses a hurdle for 21-cm cosmology. In this paper, we introduce time-varying chromatic ionospheric effects on simulated antenna temperature data of a global 21-cm data analysis pipeline, and try to detect the injected global signal. We demonstrate that given turbulent ionospheric conditions, more than 5 per cent error in our knowledge of the ionospheric parameters could lead to comparatively low evidence and high root-mean-square error (RMSE), suggesting a false or null detection. When using a constant antenna beam for cases that include data at different times, the significance of the detection lowers as the number of time samples increases. It is also shown that for observations that include data at different times, readjusting beam configurations according to the time-varying ionospheric conditions should greatly improve the significance of a detection, yielding higher evidences and lower RMSE, and that it is a necessary procedure for a successful detection when the ionospheric conditions are not ideal.

Investigations on Lanthanide polymers for radiation shielding purpose

The current study involves the X-ray/gamma and neutron/EMI shielding and change in mechanical properties of selected lanthanide polymers such as Lanthanum polymer, Cerium polymer, Praseodymium polymer, Gadolinium texaphyrin polymer, Terbium co-ordination polymer and Erbium phosphate hydrate polymer. The X-ray/gamma, neutron and EMI shielding parameters are studied in detail for all the selected polymers. Among all the selected polymers, Erbium phosphate hydrate polymer shows larger values of mass attenuation coefficient, absorption buildup factor, Zeff, Ne, specific absorbed fractions of energy, radiation protection efficiency, kinetic energy released in matter, relative dose, neutron total interaction cross section and absorption cross section values. Furthermore, the EMI shielding parameter (total shielding effectiveness) was also found to be larger for Erbium phosphate hydrate polymer in near infrared, mid infrared, far infrared, ultra high frequency (UHF), very high frequency, high frequency radio waves, middle frequency radio waves, low frequency radio waves and very low frequency radio waves. This clearly indicates that Erbium phosphate hydrate polymer might be used as a good shielding material for X-ray/gamma, neutrons and EMI radiations. We have also reported the change in mechanical properties of the studied lanthanide polymers due to the interaction with X-rays/gamma rays. The mechanical properties remains unchanged in the region where pair production and photoelectric effect dominates. Change in the mechanical properties is observed in the region where Compton scattering dominates, indicating that the change in mechanical properties due to interaction of radiation is also an important parameter while selecting the shielding materials. Present study may be useful in the selection of new shielding material.

Radiation shielding properties of Silicon boron alloys

The current study focuses on the shielding properties of selected Silicon-Boron alloys like of various compositions. Lower value of mass attenuation coefficient (MAC), half value thickness (HVL), tenth value thickness (TVL), penetration depth, electron density (Ne), effective atomic number (Zeff) and higher lead equivalent thickness, Radiation Protection Efficiency (RPE) and KERMA value which are essential characteristics of a good absorber for Si0.95B0.05. From these observations, it is clear that the silicon boron alloy Si0.95B0.05 is found to have larger value of mass attenuation coefficient, effective atomic number, radiation protection efficiency and KERMA, however, HVL, TVL and penetration found to be small. Furthermore, the EMI shielding parameter (total shielding effectiveness) was also found to be larger for the silicon boron alloy Si0.95B0.05 in near infrared, mid infrared, far infrared, ultra-high frequency (UHF), very high frequency, high frequency radio waves, middle frequency radio waves, low frequency radio waves and very low frequency radio waves. Neutron scattering lengths and cross-sections for the above alloys are also studied. This is identified as a good characteristic of X-ray/gamma absorber radiation, neutron shielding and EMI radiations. Thus, the Si-B alloy, Si0.95B0.05 may be used for X-ray/gamma radiation shielding.

Solar Flare Effects on the Earth’s Lower Ionosphere

Solar flares significantly impact the conditions of the Earth's ionosphere. In particular, the sudden increase in X-ray flux during a flare penetrates down to the lowest-lying D-region and dominates ionization at these altitudes (60-100 km). Measurements of very low frequency (VLF: 3-30kHz) radio waves that reflect at D-region altitudes provide a unique remote-sensing probe to investigate the D-region response to solar flare emissions. Here, using a combination of VLF amplitude measurements at 24kHz together with X-ray observations from the Geostationary Operational Environment Satellite (GOES) X-ray sensor, we present a large-scale statistical study of 334 solar flare events and their impacts on the D-region over the past solar cycle. Focusing on both GOES broadband X-ray channels, we investigate how the flare peak fluxes and position on the solar disk dictate an ionospheric response and extend this to investigate the characteristic time delay between incident X-ray flux and the D-region response. We show that the VLF amplitude linearly correlates with both the 1-8 A and 0.5-4 A channels, with correlation coefficients of 0.80 and 0.79, respectively. Unlike higher altitude ionospheric regions for which the location of the flare on the solar disk affects the ionospheric response, we find that the D-region response to solar flares does not depend on the flare location. By comparing the time delays between the peak X-ray fluxes in both GOES channels and VLF amplitudes, we find that there is an important difference between the D-region response and the X-ray spectral band. We also demonstrate for several flare events that show a negative time delay, the peak VLF amplitude matches with the impulsive 25-50 keV hard X-ray fluxes measured by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI).

A review of unusual VLF bursty-patches observed in Northern Finland for Earth, Planets and Space

Using numerical filtering techniques allowing us to reduce noise from sferics, we are able to clearly study a new type of differently structured very low frequency (VLF) radio waves above f = 4 kHz at the ground station of Kannuslehto in northern Finland (KAN, MLAT = 64.4°N, L = 5.5). These emissions are intriguing, since they are detected at frequencies above half the electron gyrofrequency in the equatorial plane (fce) for the L-shell of Kannuslehto (fce ~ 5–6 kHz). They are commonly observed at Kannuslehto, but have also been infrequently reported at other stations, sometimes under different names. Their possible common origin and manner of propagation is still under investigation. This paper unifies the nomenclature by regrouping all these waves detected at frequencies higher than the local equatorial 0.5 fce at the L-shell of observation under the name of VLF bursty-patches. While these waves have different spectral features, they appeared mostly composed of hiss bursts with durations of a few seconds to several minutes. They also show periodic features with varying periodicity and shape. They are sometimes characterized by single bursts covering very large frequency ranges of several kHz. We also give a review of the different characteristics of VLF bursty-patches observed at Kannuslehto, which at the moment, is the station with the highest observation rate. We present recent observations between 2019 and 2021.

Modulated Upper‐Hybrid Waves Coincident With Lower‐Hybrid Waves in the Cusp

AbstractDuring the Twin Rockets to Investigate Cusp Electrodynamics (TRICE‐2) High‐Flyer rocket's passage through the cusp the high frequency (HF) radio wave receiver observed three intervals of banded upper‐hybrid (UH) waves. The bands begin at the UH frequency (1.2–1.3 MHz), descending to as low as 1.1 MHz, with amplitudes of hundreds of mV/m. The spacing of the bands are 4.5–6 kHz and the number of bands ranges from 3 to 10. Simultaneously, the very low frequency (VLF) radio wave receiver observed lower‐hybrid (LH) waves with amplitudes ranging from 1 to 10 mV/m and frequencies of 4.5–6 kHz. Slight variations of the spacings of the bands in the UH waves were closely correlated with variations in the LH peak frequencies. Two possible wave‐wave interactions are explored to explain this phenomenon: decay of an UH wave into a lower frequency UH wave and a LH wave, and coalescence of independent UH waves and LH waves that spawn UH waves. Using a dispersion relation calculator with electron and ion distribution functions based off those observed by the particle instruments suggests that UH waves, and to a lesser degree LH waves, can be excited by linear instabilities. Kinematic analysis of the waves dispersion relations and the wave matching conditions show that wave‐wave interactions linking UH and LH modes are possible through either decay or coalescence. This analysis along with comparisons of the energy densities of the waves, and the ratio of their occupation numbers suggest that the decay process is more likely than coalescence.

IDENTIFIKASI PERSEBARAN AIR LINDI MENGGUNAKAN METODE VERY LOW FREQUENCY ELECTROMACNETIC (VLF-EM) DI TPA PUUWATU, KOTA KENDARI

Leachate which is a liquid released from waste due to biological degradation processes. If the leachate flow is allowed to flow to the surface of the soil, it will have negative effects on the surrounding environment. One of the geophysical methods that can be used to detect leachate distribution patterns is the VLF-EM (Very Low Frequency-Electromagnetic) method. The VLF-EM (Very Low Frequency-Electromagnetic) method is a geophysical method that utilizes electromagnetic principles using a low frequency radio wave source of 10-30 kHz. The research location is in TPA Puawatu, Kendari City. The analysis was carried out by looking at the 2D cross section of the flow density gained from the data processing. Qualitative interpretation can be carried out by the method developed by Karous-Hjelt with the producing of a 2-dimensional cross section with current density parameters. The high current density value can be identified as the most conductive anomaly. The direction of leachate distribution in the Puuwatu TPA tends to flow from the north of the TPA to the south of the TPA, which indicates that many swamps in the South of the TPA have been contaminated with leachate.

Spring‐Fall Asymmetry in VLF Amplitudes Recorded in the North Atlantic Region: The Fall‐Effect

AbstractA spring‐fall asymmetry is observed in daytime amplitude values of very low frequency (VLF) radio wave signals propagating over the North Atlantic during 2011–2019. We explore the processes behind this asymmetry by comparing against mesospheric mean temperatures and the semidiurnal solar tide (S2) in mesospheric winds. The solar radiation influence on VLF subionospheric propagation was removed from the daytime VLF amplitude values, isolating the fall‐effect. Similarly, the symmetric background level was removed from mesospheric mean temperatures undertaking comparable analysis. During fall, all three analyzed parameters experience significant deviation from their background levels. The VLF amplitude variation during spring is explained by the seasonal variation in solar illumination conditions, while the fall‐effect can be interpreted as a mean zonal wind reversal associated with both a S2 enhancement, and temperature reductions. Decreases in temperature can produce decreases in collision frequency, reducing VLF signal absorption, driving the observed VLF asymmetry.

Automated Large‐Scale Extraction of Whistlers Using Mask‐Scoring Regional Convolutional Neural Network

AbstractExtremely and very low frequency (ELF/VLF) radio waves are generated from a variety of natural geophysical sources. Ground‐based observations often contain signals of interest; however, the signals are typically immersed in a noisy environment due to lightning‐generated sferics and additional anthropogenic sources. Although automated detection algorithms have been employed successfully in the past, extraction of arbitrary and broadband signal classes has been a challenge. In this work, we employ a mask‐scoring regional convolutional neural network (MSRCNN) for automated extraction of whistlers from ground measurements at Palmer station, Antarctica. Statistics of several hundred thousand whistler receptions are evaluated to determine seasonal and diurnal variations at Palmer station along with strong correlations to lightning activity in the conjugate hemisphere. Although MSRCNN has been employed for whistler extraction in this work, the method has can be easily extended to other signal classes including chorus, hiss, and VLF triggered emissions.

Integration of Machine Learning Techniques in Virtual Wireless Sensor Network for insect monitoring

Agriculture industries are comparatively slow in adopting emerging technologies than any other industries despite lot of exciting research. The use of Wireless sensor network (WSN) is very important role in agriculture for more productive and sustainable growth. The structure of WSN is tightly application dependent. Every WSN have sensors, processing unit, low frequency radio wave transmitter and power supply using battery. With increasing number of interconnected WSN devices, there is substantial increase in data generation. It contains both control messages as well as application dependent data, collected by the sensors. The collected data are frequently sent to the nearest centralized controller for further processing and decision making. For continuous functioning of WSN, uninterrupted power supply is needed. Many researches are carried out to overcome these challenges. In this manuscript we are proposing a simple and effective machine learning techniques combined with pause and play method to increase battery life of WSN. This could be achieved in three stages play-pause-play (PPP) model. First by gathering data for some time (play mode), Second by putting WSN to sleep (pause mode), in the backend, apply machine learning algorithm that helps to build model from training data to predict the future data. At the final stage, put WSN back to play mode. Compare the result with actual data and fine tune the model to reduce the error. Using this method WSN will get enough sleep time to increase overall life by simulating the normal behaviour of sensor node. The sleep time will be calculated dynamically.

The Influence of Solar X-ray Flares on SAR Meteorology: The Determination of the Wet Component of the Tropospheric Phase Delay and Precipitable Water Vapor

In this work, we study the impact of high-energy radiation induced by solar X-ray flares on the determination of the temporal change in precipitable water vapor (ΔPWV) as estimated using the synthetic aperture radar (SAR) meteorology technique. As recent research shows, this radiation can significantly affect the ionospheric D-region and induces errors in the estimation of the total electron content (TEC) by the applied models. Consequently, these errors are reflected in the determination of the phase delay and in many different types of measurements and models, including calculations of meteorological parameters based on SAR observations. The goal of this study is to quantify the impact of solar X-ray flares on the estimation of ΔPWV and provide an estimate of errors induced if the vertical total electron content (VTEC) is obtained by single layer models (SLM) or multiple layer models (MLM) (these models do not include ionosphere properties below the altitude of 90 km as input parameters and cannot provide information about local disturbances in the D-region). The performed analysis is based on a known procedure for the determination of the D-region electron density (and, consequently, the vertical total electron content in the D-region (VTECD)) using ionospheric observations by very low frequency (VLF) radio waves. The main result indicates that if the D-region, perturbed by medium-sized and intense X-ray flares, is not modeled, errors occur in the determination of ΔPWV. This study emphasizes the need for improved MLMs for the estimation of the TEC, including observational data at D-region altitudes during medium-sized and intense X-ray flare events.