Very Low Frequency Research Articles

High-Altitude Discharges and Whistlers of Volcanic Thunderstorms

The results of the observations of atmospherics and whistlers initiated by high-altitude electrical discharges that occurred during the eruption of the Kamchatka volcanoes (Bezymianny and Shiveluch (Russia)) on 7 and 10 April 2023 are presented. Recording of atmospherics and associated whistlers was carried out by a VLF (very low frequencies) radio direction finder. Two-hop whistlers were identified by dispersion coefficient, which corresponded to the double passage of the signal from Kamchatka to Australia and back. The heights of the electric discharges were determined by means of interferograms of direct and reflected from the ionosphere radiofrequency atmospherics. The high-altitude distribution of an electric discharge is obtained, the penetration of which into the ionosphere is responsible for the generation of whistlers. The characteristics of volcanic electrical discharges and whistlers can be used to estimate the height of an explosive eruption.

Correlation Study on the Autonomic Nervous System Balance Using HRV According to Preference for Spicy Taste

Objectives: People generally seek out spicy taste when stressed. Eating spicy food activates the autonomic nervous system, causing the body to sweat and the heart to beat faster. The objective of the study is to investigate the correlation with the autonomic nervous system balance according to the preference for spicy taste using HRV.Method: This study measured the changes in heart rate using SA-3000P in patients who visited the local clinic between January and May 2023. To minimize any fluctuations in the autonomic nervous system before measurement due to external factors, subjects were asked to sit in a chair or lie down to rest for approximately 10 minutes before the test and any jewelry were asked to be removed. The test involved attaching ECG electrodes on both wrists and left ankle to measure the autonomic nervous system indicators by measuring, detecting and recording data for 5 minutes. For HRV measurements, SDNN (standard deviation of all normal R-R intervals) was obtained using time domain analysis, and TP (total power), VLF (very low frequency, 0.003∼0.04 Hz), LF (low frequency, 0.04∼0.15 Hz), HF (high frequency, 0.15∼0.4 Hz), and LF/HF ratio were calculated using frequency domain analysis. Additionally, using the measurements, indicators such as RMSSD (root mean square of the successive difference), autonomic nerve activation, and fatigue were produced.Results: The group that preferred spicy taste showed significantly lower TP, LF, HF, RMSSD, and autonomic nerve activation compared to the control group; VLF was lower but there was no statistically significant difference. Fatigue was higher in the group that preferred spicy taste compared to the control group with statistical significance; LF/HF Ratio was higher but with no statistically significant difference.Conclusion: The preference for spicy taste may cause autonomic nervous system abnormality; thus, it may be advisable to avoid the intake of spicy foods.

Pretreatment Cranial Computed Tomography Perfusion Predicts Dynamic Cerebral Autoregulation Changes in Acute Hemispheric Stroke Patients Having Undergone Recanalizing Therapy: A Retrospective Study

Objectives: Blood pressure (BP) management is challenging in patients with acute ischemic supratentorial stroke undergoing recanalization therapy due to the lack of established guidelines. Assessing dynamic cerebral autoregulation (dCA) may address this need, as it is a bedside technique that evaluates the transfer function phase in the very low-frequency (VLF) range (0.02–0.07 Hz) between BP and cerebral blood flow velocity (CBFV) in the middle cerebral artery. This phase is a prognostically relevant parameter, with lower values associated with poorer outcomes. This study aimed to evaluate whether early cranial computed tomography perfusion (CTP) can predict this parameter. Methods: In this retrospective study, 165 consecutive patients with hemispheric strokes who underwent recanalizing therapy were included (median age: 73 years; interquartile range (IQR) 60–80; women: 43 (26%)). The cohort comprised 91 patients treated with intravenous thrombolysis (IV-lysis) alone (median National Institute of Health Stroke Scale (NIHSS) score: 5; IQR 3–7) and 74 patients treated with mechanical thrombectomy (median NIHSS: 15; IQR 9–18). Regression analysis was performed to assess the relationship between pretreatment CTP-derived ischemic penumbra and core stroke volumes and the dCA VLF phase, as well as CBFV assessed within the first 72 h post-stroke event. Results: Pretreatment penumbra volume was a significant predictor of the VLF phase (adjusted r2 = 0.040; β = −0.001, 95% confidence interval (CI): −0.0018 to −0.0002, p = 0.02). Core infarct volume was a stronger predictor of CBFV (adjusted r2 = 0.082; β = 0.205, 95% CI: 0.0968–0.3198; p = 0.0003) compared to penumbra volume (p = 0.01). Additionally, in the low-frequency range (0.07–0.20 Hz), CBFV and BP were inversely related to the gain, an index of vascular tone. Conclusion: CTP metrics appear to correlate with the outcome-relevant VLF phase and reactive hyperemic CBFV, which interact with BP to influence vascular tone and gain. These aspects of dCA could potentially guide BP management in patients with acute stroke undergoing recanalization therapy. However, further validation is required.

Deep Learning Model Size Performance Evaluation for Lightning Whistler Detection on Arase Satellite Dataset

The plasmasphere within Earth’s magnetosphere plays a crucial role in space physics, with its electron density distribution being pivotal and strongly influenced by solar activity. Very Low Frequency (VLF) waves, including whistlers, provide valuable insights into this distribution, making the study of their propagation through the plasmasphere essential for predicting space weather impacts on various technologies. In this study, we evaluate the performance of different deep learning model sizes for lightning whistler detection using the YOLO (You Only Look Once) architecture. To achieve this, we transformed the entirety of raw data from the Arase (ERG) Satellite for August 2017 into 2736 images, which were then used to train the models. Our approach involves exposing the models to spectrogram diagrams—visual representations of the frequency content of signals—derived from the Arase Satellite’s WFC (WaveForm Capture) subsystem, with a focus on analyzing whistler-mode plasma waves. We experimented with various model sizes, adjusting epochs, and conducted performance analysis using a partial set of labeled data. The testing phase confirmed the effectiveness of the models, with YOLOv5n emerging as the optimal choice due to its compact size (3.7 MB) and impressive detection speed, making it suitable for resource-constrained applications. Despite challenges such as image quality and the detection of smaller whistlers, YOLOv5n demonstrated commendable accuracy in identifying scenarios with simple shapes, thereby contributing to a deeper understanding of whistlers’ impact on Earth’s magnetosphere and fulfilling the core objectives of this study.

Ultra-relativistic electron flux enhancement under persistent high speed solar wind stream

The physical mechanisms usually applied to explain the relativistic electron enhancement have been delved into to elucidate non-adiabatic electron acceleration resulting in the ultra-relativistic electron population observed in the outer radiation belt. We considered multisatellite observations of the solar wind parameters, magnetospheric waves, and particle flux to report an unusual local acceleration of ultra-relativistic electrons under a prolonged high-speed solar wind stream (HSS). A corotating interaction region reaches the Earth’s bowshock on August 3, 2016, causing a minor geomagnetic storm. Following this, the magnetosphere was driven for 72 h by a long-term HSS propagating at 600 km/s. During this period, the magnetosphere sustained both ultra-low frequency (ULF) and very-low frequency (VLF) waves in the outer radiation belt region. Besides the waves, the relativistic and ultra-relativistic electron fluxes were enhanced with different time lags regarding the magnetic storm main phase. The efficiency of wave-particle interaction in enhancing ultrarelativistic electrons is evaluated by the diffusion coefficient rates, considering both ULF and VLF waves together with phase space density analyses. Results show that local acceleration by whistler mode chorus waves can occur in a time scale of 2–4 h, whereas ULF waves take around 10’s of hours and magnetosonic waves take a time scale of days. This result is confirmed by the phase space density analysis. Accordingly, it shows that peaks of local acceleration of 1 MeV electrons are consistent with the observation of the highest chorus wave amplitude at the same L-shell and MLT. Thus, we argue that whistler mode chorus waves interacting with relativistic electrons are the main physical mechanisms leading to ultra-relativistic electron enhancement, while ULF and fast magnetosonic waves are found as secondary physical processes. Lastly, our analysis contributes to understanding how whistler and ULF waves can contribute to ultra-relativistic electrons showing up in the inner magnetosphere under the HSS driver.

Effects of urination process on heart rate variability.

Heart rate variability (HRV) is used for the assessment of activity of the autonomic nervous system (ANS). As urination is also under the control of the ANS, this study aimed to investigate the usefulness of HRV in the assessment of ANS during the peri-urination period. The psychological effects of sitting on a chair or on the toilet during pre- and post-urination periods were also assessed. Electrocardiogram was used to measure HRV in male participants (n = 40, aged 18-30). They were allowed to drink water to ease urination. At the stage close to voiding, six measurements (each for 90s) were taken sequentially in sitting position (pre-urination chair, pre-urination toilet, urination, post-urination toilet, post-urination chair, and basal post-urination chair). HRV indices included standard deviation of R-R intervals (SDNN), root mean square of successive differences in R-R intervals (RMSSD), percentage of successive R-R intervals differing more than 50ms (pNN50), total power (TP), very-low-frequency (VLF), low-frequency (LF), and high-frequency (HF) bands together with the ratio of LF/HF. HR, SDNN, TP, LF, and LF/HF increased during urination process (P < 0.05), whereas RMSSD, pNN50, and HF increased before urination on toilet (P < 0.05) compared to sitting on a chair before and after urination. HRV indices dynamically reflected the physiological stages of urination. Parasympathetic activity (revealed by pNN50, RMSSD, and HF) increased before urination, whereas sympathovagal balance (revealed by LF/HF) increased during urination. Thus, HRV appears to be a suitable technique for studying physiological and pathological aspects of urination.

Characterization of gravity wave events detected in the low ionosphere at the Brazilian Antarctic Station

Here we present the characteristics of three distinct types of Gravity Wave (GW) events as detected in the low ionosphere using very low frequencies (VLF) radio measurements performed at the EACF, Brazilian Antarctic Station Comandante Ferraz (62° 5′ 6″ S, 58° 24′ 12″ W), on King George Island. GWs in the low ionosphere produce oscillations in the electron density, which can be detected as amplitude and phase fluctuations of the VLF signals. The properties of the GW events are obtained using Morlet's Wavelet analysis, which gives the period of the waves, and their occurrence time. The period and duration of the GW events obtained using the VLF technique presented good agreement with ones previously obtained from airglow observations from a co-located all-sky imager. The VLF detection of the mesospheric front showed the same morphology seen with the imager with four crests identified, and the wave activity presented similar period range (∼4–16 min) as observed by airglow (∼6 min) with a period peak of 14 min equal to the spectral analysis of the concurrent OH temperature data. The activity associated with the band event presented similar period of ∼10 min (imager observed 13 min), same duration of 4 h as well as peak intensity just before 05:00 UT. The ripple detection showed the same period of 8 min as the airglow observations and similar duration of around 25 min. By considering two distinct VLF paths it was also possible to analyze the direction and velocity of propagation for the mesospheric front event, which gives 96.0 (±4.8) ms−1 in the East direction in agreement with the velocity of ∼92 ms−1 in the Northeast direction obtained from the airglow observations.

Assessment of Cardiac Autonomic Function by Short-Term Sensor-Based and Long-Term Heart Rate Variability Analyses in Individuals with Spinal Cord Injury After Long-Term Table Tennis Training.

This study aimed to examine the acute and chronic effects of an exercising table tennis program on cardiac Autonomic Nervous System (ANS) and functional capacity in people with tetraplegia. Twenty males with tetraplegia (C6-C7), with a mean age of 38.50 ± 4.04 years old, were randomly assigned into two equal groups: A, who followed a 6-month exercise training program with table tennis 3 times per week, and B, who remained untrained. Additionally, 11 healthy sedentary men (group C) with a mean age of 39.71 ± 5.87 years old participated in the study as healthy controls. At baseline, all participants underwent a short-term (5 min) and a long-term (24 h ambulatory) ECG monitoring to evaluate the heart rate variability (HRV) indices and a maximal arm ergometric and dynamometric testing of the upper limbs. Moreover, the acute cardiac autonomic responses to maximal arm cycle exercise test were evaluated by Polar S810i sensor chest strap. At the end of the 6-month study, all parameters were revaluated only in groups A and B. At baseline, there was no statistically significant difference between the two patient groups. However, intra-group changes at the end of the 6-month study regarding the 24-h HRV monitoring indicated that group A statistically increased the standard deviation of R-R intervals (SDNN) by 13.9% (p = 0.007), the standard deviation of R-R intervals calculated every 5 min (SDANN) by 8.4% (p = 0.007), the very low frequency (VLF) by 7.1% (p = 0.042), and the low frequency [LF (ms2)] by 10.5% (p = 0.009), which almost reached the levels of group C. Favorable improvements were also noticed at the end of the study for group A in maximal exercise time of the upper limbs by 80.4% (p < 0.001) and maximal strength of the right hand by 27.8% (p < 0.001). Linear regression analysis after training showed that maximal exercise time was positively correlated with SDNN (r = 0.663, p = 0.036) and with LF (ms2) (r = 0.623, p = 0.045). Our results indicate that a 6-month table tennis training program is efficient and can improve cardiac ANS activity mainly by increasing sympathovagal balance.

Implication of heart rhythm complexity in predicting long-term outcomes in pulmonary hypertension

Pulmonary hypertension (PH) is a serious disease, however simple tools to predict outcomes are lacking. In our previous investigation, we found that heart rate variability (HRV) and heart rhythm complexity (HRC) were associated with the detection and severity of PH, however their association with PH mortality remains unclear.The aim of this study was to investigate these metrics as a tool for determining long-term outcomes in PH patients. We enrolled 74 Asian PH patients with WHO PH group 1 or 4 at a single hospital in Taiwan between March 2012 and June 2018. After a median follow-up duration of 58 months (to January 2023), 22 patients had died. The patients who died had a significantly lower lean body mass index (BMI), impaired renal function, higher N-terminal pro B-type natriuretic peptide (NT-proBNP) level, lower very low-frequency (VLF), lower short-term detrended fluctuation analysis α1 (DFAα1), and lower multiscale entropy scale 5 value. In multivariable analysis, BMI, VLF and multiscale entropy scale 5 were significantly associated with survival. The best cut-off VLF and scale 5 values were 115.13 and 0.738, respectively. We then categorized the study population into three groups: both elevated VLF/scale 5 (group 1), either depressed VLF or depressed scale 5 (group 2), and both depressed VLF/scale 5 (group 3). The results showed that group 1 had the best outcomes, whereas group 3 had the worst survival (P < 0.001).Combining HRV and HRC metrics appears to be a good non-invasive tool to predict the long-term outcomes of patients with PH.

Effect of transcutaneous electrical acupoint stimulation at different frequencies on mild hypertension: A randomized controlled trial

BackgroundTranscutaneous electrical acupoint stimulation (TEAS) may contribute to blood pressure (BP) control, but the evidence remains insufficient. Our objectives were to evaluate the impact of TEAS on hypertension and determine the optimal frequency. MethodsA total of 120 hypertensive patients were randomly allocated to the TEAS-2Hz group, TEAS-10Hz group, or usual care control group in a 1:1:1 ratio. All patients were advised to continue their usual antihypertensive regimen. Additionally, patients in the TEAS groups received TEAS therapy 3 times per week for 4 weeks, with a 4-week follow-up. ResultsThe primary outcome was the change in systolic BP (SBP) from baseline to week 4. Secondary outcomes included changes in diastolic BP (DBP), mean arterial pressure (MAP), heart rate (HR), heart rate variability (HRV), and 12-item health survey (SF-12) at different time points. Both TEAS groups showed reductions in SBP relative to control (TEAS-2Hz group vs. control, −4.70 mmHg [95 % CI, −7.00 to −2.40 mmHg]; P < 0.001; TEAS-10Hz group vs. control, −8.66 mmHg [95 % CI, −10.97 to −6.36 mmHg]; P < 0.001). TEAS-10Hz provided a significant decrease in SBP than TEAS-2Hz (-3.96 mmHg [95 % CI, −1.66 to −6.26 mmHg]; P< 0.001). TEAS groups also exhibited reductions in DBP, MAP, HR, LF/HF ratio（LF/HF）, very low frequency (VLF), and normalized low frequency (LF norm), and an increase in normalized high frequency (HF norm) than control. No differences were observed among groups in low frequency (LF), high frequency (HF), total power (TP), very low frequency (VLF), and SF-12. ConclusionTEAS might be a promising adjunctive therapy for hypertension, and the recommended frequency is 10 Hz, which should be confirmed in larger trials.

High sensitivity measurement of ULF, VLF, and LF fields with a Rydberg-atom sensor.

Fields with frequencies below megahertz are challenging for Rydberg-atom-based measurements, due to the low-frequency electric field screening effect caused by the alkali-metal atoms adsorbed on the inner surface of the container. In this paper, we investigate electric field measurements in the ultralow frequency (ULF), very low frequency (VLF), and low frequency (LF) bands in a Cs vapor cell with built-in parallel electrodes. With optimization of the applied DC field, we achieve high-sensitive detection of the electric field at frequencies of 1 kHz, 10 kHz, and 100 kHz based on the Rydberg-atom sensor, with the minimum electric field strength down to 18.0 μV/cm, 6.9 μV/cm, and 3.0 μV/cm, respectively. The corresponding sensitivity is 5.7 μV/cm/Hz1/2, 2.2 μV/cm/Hz1/2, and 0.95 μV/cm/Hz1/2 for the ULF, VLF, and LF fields, which is better than a 1-cm dipole antenna. Besides, the linear dynamic range of the Rydberg-atom sensor is over 50 dB. This work presents the potential to enable more applications that utilize atomic sensing technology in the ULF, VLF, and LF fields.

Automatic Extraction of VLF Constant‐Frequency Electromagnetic Wave Frequency Based on an Improved Vgg16‐Unet

AbstractConstant Frequency Electromagnetic Waves (CFEWs) refer to electromagnetic waves with a constant frequency. Man‐made CFEWs are mainly used in wireless communication, scientific research, global navigation and positioning systems, and military radar. CFEWs exhibit horizontal line characteristics higher than the background on spectrograms. In this study, we focus on Very Low Frequency (VLF) waveform data and power spectral data collected by the China Seismo‐Electromagnetic Satellite (CSES) Electromagnetic Field Detector (EFD). We utilize deep learning techniques to construct an improved Vgg16‐Unet model for automatically detecting horizontal lines on time‐frequency spectrogram and extracting their frequencies. First, we transform waveform data into time‐frequency spectrogram with a duration of 2 s using Short‐Time Fourier Transform. Then, we manually label horizontal lines on the time‐frequency spectrogram using the Labelme tool to establish the dataset. Next, we establish and improve the Vgg16‐Unet deep learning model. Finally, we train and test the model using the dataset. Statistical experimental results show that the error rate of line detection is 0, indicating high reliability of the model, with fewer parameters and fast computation speed suitable for practical applications. Not only do we detect lines through the model, but we also obtain their frequencies. Additionally, in batch‐generated power spectrogram of CFEWs, we discover some unstable phenomena such as frequency shifts and fluctuations, which contribute to understanding the propagation mechanism of CFEWs in the ionosphere and improving the accuracy of related systems.

A Machine to Listen to the Sky: Transducing Space Weather

A Machine to Listen to the Sky: Transducing Space Weather delves into the intersection of art, science, and technology by capturing electromagnetic signals from natural and man-made sources. Using custom-built Very Low Frequency (VLF) antennas, Tapper explores the invisible soundscape created by space weather and terrestrial activity, including solar radiation lightning, and power grids. His work investigates how these signals interact with the Earth’s ionosphere, transforming scientific phenomena into artworks disseminated through workshops, installations, and field recordings.

Modeling of the Variability of D‐Region Ionospheric Electron Density During Solar Cycle‐24

AbstractSolar cycle variation of earth's atmosphere, particularly the ionosphere is of particular interest in the field of space science and space weather studies. In this article, we present the outcome of our detailed quantitative study on solar cycle variation of lower ionospheric properties using numerical investigation. First, we seek to model and compare the collective D‐region ionization rates (’s) due to the individual contributions from the ionizing sources, namely, (a) solar extreme ultraviolet (EUV) radiation including the Lyman‐ irradiation and (b) solar X‐ray irradiation throughout the solar cycle (C24). Then, we compute the electron density profiles using the ionization rates. We report significant solar cycle variation in ionization rate and electron density profiles for the entire span of C24. We use the sunspot number (SPN) profile to substantiate the finer details of profile during C24. For the segments of the D‐region above two different geographic coordinates, we report that profiles show a consistent “dual peak” nature. It is very similar to the SPN profile during C24. As a next‐order validation, we compare our modeled profiles with their IRI‐2020 counterpart (s). Their overall trends are found to be in agreement. Finally, we discuss the response of the D‐region in terms of due to C24. The work lays the foundation for our upcoming studies on D‐region response to solar cycle variation with Very Low Frequency (VLF) observation.

Influence of autonomic nervous dysfunction on eating during hemodialysis sessions: An observational study.

Although some studies have indicated that eating during hemodialysis may induce hypotension and cardiovascular events, some patients still consume food during their treatment. This prospective study was conducted to determine whether the need to eat during hemodialysis treatment was related to abnormal glucose metabolism and autonomic nerve dysfunction. Seventy patients were enrolled in this study, and their demographic features and various laboratory parameters were analyzed. At each routine hemodialysis visit, predialysis, intradialysis, and postdialysis blood pressure measurements were systematically conducted. A 24-hour ambulatory electrocardiogram (ECG) was performed during the hemodialysis interval, and heart rate variability (HRV) values were calculated. Additionally, whether the patients ate during the hemodialysis treatments was recorded. Another 20 people who underwent physical examinations during the same period and were matched for sex and age were included in the control group. The HRV values of the hemodialysis patients were generally lower than those of the control group. Univariate analysis revealed significant differences in sex, age, calcium antagonist use, blood calcium levels, insulin levels, diastolic blood pressure (DBP) measurements, and HRV indices between hemodialysis patients who ate and those who did not eat during hemodialysis (P < .05), whereas there were no significant differences in diabetes status or in the hemoglobin, albumin, blood glucose and C-peptide levels (P > .05). Multivariate analysis revealed that low values for very low frequency (VLF) and postdialysis DBP were risk factors for fasting intolerance during hemodialysis treatments. Autonomic dysfunction may affect whether hemodialysis patients tolerate fasting during dialysis. VLF evaluation may provide information that can be used to develop a more reasonable intradialytic nutritional supplementation method.

Dysfunction of the autonomic nervous system in gastro-esophageal reflux disease: Consequences for the cardiovascular system

ObjectiveThe pathophysiology of gastro esophageal reflux disease (GERD) implicates autonomic dysregulation of the lower esophageal sphincter tone. Our goal is to investigate whether this dysregulation of the autonomic nervous system (ANS) function observed in isolated GERD cases can affect other systems, such as cardiovascular regulation.Methods: Twenty-five participants were included in the study, 11 patients with isolated GERD and 14 controls. All patients and 7 controls responded to a COMposite Autonomic Symptoms Score 31 (COMPASS 31) questionnaire and underwent functional explorations including EMLA test, sympathetic skin response (SSR), 24-hour heart rate recording and ambulatory blood pressure measurement (ABPM). Seven additional controls underwent a 24-hour heart rate recording only. ResultsGERD patients (Age: mean 36.81±7.82; SR= 0.22) showed high clinically dysautonomic scores (COMPASS 31) (p = 0.015), increased Heart rate variability (HRV) parameters (daytime, nighttime, 24-hour SDNN (standard deviation of the RR interval (NN)), respectively p = 0.003, p < 0.001, p = 0.001; daytime and nighttime very low frequencies (VLF) respectively p = 0.03 and p = 0.007), impaired nocturnal dipping of blood pressure (3/11 patients) and high positivity of EMLA test (7/11, p = 0.037). These outcomes were strongly correlated with clinical dysautonomic assessment. No difference was observed between patients and controls regarding SSR. ConclusionOur data suggests a high parasympathetic tone amongst patients with GERD and a dysregulation of parasympathetic and sympathetic balance in the cardiovascular system with an impairment of the peripheral sympathetic fibers of cutaneous microcirculation, assessed by the EMLA test. GERD may be an inaugural symptom of autonomic neuropathy. Further functional exploration of peripheral small fibers seems to be necessary.

Performance Analysis and Optimization of Switch Device for VLF Communication Synchronous Tuning System Based on Coupled Inductors

The very low frequency (VLF) communication system is characterized by a limited transmit bandwidth. Due to the low operating frequency, the dimensions of VLF antennas are significantly smaller than the corresponding wavelength. Therefore, VLF antennas are considered electrically small antennas (ESAs) with high Q values and narrow bandwidth. To achieve broadband VLF communication, synchronous tuning technology is commonly employed. In this study, we focus on analyzing the performance of the switching device in the synchronous tuning system using coupled inductors and IGBT as core components. By considering the equivalent circuit of the controlled source associated with coupled inductors, we propose an adaptive input impedance optimization algorithm based on the variable capacitor (hereinafter referred to as VC-ADIO) to address issues arising from coupling coefficient variations and internal parameters within IGBTs that affect primary loop input impedance. The radiated power of the VLF antenna is improved effectively.

Spectra of GRB 221009A at Low Energies Derived from Ground-based Very Low-frequency Measurements

The gamma-ray burst (GRB) event GRB 221009A was the brightest event that has ever been detected to date. Owing to its unexpected brightness, the temporal and/or spectral information of the prompt emission cannot be accurately measured by many satellites (with the only exception of GECAM-C), since they suffered from significant pulse pileup and data saturation effects. Similarly, the X45 solar flare event occurring on 2003 November 4 saturated space-borne X-ray detectors, and it was through ground-based measurements of very low-frequency (VLF) signals that the magnitude of this event was determined, since VLF signals are particularly sensitive to the disturbance on the D-region ionosphere caused by low-energy photons. Therefore, in this study, we first report measurements of VLF signals from the JJI and VTX transmitter as recorded in Shiyan, China, when GRB 221009A occurred. The amplitude change was ∼1.25 and ∼2.31 dB for the JJI and VTX transmitter, respectively. Using a suite of well-validated models, we have further simulated the influence on the D-region ionosphere induced by low-energy photons (<100 keV) of GRB 221009A. Compared with the pre-GRB condition, the electron density was enhanced by 39.75% and 626.61% at 60 and 70 km altitude for the VTX-SYS path and 39.73% and 621.11% at 60 and 70 km altitude for the JJI-SYS path, respectively, with the altitude of notable electron density change being as low as ∼30 km. Moreover, we have compared modeling results of VLF signal change with our measurements during GRB 221009A. The good agreements obtained in terms of amplitude change and overall trend validate the fluxes and spectra of GRB 221009A at low energies (<20 keV) as measured by GECAM-C.

First observations of the transient luminous event effect on ionospheric Schumann resonance, based on the China Seismo-Electromagnetic Satellite

Abstract. In this study, we focus on the interactions and interrelated effects among the transient luminous events (TLEs) recorded at the Luoding ground station (22.76° N, 111.57° E), the lightning activities observed by the World Wide Lightning Location Network, and the ionospheric electric field deduced from the China Seismo-Electromagnetic Satellite (CSES). The results show that on 25 September 2021, the signal-to-noise ratio of the Schumann resonance at the first mode of 6.5 Hz and the second mode of 13 Hz dropped below 2.5 during the TLEs. A significant enhancement in the energy in extremely low frequencies (ELFs) occurred, and the power spectral density increased substantially. Distinct lightning whistler waves were found in the very low frequency (VLF) band, further indicating that the energy could possibly have been excited by the lightning. Our results suggest that the observations of the electric field from the satellite could possibly be utilised to monitor the lower-atmospheric lightning and its impact on the space environment.

Integration of Geophysical and Hydrochemical Methods to Determine the Groundwater Contamination in Al-Hosayniat Landfill South East Mafraq City, Jordan

An integration of Geophysical – Electromagnetic and hydro-chemical methods was used to investigate the potential of groundwater contamination due to Al-Hosayniat Municipal Landfill (HL) southeast of Mafraq city. Twenty-five Time Domain Electromagnetic (TDEM) soundings were carried out inside and outside the HL in addition to one WNW-ESE Very Low Frequency (VLF) profile. The TDEM's results help to define the subsurface geology and structures down to 240m depth. The results also depict the presence of a major fault striking NW-SE that crosses the whole landfill, this fault is documented in the surface geological map, and it was delineated and imaged by TDEM measurements and detected at larger depths. VLF results also detected the presence of a major fault beneath the landfill. The presence of the fault just beneath the HL may enhance the leachate movement which can imply groundwater contamination hazards for a longer period as it is a preferential pathway for contaminants. The results of water quality analyses of adjacent wells show higher concentrations of Na+, SO-24, TDS in some wells and this can be ascribed to agricultural activities and over-pumping in the area rather than landfill leachate. The heavy metal concentrations were found to be within the permissible limits and did't indicate direct contamination due to the HL. However, Fluorite (F-) shows a high concentration of (1.3mg/l) in WS4 and WS5 wells and approaches the permissible limit (1.5mg/l) according to the Jordan Water Standards (JWS). Bromide (Br) shows high concentration of (0.6mg/l) in well Al-2462.