Measurements and Modeling of the Responses of VLF Transmitter Signals to X‐Class Solar Flares at the Great Wall Station in Antarctica

Xu, Wei; Gu, Xudong; Ni, Binbin; Wang, Shiwei; Yang, Zhenghong; Cheng, Wen; Hu, Zejun; He, Fang; Li, Bin; Chen, X.; Liu, Jianjun; Hu, Hongqiao

doi:10.1029/2022sw003249

Cited by 6 publications

(8 citation statements)

References 81 publications

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“…This receiver can detect VLF signals in the frequency range of 1–50 kHz (Gu, Wang, et al., 2022). This receiver is highly sensitive, with a dynamic range of ∼110 dB and a timing accuracy of ∼100 ns (Gu et al., 2023; Xu, Gu, et al., 2023). Two triangle‐shaped magnetic loop antennas were set up at the Suizhou station, one oriented along the East‐West direction and the other one along the North‐South direction (Gu, Wang, et al., 2022), constituting an orthogonal two‐channel system.…”

Section: Methodsmentioning

confidence: 99%

Periodic Oscillation of VLF Transmitter Signals Measured in Low and Middle Latitude Regions

Xu,

Feng,

et al. 2024

JGR Atmospheres

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Measurements of Very Low Frequency (VLF) signals from navy transmitters carry direct information about the D‐region ionosphere and have been widely utilized for detecting the electron density at D‐region altitudes, but not frequently for the atmospheric waves therein. Atmospheric waves have been extensively studied using the total ionospheric electron content, but if and how they are correlated with the D‐region ionosphere and VLF measurements still remains poorly investigated. In this study, we have conducted a comprehensive analysis using 7‐year measurements (2016–2022) of VLF signals from the JJI, NWC, and VTX transmitters as being recorded in Suizhou, China. These three transmitter‐receiver paths are representative and the corresponding observations constitute a valuable data set to investigate the periodicities of VLF data. Different from previous studies, we have utilized the ensemble empirical mode decomposition and Lomb‐Scargle methods to determine the periodicities of these data. By contrasting these paths, prominent periodicities ranging from 2 to 730 days have been found, with clear diurnal variation and suggestive latitudinal/longitudinal dependence. Moreover, we have found that the mesospheric temperature is closely related with the annual oscillation of VLF measurements, while this oscillation has a low correlation with solar Lyman‐α fluxes or geomagnetic activity. The oscillations with relatively shorter periods are likely atmospheric waves such as gravity waves, planetary waves, or harmonics of these waves. Our results suggest that, in addition to the electron density, the subionospheric VLF technique can be potentially utilized to remotely sense atmospheric waves that propagate up to or through the D‐region ionosphere.

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Section: Methodsmentioning

confidence: 99%

Periodic Oscillation of VLF Transmitter Signals Measured in Low and Middle Latitude Regions

Xu,

Feng,

et al. 2024

JGR Atmospheres

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“…This fact makes the amplitude and phase of VLF signals the effective tools for assessing the state and dynamics of the lower ionosphere in quiet and disturbed conditions (Gavrilov et al, 2019). For example, VLF signals are successfully used to verify theoretical models of the medium (Bekker et al, 2022;Bekker & Korsunskaya, 2023;Xu et al, 2021Xu et al, , 2023 and to estimate X-ray fluxes during solar flares of various classes (George et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Estimation of the Ionospheric D‐Region Ionization Caused by X‐Class Solar Flares Based on VLF Observations

Ryakhovsky,

Poklad,

Gavrilov

et al. 2024

JGR Space Physics

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In this paper, we study the ionization‐recombination processes in the lower ionosphere during solar flares of various classes in June 2014 and September 2017. For the first time, ionization and recombination rates of the ionospheric D‐region were estimated using the experimental data on variations in the amplitude and phase characteristics of very low frequencies (VLF) signals and two‐channel data from the GOES satellite (0.05–0.4 nm and 0.1–0.8 nm). The empirical two‐parameter Wait‐Ferguson model was used to calculate temporal changes in the electron concentration Ne during solar flares of different classes. GOES satellite data and black body model were used to estimate the X‐ray fluxes in the wavelength spectral range λ ≤ 0.3 nm. Joint analysis of the temporal evolution of the Ne vertical profile in the lower ionosphere and X‐ray fluxes in different wavelength ranges was carried out. As a result, the values of the ionization and recombination rate coefficients were obtained, and the spectral ranges of radiation that have the greatest impact on Ne at given heights were determined. Calculated ionization and recombination rate coefficients and ranges were successfully verified using VLF data during different solar flares. The results obtained in this work can be used in future studies for a more accurate assessment of the response of lower ionosphere to solar flares of various classes.

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“…The electron density in the D-region ionosphere is too low to be effectively measured by instruments that are specifically designed for other regions of the ionosphere [4,5]. Sudden perturbations in the D-region ionosphere could lead to abnormal changes in the VLF transmitter signals; for example, the electron density change at D-region altitudes produced by solar flares [6][7][8][9], solar eclipses [10,11], lightning discharge [12][13][14] and electron precipitation from the radiation belts [15]. Therefore, the VLF technique has been widely utilized to remotely sense the lower ionosphere and represents one of the most reliable and effective approaches for long-term observation of the D-region ionosphere [16][17][18][19].…”

Section: Introductionmentioning

confidence: 99%

Automatic Detection of VLF Tweek Signals Based on the YOLO Model

Xu,

Ma,

Wang

et al. 2023

Remote Sensing

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Tweek signals are a special type of VLF (very low frequency) pulse, originally produced by lightning discharge, which becomes dispersive after repetitive bounces within the waveguide between the Earth’s surface and lower ionosphere. As such, tweek signals carry critical information about the region near the reflection height of the VLF waves, namely the D-region ionosphere. Although tweek measurements have been widely utilized in studies of the D-region ionosphere and lightning discharge, few statistical studies have been conducted, mainly due to the difficulty of manually identifying tweek signals from the enormous amount of VLF data with heavy noise. Considering the importance of tweek signals and the lack of a high-precision detection model, in this study, we propose a method to automatically and accurately pick out tweek signals from VLF measurements. This method is explicitly developed based on the you only look once (YOLO) model and a post-tracing process. Using a total of 2495 randomly selected VLF spectrogram images as the testing set, we evaluated the performance of this method. The precision and recall are found to be 92.0% and 89.2% for the first-order mode, and 97.5% and 86.7% for the first-two-order mode tweek, respectively. The time needed to process 10-s VLF measurements with a cadence of 4 μs is only 6.5 s, allowing for identifying the tweek signals from continuous VLF measurements in real time. Therefore, this method represents a reliable means to automatically detect tweek signals and enables the opportunity to statistically investigate the D-region ionosphere and lightning discharge via these signals.

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Measurements and Modeling of the Responses of VLF Transmitter Signals to X‐Class Solar Flares at the Great Wall Station in Antarctica

Cited by 6 publications

References 81 publications

Periodic Oscillation of VLF Transmitter Signals Measured in Low and Middle Latitude Regions

Periodic Oscillation of VLF Transmitter Signals Measured in Low and Middle Latitude Regions

Estimation of the Ionospheric D‐Region Ionization Caused by X‐Class Solar Flares Based on VLF Observations

Automatic Detection of VLF Tweek Signals Based on the YOLO Model

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