Total Electron Content Fluctuations Research Articles

Strong ionospheric activity at the MWA site associated with plasma bubble measured by GNSS

Abstract The Earth’s ionosphere refracts radio signals, shifting the apparent position of radio sources. Wide-field measurements with a radio interferometer can measure the ionospheric distortion. The Murchison Widefield Array (MWA) has the ability to capture ionospheric structures that are smaller than $100\:$km in extent. We report unusually strong ionospheric activity in MWA data during a magnetic storm on 2023 December 1. The duct-like structure (roughly $50\: {\rm km} \times {>}100\:$km) passes through the MWA field-of-view with a velocity of ${\sim}100\:\mathrm{m}\:\mathrm{s}^{-1}$. The offsets of the apparent position of the radio source are more than $1^{\circ }$ in the MWA observation data at around $180\:$MHz. By comparing the total electron content (TEC) data obtained from the global navigation satellite systems’ receiver network, we have found that the TEC fluctuations represented by a high rate of TEC change index coincided with the strong ionospheric activity observed by the MWA. This result suggests that unusual ionospheric signatures detected by the MWA could be caused by plasma bubbles extending across Western Australia during a magnetic storm.

Variation of Total Electron Content over May 10 - 13 2024 Geomagnetic Super Storm in South Africa

This study investigates the variation of Total Electron Content (TEC) over South Africa during the geomagnetic superstorm of May 10 - 13, 2024. This study aims to analyze the variation of TEC over South Africa during the May 10 - 13, 2024, geomagnetic superstorm using data from the IRI-2020 model, GNSS-based TEC measurements, and other geomagnetic parameters. The root mean square error (RMSE) method was applied to quantify the deviations between GPS-derived TEC measurements and the IRI-2020 model during the geomagnetic storm. The results reveal significant TEC fluctuations, with a pronounced increase during the main phase due to prompt penetration electric fields (PPEFs) and storm-induced ionospheric disturbances. This was followed by a sharp TEC depletion in the recovery phase, attributed to thermospheric composition changes, particularly oxygen-to-nitrogen ratio variations. Magnetometer H-component observations further confirm the strong geomagnetic activity associated with the storm, indicating enhanced ionospheric currents and electrodynamic coupling. Latitudinal variations in TEC revealed complex ionospheric dynamics, with more pronounced disturbances at mid-latitudes. The ionospheric irregularities affected GNSS-based positioning, highlighting the impact of geomagnetic storms on navigation systems. These findings provide valuable insights into ionospheric storm effects over South Africa, contributing to improved space weather forecasting, GNSS accuracy, and regional ionospheric modeling.

Ionospheric Disturbances Detection Based on BDS‐GEO Observations With Prophet Model Over China: A Case Study of May 2017 Geomagnetic Storm

AbstractWe investigate ionospheric disturbances over China during the May 2017 geomagnetic storm using an integrated data set, including total electron content (TEC) measurements from BeiDou Navigation Satellite System's (BDS) Geostationary Earth Orbit (GEO) observations, ionosonde data, Swarm satellites, and global navigation satellite system (GNSS) radio occultation (RO) data. TEC anomalies were identified using the Prophet forecasting model, and results were compared with three sliding time window methods, showing consistent outcomes. The significant TEC increase during the storm's main phase was driven by prompt penetration electric fields (PPEF) linked to interplanetary magnetic field (IMF) Bz fluctuations. During the recovery phase, TEC increased on May 29 night, associated with southward IMF Bz turning and westward PPEF. Notably, the TEC negative storm observed at the KUN1 station on the morning of May 29 was likely caused by F‐layer uplift driven by the eastward overshielding electric field (OPEF) during the recovery phase, which induced Rayleigh‐Taylor instability and resulted in the formation of plasma bubbles. Additionally, the electron density (Ne) measured by COSMIC and Swarm satellites, along with ionospheric F2 layer parameters critical frequency (foF2) and peak height (hmF2) showed significant increases during the storm. A negative ionospheric response was observed over China on May 30 from 00:00 to 12:00 UT, likely caused by thermosphere composition changes. This study highlights the efficiency of BDS‐GEO satellites in monitoring ionospheric TEC variations, capturing spatiotemporal characteristics of disturbances, and validating the Prophet model for detecting anomalous TEC fluctuations during geomagnetic storms.

Ionospheric Irregularities Coinciding With the 2023 Typhoon Saola: A Multi‐Instrument Study

AbstractTyphoons exert significant influences on the ionosphere through atmospheric waves, ultimately affecting radio signals in the L‐band of the Global Navigation Satellite System (GNSS). Due to the limitations of ground observations, the mechanisms and full impacts of typhoon‐induced ionospheric variation remain to be explored. To address this gap, we embarked on a challenging expedition, employing a shipborne ionospheric scintillation monitoring receiver (ISMR) to gather data near the trajectory of Typhoon Saola during August and September 2023. The results revealed prominent amplitude scintillation and total electron content fluctuations in GNSS satellite detections, particularly during sunset from 29 to 31 August 2023. The findings are cross‐validated with ground GNSS stations, high‐frequency radar and the Swarm satellite, confirming the presence of equatorial plasma bubbles (EPBs). These EPBs have demonstrable effects on GNSS signals, ultimately influencing the precision of positioning performance. By examining the influence of the neutral wind field on atmospheric gravity waves triggered by typhoons, we elucidated how these waves impact the ionosphere, ultimately leading to the formation of plasma bubbles.

Impact of the October 28, 2021 Solar Flare and the November 4, 2021 Geomagnetic Storm on the Low, Middle, and High-Latitude Ionosphere

This study examines the ionospheric Total Electron Content (TEC) responses to a solar flare on October 28, 2021, and a geomagnetic storm on November 4, 2021, across low, middle, and high latitude regions. We utilized GPS-TEC data from the University NAVSTAR Consortium’s dual-frequency GPS devices at the IFR1, IISC, YIBL, YKRO, KERG, and SVTL stations. While the solar flare on October 28, 2021, triggered the geomagnetic storm on November 4, 2021, our analysis revealed notable TEC changes during the latter event. TEC fluctuations were observed across all stations during the geomagnetic storm, with significant disruptions and variable depletion rates. However, distinct TEC variations were noted at KERG and YIBL stations before the storm, likely due to the preceding solar flare. Continuous wavelet analysis (CWT) showed higher periodicity during the storm compared to the flare, proving CWT to be an effective tool for analyzing TEC variability by revealing periodicity fluctuations at all stations. In conclusion, we found that both solar flares and geomagnetic storms can cause significant positive TEC changes.

Assessment of Satellite Differential Code Biases and Regional Ionospheric Modeling Using Carrier-Smoothed Code of BDS GEO and IGSO Satellites

The geostationary earth orbit (GEO) represents a distinctive geosynchronous orbit situated in the Earth’s equatorial plane, providing an excellent platform for long-term monitoring of ionospheric total electron content (TEC) at a quasi-invariant ionospheric pierce point (IPP). With GEO satellites having limited dual-frequency coverage, the inclined geosynchronous orbit (IGSO) emerges as a valuable resource for ionospheric modeling across a broad range of latitudes. This article evaluates satellite differential code biases (DCB) of BDS high-orbit satellites (GEO and IGSO) and assesses regional ionospheric modeling utilizing data from international GNSS services through a refined polynomial method. Results from a 48-day observation period show a stability of approximately 2.0 ns in BDS satellite DCBs across various frequency signals, correlating with the available GNSS stations and satellites. A comparative analysis between GEO and IGSO satellites in BDS2 and BDS3 reveals no significant systematic bias in satellite DCB estimations. Furthermore, high-orbit BDS satellites exhibit considerable potential for promptly detecting high-resolution fluctuations in vertical TECs compared to conventional geomagnetic activity indicators like Kp or Dst. This research also offers valuable insights into ionospheric responses over mid-latitude regions during the March 2024 geomagnetic storm, utilizing TEC estimates derived from BDS GEO and IGSO satellites.

Earthquake source impacts on the generation and propagation of seismic infrasound to the upper atmosphere

SUMMARY Earthquakes with moment magnitude (Mw) ranging from 6.5 to 7.0 have been observed to generate sufficiently strong acoustic waves (AWs) in the upper atmosphere. These AWs are detectable in Global Navigation Satellite System satellite signals-based total electron content (TEC) observations in the ionosphere at altitudes ∼250–300 km. However, the specific earthquake source parameters that influence the detectability and characteristics of AWs are not comprehensively understood. Here, we extend our approach of coupled earthquake-atmosphere dynamics modelling by combing dynamic rupture and seismic wave propagation simulations with 2-D and 3-D atmospheric numerical models, to investigate how the characteristics of earthquakes impact the generation and propagation of AWs. We developed a set of idealized dynamic rupture models varying faulting types and fault sizes, hypocentral depths and stress drops. We focus on earthquakes of Mw 6.0–6.5, which are considered the smallest detectable with TEC, and find that the resulting AWs undergo non-linear evolution and form acoustic shock N waves reaching thermosphere at ∼90–140 km. The results reveal that the magnitude of the earthquakes is not the sole or primary factor determining the amplitudes of AWs in the upper atmosphere. Instead, various earthquake source characteristics, including the direction of rupture propagation, the polarity of seismic wave imprints on the surface, earthquake mechanism, stress drop and radiated energy, significantly influence the amplitudes and periods of AWs. The simulation results are also compared with observed TEC fluctuations from AWs generated by the 2023 Mw 6.2 Suzu (Japan) earthquake, finding preliminary agreement in terms of model-predicted signal periods and amplitudes. Understanding these nuanced relationships between earthquake source parameters and AW characteristics is essential for refining our ability to detect and interpret AW signals in the ionosphere.

Investigation into potential TEC changes due to 9 seismic tremors of 2021–2022

This research document delves into the analysis of alterations in Total Electron Content (TEC) as identified through GPS observations leading up to nine earthquakes that transpired between the late months of 2021 and 2022. The comprehensive study investigates the TEC variations and provides a detailed examination of heat maps centred around the earthquake epicentres. These heat maps, characterized by diverse latitudes and longitudes, play a pivotal role in validating the precise locations of the earthquake epicentres. Notably, the examination of these maps unveils discernible GPS TEC variations several days before the occurrence of each earthquake. In addition to the TEC analysis, the research sheds light on the fluctuations in solar magnetic parameters. The study elucidates instances where TEC peaks surpassed normal values, particularly during periods characterized by minimal solar radiation effects. This correlation between solar magnetic parameters and TEC fluctuations adds a nuanced layer to the understanding of the complex interplay of factors leading to seismic events. The cumulative findings derived from the investigation point towards a compelling conclusion: GPS TEC observations and the analysis of heat maps serve as indispensable indicators for identifying precursory signs that precede an impending earthquake. This multidimensional approach enhances our comprehension of the temporal and spatial aspects of seismic activity and underscores the potential significance of solar magnetic parameters in influencing such geophysical events.

Long-term equatorial ionosphere variations over Ethiopia

Long-term equatorial ionosphere variations over Ethiopia

Statistical Study of the Ionospheric Slab Thickness at Beijing Midlatitude Station

The ratio of the total electron content (TEC) to the F2-layer peak electron density (NmF2) is known as the ionospheric equivalent slab thickness (EST, also known as τ), and it is a crucial indicator of the ionosphere. Using TEC and NmF2 data from the years 2010 to 2017, this work conducts a comprehensive statistical analysis of the ionospheric slab thickness in Beijing, which is in the midlatitude of East Asia. The outcomes show that the τ have different diurnal variations at different seasons for high/low-solar-activity years. On the whole, daytime τ significantly greater than nighttime τ in summer, and it is the opposite for the τ in winter regardless of the solar cycle, whereas the τ during equinox shows different morphology for high/low-solar-activity years. Specifically, daytime τ is larger than nighttime τ during equinox in years of high-solar activity, while the opposite situation applies for the τ during equinox in years of low-solar activity. Moreover, the pre-sunrise and post-sunset peaks are most pronounced during winter for low-solar-activity years. In summer, there is a great increase in τ during the morning hours when compared with other seasons. Furthermore, the τ decreases with the solar activity during nighttime, whereas it seems there is no correlation between daytime τ and solar activity. This paper explained the primary diurnal variations in τ across different seasons during high-/low-solar-activity years by analyzing relative fluctuations of TEC and NmF2 throughout the corresponding period. In addition, based on the disturbance index (DI), which is calculated by instantaneous τ and its corresponding median, this paper found that the storm-time τ might increase when compared with its median value during the daytime, while it may both increase and decrease during the nighttime, especially around dawn and dusk hours. To further analyze the physical mechanism, an example on 2 October 2013 is also presented. The results indicate that the positive disturbance of τ during the main phase of a geomagnetic storm might be caused by the prompt penetration electric field and neutral wind during the storm, and the τ increases during the early recovery phase might be due to the disturbance dynamo electric field as well as the neutral wind during the storm. Moreover, there is a negative disturbance of τ in the recovery phase during the most disturbed sunrise hours, and it might be due to the electric field reversal, neutral wind or other factors during this period. This paper notes the differences of τ in midlatitude between different longitudinal sectors from the related climatology and storm-time behavior, as it would be helpful to improve the current understanding of τ at midlatitudes in East Asia.

Ionospheric irregularities observed during the geomagnetic storm of March 2015 and June 2015 over Ethiopia

Ionospheric irregularities observed during the geomagnetic storm of March 2015 and June 2015 over Ethiopia

TEC and ROTI Measurements from a New GPS Receiver at BOWEN University, Nigeria

Scintillation and total electron content (TEC) are the two major examples of the top-side ionospheric parameters that are recorded differently by most Global Positioning System (GPS) receivers. The new GPS sensor created by the Atmospheric and Space Technology Research Associates (ASTRA), Cornell University, and the University of Texas, Austin have capability to record scintillation and TEC fluctuations simultaneously. Hence, the Connected Autonomous Space Environment Sensor (CASES) from ASTRA is a software-defined GPS receiver with the dual frequency of L1 C/A and L2C codes for space-weather monitoring and can be remotely programmed via an internet source. The receiver employs numerous novel techniques that make it suitable for space-weather studies compared to other nearby GPS receivers, such as different methods for eliminating local clock effects, an advanced triggering mechanism for determining scintillation onset, data buffering to permit observation of the prelude to scintillation, and data-bit prediction and wipe-off for robust tracking. Moreover, the CASES hardware is made up of a custom-built dual frequency, a digital signal processor board, and a “single board computer” with an ARM microcontroller. We have used the CASES GPS receiver newly installed at Bowen University, Iwo, Nigeria, to investigate the TEC and the rate of the TEC index (ROTI) around the equatorial region. Measurements of the TEC and ROTI showed similar variation trends in monthly, seasonal, and annual periods when compared to TEC and ROTI measurements from a nearby station, BJCO at Cotonou, Benin Republic. The newly installed GPS receiver looks promising for scientific use as it is the only one operational in Nigeria at the moment.

Statistical Study of Global Lightning Activity and Thunderstorm‐Induced Gravity Waves in the Ionosphere Using WWLLN and GNSS‐TEC

AbstractWe present a statistical study of global lightning activity and correlate this activity with ionospheric fluctuations in the Total Electron Content (TEC). Thunderstorms play a significant role in modulating the ionosphere's plasma distribution. Using the well‐known World Wide Lightning Location Network (WWLLN) system, we investigate the diurnal, monthly, and seasonal variations in lightning stroke numbers across six continents. Typically, the monsoon causes a significant increase in lightning occurrences, as reflected in the WWLLN observations. We chose a time frame of July–December 2019, which usually covers the peak and post‐monsoon seasons on all the continents. The diurnal lightning activity is observed to be highest in the early afternoon for all the locations. In addition, we observe hemispherical changes in lightning activity that appear opposite in nature. Using the Global Navigation Satellite System (GNSS)‐International GNSS Service data, we use the Vertical TEC (VTEC) and Rate of change Of TEC Index as proxies for the amplitude scintillation S4 index. Using the wavelet analysis of the small‐scale fluctuations in the VTEC profile, we provide a time series analysis of wave‐like TEC fluctuations alongside lightning stroke count as a proxy for thunderstorm activity. It is found that, in most cases, Traveling Ionospheric Disturbances (TIDs) or a local maximum of small‐scale fluctuation in VTEC (dVTEC) that could be coupled to atmospheric gravity waves are observed during periods of peak thunderstorm activity. Most of the locations show that the spectral power of TIDs and the stroke energy density are highly correlated.

Spatial and Temporal Distributions of Ionospheric Irregularities Derived from Regional and Global ROTI Maps

Major advancements in the monitoring of both the occurrence and impacts of space weather can be made by evaluating the occurrence and distribution of ionospheric disturbances. Previous studies have shown that the fluctuations in total electron content (TEC) values estimated from Global Navigation Satellite System (GNSS) observations clearly exhibit the intensity levels of ionospheric irregularities, which vary continuously in both time and space. The duration and intensity of perturbations depend on the geographic location. They are also dependent on the physical activities of the Sun, the Earth’s magnetic activities, as well as the process of transferring energy from the Sun to the Earth. The aim of this study is to establish ionospheric irregularity maps using ROTI (rate of TEC index) values derived from conventional dual-frequency GNSS measurements (30-s interval). The research areas are located in Southeast Asia (15°S–25°N latitude and 95°E–115°E longitude), which is heavily affected by ionospheric scintillations, as well as in other regions around the globe. The regional ROTI map of Southeast Asia clearly indicates that ionospheric disturbances in this region are dominantly concentrated around the two equatorial ionization anomaly (EIA) crests, occurring mainly during the evening hours. Meanwhile, the global ROTI maps reveal the spatial and temporal distributions of ionospheric scintillations. Within the equatorial region, South America is the most vulnerable area (22.6% of total irregularities), followed by West Africa (8.2%), Southeast Asia (4.7%), East Africa (4.1%), the Pacific (3.8%), and South Asia (2.3%). The generated maps show that the scintillation occurrence is low in the mid-latitude areas during the last solar cycle. In the polar regions, ionospheric irregularities occur at any time of the day. To compare ionospheric disturbances between regions, the Earth is divided into ten sectors and their irregularity coefficients are calculated accordingly. The quantification of the degrees of disturbance reveals that about 58 times more ionospheric irregularities are observed in South America than in the southern mid-latitudes (least affected region). The irregularity coefficients in order from largest to smallest are as follows: South America, 3.49; the Arctic, 1.94; West Africa, 1.77; Southeast Asia, 1.27; South Asia, 1.24; the Antarctic, 1.10; East Africa, 0.89; the Pacific, 0.32; northern mid-latitudes, 0.15; southern mid-latitudes, 0.06.

Direct Connection Between Auroral Oval Streamers/Flow Channels and Equatorward Traveling Ionospheric Disturbances

We use simultaneous auroral imaging, radar flows, and total electron content (TEC) measurements over Alaska to examine whether there is a direct connection of large-scale traveling ionospheric disturbances (LSTIDs) to auroral streamers and associated flow channels having significant ground magnetic decreases. Observations from seven nights with clearly observable flow channels and/or auroral streamers were selected for analysis. Auroral observations allow identification of streamers, and TEC observations detect ionization enhancements associated with streamer electron precipitation. Radar observations allow direct detection of flow channels. The TEC observations show direct connection of streamers to TIDs propagating equatorward from the equatorward boundary of the auroral oval. The TIDs are also distinguished from the streamers to which they connect by their wave-like TEC fluctuations moving more slowly equatorward than the TEC enhancements from streamer electron precipitation. TIDs previously observed propagating equatorward from the auroral oval have been identified as LSTIDs. Thus, the TIDs here are likely LSTIDs, but we lack sufficient TEC coverage necessary to demonstrate that they are indeed large scale. Furthermore, each of our events shows TID’s connection to groups of a few streamers and flow channels over a period in the order of 15 min and a longitude range of ∼15–20°, and not to single streamers. (Groups of streamers are common during substorms. However, it is not currently known if streamers and associated flow channels typically occur in such groups.) We also find evidence that a flow channel must lead to a sufficiently large ionospheric current for it to lead to a detectable LSTID, with a few tens of nT ground magnetic field decreases not being sufficient.

Observational study of ionosphere TEC fluctuations triggered by interplanetary shock

<p indent=0mm>Interplanetary shocks can cause violent disturbances in near-earth space. In this paper, we use high time-resolution <sc>(1 s)</sc> data from ground-based global position system (GPS) receivers to analyze the perturbations of ionosphere total electron content (TEC) when an interplanetary shock impacted the Earth’s magnetosphere on March 17, 2015. We found that after the shock arrived at the Earth, TEC perturbations demonstrated the characteristics of ULF waves, and the fluctuation characteristics were different in different latitude regions. The amplitude of TEC fluctuations observed by the receivers in the polar region was approximately 0.4 TECU, which lasted for more than <sc>10 min,</sc> and the fluctuation period was 2 to <sc>3 min,</sc> which increased with the increasing latitude of the pierce point. The amplitude of the TEC fluctuations observed by the receivers in middle and low latitude areas was approximately 0.2 TECU, which lasted for 5 to <sc>10 min,</sc> and the fluctuation period was approximately 2 min. We suggest that the existence of plasmasphere may be the reason for such difference in TEC fluctuations, and that the TEC fluctuations in polar regions may be related to field line resonances. The TEC fluctuations in the middle and low latitude areas may be related to cavity mode oscillations. We used GPS TEC technology to detect ionosphere TEC fluctuations triggered by interplanetary shock, which can help us further understand the nature of ULF waves in the Earth’s magnetospheric-ionospheric system and can further demonstrate the important role of GPS TEC technology in the study of the near-earth space environment.

Ionosphere Anomaly Analysis before Earthquake Using GPS (Case Study: Banten Earthquake August 2nd, 2019)

This research is to analyze anomalies in the ionosphere that occur when an earthquake occurs. When an earthquake occurs, three types of waves are generated, namely: acoustic waves, gravity waves, and reyleigh waves. Acoustic waves generated perpendicularly from the earth’s crust during an earthquake propagate into the ionosphere, where they create electron density deviations. This phenomenon is detected as CIDs (Coseismic Ionosphere Disturbances), namely TEC (Total Electron Content) fluctuations that occur 15 minutes to 1 hour after an earthquake occurs. As a result of this deviation, the electromagnetic waves emitted by the GNSS (Global Navigation Satellite System) satellite will delay when passing through an ionosphere of approximately 300 km from the earth’s surface. The earthquake data used in this study came from earthquakes in Indonesia with the potential for a tsunami, namely the Banten earthquake on August 2, 2019 (7.4Mw from BMKG) with GNSS data from the closest CORS station to the epicenter, namely the CPTN, CPTU, and CUJG stations. The processing results show that there is a TEC anomaly recorded by GPS satellite no. 29 which appears 15-20 minutes after the earthquake. Anomalies ionosphere that occurs during an earthquake are expected to be useful as an early warning system before a tsunami happened.

Model-based reproduction and validation of the total spectra of a\xa0solar flare and their impact on the global environment at the X9.3 event of September 6, 2017

We attempted to reproduce the total electron content (TEC) variation in the Earth's atmosphere from the temporal variation of the solar flare spectrum of the X9.3 flare on September 6, 2017. The flare spectrum from the Flare Irradiance Spectral Model (FISM), and the flare spectrum from the 1D hydrodynamic model, which considers the physics of plasma in the flare loop, are used in the GAIA model, which is a simulation model of the Earth's whole atmosphere and ionosphere, to calculate the TEC difference. We then compared these results with the observed TEC. When we used the FISM flare spectrum, the difference in TEC from the background was in a good agreement with the observation. However, when the flare spectrum of the 1D-hydrodynamic model was used, the result varied depending on the presence or absence of the background. This difference depending on the models is considered to represent which extreme ultraviolet (EUV) radiation is primarily responsible for increasing TEC. From the flare spectrum obtained from these models and the calculation result of TEC fluctuation using GAIA, it is considered that the enhancement in EUV emission by approximately 15–35 nm mainly contributes in increasing TEC rather than that of X-ray emission, which is thought to be mainly responsible for sudden ionospheric disturbance. In addition, from the altitude/wavelength distribution of the ionization rate of Earth's atmosphere by GAIA (Ground-to-topside Atmosphere and Ionosphere model for Aeronomy), it was found that EUV radiation of approximately 15–35 nm affects a wide altitude range of 120–300 km, and TEC enhancement is mainly caused by the ionization of nitrogen molecules.

Impact of Hurricane Michael (2018) on local vertical total electron content

An analysis of vertical total electron content (TEC) estimates from the MIT Madrigal database is performed for the regions surrounding the eye of Hurricane Michael (2018). Absolute and detrended TEC values show a noticeable increase during the tropical cyclone (TC) relative to fluctuations at the same locations prior to the storm. Direct comparisons of TEC perturbation magnitudes to the number of lightning flashes in 1°×1° latitude-longitude boxes surrounding the eye of Hurricane Michael for each 5 min period of 10 October 2018 showed no visible trends. A similar comparison of the vertical TEC fluctuations with respect to the rainfall rates showed a positive correlation as the rainfall rate increased from light to moderate. However, a decrease in TEC perturbations were observed for the most intense rainfall rates. Additionally, ionosonde measurements in the Gulf of Mexico Region reveal an increased production of waves with periods less than 90 min after TC formation. These results indicate that the measured TEC fluctuations are most likely caused by atmospheric gravity waves produced by Hurricane Michael, which supports previous research.

Investigation of the characteristics of wavelike oscillations of post-sunset equatorial ionospheric irregularity by decomposing fluctuating TEC

Investigation of the characteristics of wavelike oscillations of post-sunset equatorial ionospheric irregularity by decomposing fluctuating TEC