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Analysis of ionospheric and geomagnetic fields changes in Thailand during the May 2024 geomagnetic storm
(2025-12-15)
Myint, Lin M.M.
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Perwitasari, Septi
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Nishioka, Michi
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Saito, Susumu
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Kaewthongrach, Rungnapa
The extreme geomagnetic storm of May 2024, the most severe in two decades of space weather history up to date, had widespread effects on the ionosphere, from the polar regions to the magnetic equator. This study examines the responses of the equatorial ionosphere and geomagnetic field over Thailand during this geomagnetic storm, utilizing data from GNSS receivers, magnetometers, and ionosondes near the magnetic equator and low-latitude regions of Thailand. We analyze the direct and indirect impacts of interplanetary magnetic field (IMF) and interplanetary electric field (IEF) variations, driven by solar storms, on local equatorial magnetic fields and ionospheric parameters. Our finding reveals that storm-driven electric fields, particularly prompt penetration electric fields (PPEF) and disturbance dynamo electric fields (DDEF), strongly influenced equatorial electric field (EEF), causing notable fluctuations in total electron content (TEC), critical frequency of F2 (foF2), and virtual height of F layer (h’F). The Pearson correlation analysis highlights the rapid coupling between interplanetary magnetic field (IMF) and local equatorial magnetic fields during geomagnetic storms. These observations enhance our understanding of geomagnetic storm impacts in equatorial regions, which is crucial for improving space weather forecasting and mitigation strategies, especially for GNSS-dependent systems and radio communications.
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Corrigendum to “Spatio-temporal characteristics of ionospheric irregularities in low latitude regions during the peak of solar cycle 25” [Adv. Space Res. 76(1) (2025) 254–268, (S0273117725004168), (10.1016/j.asr.2025.04.062)]
(2025-09-01)
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
The authors regret that the following was omitted from the acknowledgment section: This research project is also financially supported by National Research Council of Thailand (NRCT) under grant N41A640235. The authors would like to apologise for any inconvenience caused.
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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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Impact of ionospheric disturbances on NIC and NACp degradation in ADS-B messages
(2025-01-01)
Takahashi, Toru
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Pongpeaw, Anurak
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Saito, Susumu
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Koga, Tadashi
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Supnithi, Pornchai
Southern Japan is located in the low geomagnetic latitude region, where amplitude scintillations associated with equatorial plasma bubbles are often observed. The Electronic Navigation Research Institute (ENRI) has installed GNSS scintillation receivers and an all-sky camera on Ishigaki Island to monitor ionospheric disturbances. The GNSS receivers used are Septentrio Pola5S, which are also utilized for the Ground Based Augmentation System (GBAS) at New Ishigaki Airport (24.4 deg. N, 124.2 deg. E), which is the southernmost airport with regular flights in Japan. The all-sky camera can capture ionospheric disturbances, such as plasma bubbles. The ADS-B receiver has also been installed at Ishigaki Island and received its message within almost 150 NM. The ADS-B observation on Ishigaki Island has been operational since 2023. We observed that plasma bubbles and degradations in NIC and NACp values occurred simultaneously on March 16, 2024. We calculated the Ionospheric Pierce Points (IPP) of GPS satellites observed by aircraft showing degraded NIC and NACp values. Plasma bubbles captured by the all-sky camera were projected onto the map. One GPS satellite's IPP from the flight, which sent those degraded values, was located at the edge of a plasma bubble, and the potential impact of the plasma bubble was considered. However, same analyses were conducted on two other satellites flying in the vicinity, and although these two flights were in conditions that were either equivalent to or more susceptible to the effects of the plasma bubble, neither the NIC nor NACp showed any degradation. Therefore, Instead, radio frequency interference (RFI), or equipment failure is likely one of the causes of these degradations.
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Statistical analysis and effects of radio frequency interference in GPS signal quality in Thailand
(2024-10-01)
Sophan, Somkit
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Supnithi, Pornchai
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Myint, Lin M.M.
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Budtho, Jirapoom
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Saito, Susumu
The radio frequency interference (RFI) in global navigation satellite system (GNSS) signals has recently received much attention in the GNSS community because of frequent jamming issues. The carrier-to-noise density ratio (C/N<inf>0</inf>) is one of the common parameters to indicate the signal quality. In this work, we propose a real-time RFI analysis based on windowing and normalization of C/N<inf>0</inf> observations. Specifically, the percentage of RFI values are analyzed based on the modified RFI detection. The steps to analyze the RFI levels (low, medium, high) are highlighted. In addition, we analyzed the occurrences of local RFI effects in areas surrounding the Suvarnabhumi International Airport as well as remote areas. We validate the modified RFI detection by using the GNSS reference stations at the urban, suburban, and outside the capital city in Thailand. The user positioning errors with the high (severe) RFI levels are investigated based on the single point positioning (SPP) and real-time kinematics (RTK). From the experimental simulations, the high RFI levels at the urban are higher than those at the suburban. As expected, the statistical analysis covering COVID-19 (2019 to 2023) shows that the high RFI levels in June 2023 (post COVID-19) are more than those in June 2020 and 2021 (lockdown COVID-19) by about twofold. Additionally, the SPP positioning errors with the medium/high RFI levels are clearly seen. There are more floating solutions in the RTK system in the year with more RFI presence.
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Local mitigation of higher-order ionospheric effects in DFMC SBAS and system performance evaluation
(2024-04-01)
Sophan, Somkit
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Supnithi, Pornchai
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Myint, Lin M.M.
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Saito, Susumu
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Hozumi, Kornyanat
Dual-frequency multi-constellation (DFMC) satellite-based augmentation system (SBAS) is a new SBAS standard for aeronautical navigation systems. It supports aircraft navigation from the enroute to approach phases via the L1 and L5 frequencies (1575.42 and 1176.45 MHz). Although the ionosphere-free (IF) combination in the DFMC SBAS operation removes the first-order ionospheric delays in the pseudorange measurement, remaining terms including the satellite-clock offset errors and higher-order ionospheric (HOI) delays are still unaccounted for. The DFMC SBAS accuracy and integrity can be affected by the HOI effects, especially during severe ionospheric disturbances. In this work, we present the local DFMC SBAS corrections with and without the mitigation of HOI delays. We first estimate the HOI delay terms using the received pseudorange followed by separate satellite and receiver bias estimations based on the minimum sum-variance technique. The integrity terms can then be obtained. The performances of DFMC SBAS using the global navigation satellite system (GNSS) data including GPS, Galileo, and QZSS are evaluated using obtained GNSS data at stations in Thailand on the ionospheric quiet and disturbed days. The results show that with the HOI mitigation, the vertical positioning errors (VPE) on the quiet and disturbed days can be improved by 12% and 9%, whereas the vertical protection levels (VPL) are improved by 16% and 21%, respectively. In addition, we perform a preliminary assessment of DFMC SBAS based on the International Civil Aviation Organization (ICAO) requirements of two categories: Localizer Performance with Vertical guidance (LPV-200) and Category I precision approach (CAT-I) showing promising results.
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Ground Facility Error Analysis and GBAS Performance Evaluation Around Suvarnabhumi Airport, Thailand
(2024-02-01)
Budtho, Jirapoom
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Supnithi, Pornchai
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Siansawasdi, Nattapong
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Saito, Susumu
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Saekow, Apitep
The performances of the ground-based augmentation system (GBAS) designed for the landing phase of aircraft rely on the accurate characterization of error models. Among various error sources, the multipath model, which is typically constructed by combining environmental errors at airports, must be modeled in GBAS. However, in practice, the multipath effects at a particular airport differ from other airports due to distinct construction sites and continually changing environments, resulting in an inaccurate error model in GBAS operations. Therefore, in this article, we develop and evaluate a 2-D ground facility error model from the Global Navigation Satellite System Stations (GNSS) at the Suvarnabhumi International Airport in Bangkok, Thailand. The results indicate that the elevation and azimuth grid points require around seven days of observation data to create the GBAS ground facility error model for GBAS operation. The number of observations per day at each elevation and azimuth grid point will determine the data requirements for the complete building of the 2-D ground error model. When the proposed model is applied to the GBAS simulation, it is found that the proposed 2-D ground error model reduces the root-mean-square deviation (RMSD) of positioning errors by around 0.4% to 3.5% when compared to the 1-D error model and the category B Ground accuracy designator model, respectively. The maximum vertical protection level reduction of the proposed 2-D B-value model in comparison with the reference 1-D B-value is 0.24 m, about a 6% reduction.
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Radio Frequency Interference (RFI) Analysis on GNSS Signals and Effects on Positioning Errors
(2024-01-01)
Sophan, Somkit
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Supnithi, Pornchai
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Myint, Lin M.M.
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Budtho, Jirapoom
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Saito, Susumu
Radio frequency interference (RFI) frequently exists in the Global Navigation Satellite System (GNSS) signals. Conventionally, the monitoring of carrier-to-noise density ratio (C/N0) values can be used to detect the RFI levels. Since RFI affects the quality of GNSS signals and applications, we determine three RFI levels (low, moderate, and high) based on C/N0 then statistically analyze the RFI occurrences in Bangkok, Thailand. The percentage of RFI occurrences is computed based on the average C/N0 technique. We compare the RFI occurrence statistics of 2 GNSS stations in the urban (DPT9) and suburban (KMIT) areas in Bangkok in June 2021 (COVID-19 lockdown period) and 2023 (Post COVID-19 period). The results show that during the COVID-19 period, the RFI occurrences are much reduced at the DPT9 station in the center of the city. The high (severe) RFI levels at DPT9 (urban) are mostly higher than those at KMIT station (suburban). In addition, we investigate the effects of high (severe) RFI events on single-point and real-time kinematics (RTK) positioning errors.
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Ionospheric Scintillation Prediction Using Decision Tree and Rainforest Techniques
(2024-01-01)
Trachuentong, Sirasake
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Supnithi, Pornchai
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Myint, Lin Min Min
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Saito, Susumu
The ionosphere contains electron density variation. When radio signals transmitted from global navigation satellite systems (GNSS) pass through such medium, additional delays are added. With ionospheric irregularity, fluctuation in GNSS signals known as scintillation are often observed resulting in reduced number of tracked satellites then degrade positioning performances. At present, scintillation is considered random, hence, the ability to detect or predict such phenomenon is crucial to efficient system operation. In this research, we design machine learning algorithm for scintillation prediction. Both Decision Tree (DT) and Random Decision Forest (RF), are implemented to predict daily ionospheric scintillation at King Mongkut's Institute of Technology Ladkrabang (KMITL) station in Thailand (13.73 ° E, 100.77° N). The rate of total electron content change index (ROTI) is also used. Modeling is carried out for four months in March (equinox), June (solstice), September (equinox), and December (solstice) in 2022, representing different seasons in space weather study. The prediction results are evaluated using the S 4 index observations at KMITL station and then compared between DT and RF methods. The designed model has a high potential for scintillation prediction.
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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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