A detailed investigation of low latitude tweek atmospherics observed by the WHU ELF/VLF receiver: 2. Occurrence features and associated ionospheric parameters

Abstract

As a companion paper to Zhou RX et al. (2020), this study describes application of the automatic detection and analysis module to identify all the tweek atmospherics detectible in the WHU ELF/VLF receiver data collected at Suizhou station during the period of 3 February through 29 February 2016. Detailed analysis of the identified low‐latitude tweek events reveals that the occurrence rate varies considerably — from 800 to 6000 tweeks per day, and exhibits a strong diurnal and local time dependence, the peak occurring before local midnight. The diurnal variation of identified tweeks was similar to that of the lightning data obtained by the World‐Wide Lightning Location Network (WWLLN).. Estimates of the propagation distance and ionospheric reflection height of tweek atmospherics suggest that the majority (~92%) of the low latitude tweeks originate from the lightning activity within a radius of 4000 km and that they are very likely to reflect from the lower ionospheric D‐region at the height range of 75–85 km. At these lower ionospheric reflection altitudes, ~74% of the corresponding electron densities from the tweek spectral measurements are within 24.5–27.5 cm ‐3. The daily variation of estimated D‐region electron densities in the considered period (February 2016) also exhibits a small overall increasing trend from early to later in the month.

A detailed investigation of low latitude tweek atmospherics observed by the WHU ELF/VLF receiver: I. Automatic detection and analysis method

“…While our study has adopted the model described by Equations (1)–(6) to estimate the tweek propagation distances and then obtain estimates of source lightning locations, it is important to compare our model results with direct observations of lightning activity, e.g., data from the WWLLN. Our companion paper (Yi J et al, 2020) has performed such an analysis for the period of this study, February 2016. It concludes that our ELF/VLF receiver at the Suizhou station captures a majority of tweek events with propagation distances < 4000 km, but does not detect as many lightning events at greater distances from Suizhou (i.e., > 4000 km) as are found in WWLLN data.…”

“…We also note that the present study utilizes only nighttime (i.e., 22–02 LT) data for analysis. The major reason is that the number of daytime tweeks is much lower than that of nighttime tweeks, as shown inFigure 1 of the companion paper (Yi J et al, 2020). Such a day‐night asymmetry of the occurrence pattern of tweeks can be well explained by the fact that the diurnal variation of the lower ionosphere is predominantly controlled by the abundance of sunlight.…”

“…By defining reasonable criteria, that is, that the distance relative difference be ≤ 0.3 and the correlation coefficients be ≥ 0.9, our established automatic detection and analysis method supplies a valuable means to investigate comprehensively the occurrence characteristics of low latitude tweek atmospherics. Its underlying sources and associated ionospheric parameters are evaluated in detail in a companion paper of Yi J et al (2020).…”

First Results of the Wave Measurements by the WHU VLF Wave Detection System at the Chinese Great Wall Station in Antarctica

“…The detection system has a high dynamic range of ∼110 dB, and thus the signal with a wide range of intensity variation can be sampled as completely as possible. With a dynamic range sensitivity of ∼110 dB and time accuracy of ∼100 ns, the WHU ELF/VLF receiving system enables the reception of artificial and natural VLF signals with resolutions that suffice most ionospheric and magnetospheric studies (Chen et al., 2017; Gu, Chen, et al., 2022; Gu, Li, et al., 2021; Gu, Luo, et al., 2021; Gu, Peng, et al., 2022; Wang et al., 2020; Yi et al., 2019, 2020; Zhou et al., 2020).…”

Statistical Analysis of Very Low Frequency Atmospheric Noise Caused by the Global Lightning Using Ground‐Based Observations in China

“…The Universal Time Coordinated (UTC), longitude and latitude, and high precision 1‐Pulse‐Per‐Second (1 PPS) timing signals required by the receiving system are all obtained by the standard GPS module. Due to the high dynamic range and time accuracy of the equipment, the WHU ELF/VLF receiving system can guarantee the reception of artificial VLF transmitter signals and natural VLF signals in high resolution (Chen et al., 2017; Gu, Luo, et al., 2021; Gu, Peng, et al., 2021; Wang et al., 2020; Yi et al., 2019, 2020; Zhou et al., 2020).…”