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Ionospheric disturbances as precursor signals of the March 28, 2025, Myanmar earthquake
(2026-03-15)
Pansong, C.
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Ruttanaburee, S.
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Pornsopin, P.
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Kenpankho, P.
This study examined the ionospheric response associated with the Mw 7.7 Myanmar earthquake on March 28, 2025, using GPS-derived Total Electron Content (TEC) data from seven GNSS stations across Thailand. TEC variations were analyzed alongside Dst and Kp indices, as well as ionosonde-derived parameters, namely the critical frequency of the F2 layer (foF2), the peak height of the F2 layer (hmF2), the disturbances in NmF2, and the slab thickness (τ), which were obtained from three IGS-supported stations. We detected abnormal variations in TEC approximately 15 days before the earthquake (13–27 March 2025), characterized by alternating positive and negative deviations. The TEC exhibited alternating positive and negative deviations throughout the analysis period, reflecting ionospheric variability prior to the earthquake. During the early period (13–18 March), the deviations remained within approximately ±6 TECU. However, from 19 to 21 and 23–24 March, moderate fluctuations were observed, particularly at mid- and low-latitude stations (UTHG, THBK, THCP, and THPK), where ΔTEC ranged from ±6 to 10 TECU. The TEC decrease occurred on 25 March under weak geomagnetic conditions (Dst > −30 nT) at the northern stations MAEH (−18.40 TECU), THCM (−15.65 TECU), and NANN (−15.73 TECU), marking the most pronounced negative anomaly observed during the study period. Subsequently, on 26–27 March, TEC values recovered to positive anomalies of +4 to +10 TECU, indicating a return to normal ionospheric conditions. To objectively identify pre-seismic ionospheric anomalies, a Median Absolute Deviation (MAD) approach was applied using a ±1.34MAD threshold. This statistical technique effectively detects subtle deviations while minimizing transient noise. The results reveal coherent TEC depletions across multiple stations on 25 March, suggesting the presence of localized ionospheric disturbances potentially related to seismo-ionospheric processes rather than geomagnetic effects. Furthermore, concurrent anomalous increases in foF2 and hmF2, along with a reduction in slab thickness near the epicentral region, indicate vertical uplift of the F2 layer, consistent with possible Lithosphere–Atmosphere–Ionosphere Coupling (LAIC) mechanisms.
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Low-Latitude Ionospheric Responses to Two Matched Intense Equinoctial Geomagnetic Storms: A Case-Based Comparison Between Solar Cycles 24 and 25
(2026-01-16)
Pansong, Chollada
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Kenpankho, Prasert
This study investigates the ionospheric responses to two matched intense equinoctial geomagnetic storms that occurred during Solar Cycles 24 and 25 (SCs 24 and 25), with emphasis on variations in Total Electron Content (TEC), the F2-layer critical frequency (foF2), and the F2-layer peak height (hmF2). TEC data were derived from Global Ionospheric Maps (GIMs) based on Global Navigation Satellite System (GNSS) observations, while foF2 and hmF2 parameters were obtained from the Global Assimilative Model of the Bottomside Ionosphere Timeline (GAMBIT) for 22 low-latitude locations worldwide. The results show that the SC25 storm produced stronger and more spatially extensive ionospheric responses than the SC24 event. Peak TEC values during SC25 exceeded those of SC24 by up to ~80-90 TECU in the Southeast Asian, East Asian, and Pacific sectors near the storm main phase, indicating a pronounced positive ionospheric storm. These enhancements are closely associated with higher solar wind speeds (~650-700 km s<sup>–1</sup>) and strongly fluctuating IMF Bz during SC25, which generated sustained multi-pulse Prompt Penetration Electric Fields (PPEFs) that intensified E × B plasma drifts and the equatorial fountain effect. In contrast, SC24 was characterized by lower solar wind speeds (~550-600 km s<sup>–1</sup>) and a predominantly southward IMF Bz, resulting in shorter-lived PPEF activity, weaker TEC enhancements, and pronounced depletion during the recovery phase. Correlation analysis between Dst and TEC disturbances reveals strong negative correlations (r ≈ −0.6 to −0.9) in the Asia-Pacific sectors during the main phase, indicating that enhanced TEC disturbances tend to coincide with periods of increasing storm intensity, whereas predominantly positive correlations (r ≈ 0.6-0.9) are observed in the Middle Eastern-African-European sector, reflecting TEC depletion. The foF2 response shows clear phase dependence, with localized daytime enhancements during the main phase but widespread reductions of ~15-20% during recovery in both solar cycles, consistent with the influence of Disturbance Dynamo Electric Fields (DDEFs), and thermospheric composition changes. In contrast, hmF2 exhibits solar-cycle-dependent behavior, with modest increases (~3-8%) during SC24 and more variable, often negative responses (up to ~2-3% decrease) during SC25. These findings highlight the heterogeneous, region-dependent, and solar cycle-dependent nature of ionospheric variability during intense geomagnetic storms, with important implications for space weather modeling and prediction.
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GNSS Receiver Bias Model for Near Real Time TEC Monitoring at Low Latitude, Thailand
(2026-01-01)
Kenpankho, Prasert
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Maichuen, Samatchaya
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Phothila, Prarinya
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Zhang, Jianfeng
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Keokhumcheng, Thanapon
This research proposes and investigates GNSS receiver bias modeling for near real time total electron content (TEC) monitoring across 16 multi-frequency GNSS stations in low latitude, Thailand, from 2022-2024. By applying a refined methodology based on Kenpankho et al. (2021) and integrating IONOLAB-BIAS for single station bias estimation, the research corrects for satellite and receiver inter-frequency biases to enhance TEC accuracy. Results show a consistent upward trend in TEC values, reflecting increased latitudes, seasonal ionospheric activity, and geomagnetic storms. Comparative analysis with the IRI 2020 model using correlation coefficients and RMSE reveals spatial and temporal variation, with near equatorial latitude stations showing strong alignment than upper low latitude stations. The results highlight the importance of localized GNSS-based TEC models for improving satellite positioning accuracy in equatorial regions and highlight the limitations of global models under dynamic ionospheric conditions.
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Low latitude TEC disturbances during extreme geomagnetic storms: insights into March and May 2024
(2025-12-15)
Pansong, C.
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Wongsak, P.
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Ruttanaburee, S.
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Pornsopin, P.
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Kenpankho, P.
This study investigates the variations of the Total Electron Content (TEC) in response to the extreme geomagnetic storms at the low latitudes over Thailand in 2024. For analyzing data from geomagnetic storms recorded in March and May 2024, with Dst maximum to −412 nT and Kp index to 9 on May 11, 2024, Dst at −351 nT and Kp at 9- on May 10, 2024, Dst at −159 nT and Kp at 7 on May 12, 2024, and Dst at −128 nT and Kp at 8 + on March 24, 2024. This study conducted a 13-day analysis for maximum negative Dst storm event, encompassing six days before and six days after the event. Data were sourced from GNSS receiver stations at Chiang Mai (THCM: 19.21°N, 99.12°E, 9.96°N Dip), Bangkok (THBK: 13.73°N, 100.78°E, 4.82°N Dip), and Chumphon (THCP: 10.72°N, 99.38°E, 1.85°N Dip), Thailand. The study highlights a significant TEC disturbance that increases during the extreme geomagnetic storm, particularly at THCP, next to equatorial latitude. TEC increases at a heightened sensitivity to geomagnetic storms. As a result, TEC reached up to 60 TECU from the average TEC of the six previous days and six posterior days excluding the maximum storm event day at a low latitude. The intense nighttime geomagnetic storms were a few events that resulted in minimal TEC gap increases compared to the daytime geomagnetic storms. Additionally, the correlation coefficient between geomagnetic storm levels and TEC disturbances is strongly and significantly linked to storm intensity. The signature of TEC disturbance is influenced during extreme geomagnetic storms in the ascending phase of Solar Cycle 25 at low latitudes, emphasizing the importance of enhanced understanding of TEC behavior in low latitude regions.
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Spatio-temporal characteristics of ionospheric irregularities in low latitude regions during the peak of solar cycle 25
(2025-07-01)
Tongkasem, Napat
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Supnithi, Pornchai
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Thammavongsy, Phimmasone
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Nishioka, Michi
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Perwitasari, Septi
Equatorial plasma bubbles (EPBs) are a primary source of ionospheric irregularities (IIR) in low-latitude regions. The severity of EPBs depends on the intensity, penetration, and disturbance of electric fields generated in the ionosphere. In this work, we analyze the IIR associated with geomagnetic activity in the low-latitude region (0°N–25°N, 90°E–110°E) from 2022 to 2024. The total electron content (TEC) and the rate of TEC index (ROTI) are used to investigate the spatiotemporal characteristics of these IIRs, influenced by both local EPBs and global geomagnetic storms. During low-to-moderate geomagnetic activity, electric field penetration and disturbances have a low impact on EPB development. The high solar activity intensifies the electric field, leading to intense EPB occurrences that can affect the entire region for several hours. From January 2022 to October 2024, these intense EPB events accounted for 35% of all EPB occurrences. During strong geomagnetic storms, the prompt penetration of electric fields (PPEF), and disturbance dynamo electric field (DDEF) caused the depression and fluctuations of TECs.
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Multi-satellite based possible precursory signals detection linked to the 2024 Mw 7.5 Noto Peninsula Japan earthquake
(2025-06-15)
Shahzad, Rasim
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Shah, Munawar
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Nabi, Imtiaz
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Jamjareegulgarn, Punyawi
Satellite-based anomaly detection can provide substantial precursory information linked to impending earthquakes (EQ). The strong EQs are followed by some complex precursory signals both before and after the main shock. For this, different methods and datasets are employed to monitor these disastrous events. In our study, we used the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite to evaluate land surface temperature (LST), the Global Navigation Satellite System (GNSS) to observe total electron content (TEC) variations, Swarm satellites to monitor spatial variations in electron density, and Cosmic satellites were used to measure variations in the vertical profile of electron density to look for the complex precursors of Noto Peninsula Japan EQ of 7.5 Mw (occurred on 1st January 2024). Our objective was to observe both the pre- and post-EQ induced anomalies within 25 days and 10 days of the main shock by integrating the statistical, nonlinear autoregressive network with exogenous inputs (NARX) and continuous wavelet transformation (CWT) methods. We found synchronized and co-located pre-seismic anomalies on December 25 in LST, TEC and electron density. Which was further confirmed using NARX and CWT as well. Additionally, we found some potential post-seismic anomalies. There was an anomalous enhancement in daytime LST, TEC, and electron density on January 2nd with the exception of nighttime LST which showed abrupt increments on the night of the main shock (i.e., January 1st). These findings point towards the strong EQ-induced energy into the atmosphere and ionosphere for more prominent proof of lithosphere-atmosphere–ionosphere coupling (LAIC).
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Variations in Ionospheric Total Electron Content and Scintillation at GPS stations in Uzbekistan and China during the Annular Solar Eclipse on June 21, 2020
(2025-05-01)
Eshkuvatov, H. E.
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Jamjareegulgarn, Punyawi
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Ahmedov, B. J.
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Tillayev, Y. A.
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Ruziev, Z. J.
This study presents a novel investigation into the distinct ionospheric variations observed over China and Uzbekistan during the annular solar eclipse on June 21, 2020. For the first time, we demonstrate the influence of this celestial event on Total Electron Content (TEC) measurements obtained from GPS satellites. We analyzed fluctuations in TEC and the Ionospheric Scintillation Index (S4) across six strategically selected sites—three in Uzbekistan (MTAL, KIT3, MADK) and three in China (JFNG, LHAZ, BJFS) located near the eclipse path, with obscuration levels of 52%, 57%, 58%, in Uzbekistan and 92%, 94% and 95% in China. Our study involved continuous monitoring of ionospheric parameters over three days, from June 20 to June 22, 2020. Results indicated a significant TEC depletion ranging from 10% to 30% on the day of the eclipse. The analysis reveals that both TEC levels and the S4 scintillation index experienced notable reductions during the event, attributed to the decreased ionizing radiation. These findings enhance our understanding of ionospheric dynamics in response to solar eclipses and have important implications for satellite communication and navigation systems.
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The study on the relationship between ionospheric delay and low-cost localizing robots
(2025-03-01)
Sumniang, Patiphan
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Sittichai, Wishapol
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Kenpankho, Prasert
The dispersive and anisotropic nature of the ionosphere above certain regions particularly on Thailand's low − nearly equatorial − latitude, positioning accuracy is seriously affected when using a precision limited model. Change in ionospheric delay is a key factor impacting the Global Navigation Satellite Systems (GNSS) positioning and navigation accuracy. We studied the effect of ionospheric delay on localizing low-cost robots. We investigated the positioning error using ionospheric delay from a GNSS receiver, IRI and our campus, KMITL, in Bangkok, to guide our ‘G-LOC’ robot. There were eight target points, set from 3 to 50 m at the same meridian with varying latitudes. Impacts on a robot moving on low solar activity days, high solar activity days, daytime, and nighttime were measured over 12 months in 2023. We found that high solar activity day impacts a robot moving on highest accuracy error up to 363 cm at high speed. In addition, we found that daytime impacts a robot moving on highest accuracy error up to 154.05 cm at high speed as well. Ionospheric delay according to high and low solar activities, and daytime, and nighttime effects on the GNSS interference transmitted to a low-cost localizing robot was expected to affect moving errors, but it did not seem to lead to a significant difference in error between the low and high solar activity days.
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Predicting Equatorial Ionospheric Total Electron Content Using the Transformer-based Model with Observations From Ground GNSS Receivers and COSMIC-2 Satellites
(2025-01-01)
Mutasov, Gleb
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Supnithi, Pornchai
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Budtho, Jirapoom
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Perwitasari, Septi
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Nishioka, Michi
Ionospheric Total Electron Content (TEC) is a key parameter for monitoring and studying the ionosphere, which induces significant delays in radio signals. Equatorial ionospheric irregularities, such as Equatorial plasma bubbles (EPB), can severely disrupt satellite navigation and communication. Predicting TEC is, therefore, essential for space weather monitoring and high-precision positioning applications. This study employs a Transformer-based model to predict TEC 24 hours in advance for specific satellites based on observations from a ground station and COSMIC-2 satellites. Unlike other approaches, our model directly forecasts TEC values for visible satellites within predefined longitude-latitude ranges. To enhance predictive accuracy, we also integrate additional features: ionospheric pierce points (IPP), geomagnetic (HP60), and solar activity indices, utilizing time-series Transformer architecture, and we consider a long-short-term memory (LSTM) model as a baseline. The proposed approach provides promising results for local TEC forecasting in the specific coverage area, with potential for further enhancements using additional GNSS or TEC measurements.
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Simultaneous equatorial plasma bubble observation using amplitude scintillations from GNSS and LEO satellites in low-latitude region
(2023-12-01)
Seechai, Khanitin
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Myint, Lin Min Min
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Hozumi, Kornyanat
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Nishioka, Michi
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Saito, Susumu
This study estimates the scale sizes of the plasma density irregularities and the longitudinal width associated with equatorial plasma bubbles (EPBs) in equatorial and low-latitude regions. By analyzing amplitude scintillation S<inf>4</inf> indices and total electron content (TEC) measured from low earth orbit (LEO) satellite’s beacon signals with 400 MHz and Global Navigation Satellite System (GNSS) L1/E1 signals with 1575.42 MHz, recorded by receivers at the KMITL station in Bangkok, Thailand (geographic; 13.73° N, 100.77°E, magnetic: 7.26°N), we investigate the characteristics of these irregularities. We collected data of 154 LEO satellite pass events during nighttime on 21 disturbed days in four equinoctial months in 2021. Based on the presence or absence of the scintillation effects on GNSS and LEO beacon signals, the events are categorized into four classes to estimate the scale size of the plasma density irregularities. The analysis suggests that events with both GNSS and LEO scintillations, as well as events with GNSS scintillation alone, occur predominantly before midnight assuming the presence of the small-scale size of the irregularities within EPB. However, events with only LEO scintillation occur throughout the whole night and some events are observed before the events with both GNSS and LEO scintillations. Post-sunset LEO scintillation alone may be attributed to the onset of EPBs developing at low altitude, while post-midnight LEO scintillation events near the magnetic equator, observed during periods of low GNSS Rate of TEC Index (ROTI) values, are associated with bottom-side ionospheric irregularities but are not linked with EPB. The findings are consistent with previous researches on the generation and decay of electron density irregularities within plasma bubbles. However, this study provides new insights by using specific data sets and analysis techniques, offering a more comprehensive understanding of the association of LEO scintillations with bottom-side ionospheric irregularities near the magnetic equator, not observed in the ROTI map. Graphical Abstract: [Figure not available: see fulltext.]

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