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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
;
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–1) 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–1) 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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Complex Ionospheric Irregularity Echoes Observed by Low Latitude Long Range Ionospheric Radar
(2026-01-01)
Li, Yuxiao
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Hu, Lianhuan
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Li, Guozhu
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Ning, Baiqi
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Dai, Guofeng
Using the Low lAtitude long Range Ionospheric raDar (LARID) at Dongfang (19.2°N, 108.8°E), Hainan Island, China, we report a unique case of complex ionospheric irregularities observed on 9 June 2024. The most interesting aspect is the first-time long-range (∼2,000 km) detection of daytime ionospheric irregularities and post-sunset band-like irregularity structures by HF radar at low latitudes. By incorporating VHF radar and global navigation satellite system (GNSS) rate of total electron content index (ROTI) observations, the radio wave propagation modes of the ionospheric irregularity events observed by LARID and evolution of these ionospheric irregularities were analyzed. The daytime ionospheric irregularity echoes observed by LARID over the Indian Ocean exhibited westward drift, evident in both echo patterns and Doppler velocities. These ionospheric echoes were likely backscattered from E region field aligned irregularities by the “downleg” of the 1-hop HF ray path. The post-sunset irregularity echoes observed by LARID over Indian Ocean manifested as a band-like structure. This structure was closely attached to the bottom of ground/sea scatter echoes and showed the same range variation as the ground/sea scatters. GNSS ROTI observation revealed that irregularities primarily appeared south of the magnetic equator and drifted eastward across the eastern longitudes in later hours. Analysis indicates that the displacement of small-scale irregularities within the equatorial plasma bubble event along the magnetic field likely contributed to the band-like irregularity structure observed by LARID and the asymmetric irregularity distribution observed by GNSS.
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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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Study on the relationship between Global Positioning System Total Electron Content Anomalies and Earthquake Events in Thailand during Solar Cycle 24
(2025-10-29)
Pansong, Chollada
;
Kenpankho, Prasert
This study investigates ionospheric Total Electron Content (TEC) anomalies in relation to earthquake events in Thailand from 2007 to 2020, encompassing Solar Cycle 24. TEC data were obtained from three sources: the Global Positioning System (GPS), the International GNSS Service (IGS), and the International Reference Ionosphere (IRI), and were compared to 473 earthquakes (Mw ≥ 3.0). While earthquake magnitudes below Mw 5.0 did not exhibit a clear correlation, earthquake events of Mw 5.0 or higher reflected in moderate negative correlation coefficients for GPS TEC, IGS TEC, and IRI TEC (-0.495,-0.501, and-0.303, respectively). Furthermore, a positive correlation coefficient (0.611) was found between Mw ≥ 5.0 earthquakes and geomagnetic storms with the Kp index. However, focusing specifically on geomagnetic storms and TEC variations on the day of an earthquake, no significant relationship was detected across GPS, IGS, and IRI data. Nevertheless, further research is needed to clarify the link between seismic activity and TEC fluctuations, potentially through alternative approaches or targeted case studies. This is especially important given the limited number of earthquakes above a magnitude of 5.0 in our study area, which restricts the available sample size.
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The study of total electron content on ionosphere by using single frequency GPS receiver
(2025-03-01)
Keokhumcheng, Thanapon
;
Kenpankho, Prasert
In this research, we studied total electron content (TEC) on ionosphere by using single frequency from global positioning satellite system (GPS) satellite receiver. According to the ionospheric disturbance, ionospheric delay time on TEC is one of the most significant errors in GPS navigation systems. The positioning errors for GPS satellite systems from ionospheric delay depends on TEC over the region of interest as low latitude, Thailand. In research methodology, we proposed our ionospheric delay dataset on the period of the year 2004–2023 into the single frequency TEC method for finding GPS TEC. We investigated single frequency GPS TEC in three different stations, Bangkok, Chiang Mai, and Chumphon. Each station was installed the single and dual frequency GPS receivers for receiving the GPS signals over Thailand region. We investigated and compared single frequency GPS TEC results with dual frequency GPS TEC, International GNSS Service TEC (IGS TEC), and International Reference Ionosphere TEC (IRI TEC) in the year 2023. As the results, TEC using the single frequency GPS receiver is significantly statistical to be use for the study TEC on ionosphere over low latitude, Thailand.
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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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A Novel Short-Term Prediction Model for Regional Equatorial Plasma Bubble Irregularities in East and Southeast Asia
(2025-02-01)
Zhao, Xiukuan
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Li, Guozhu
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Xie, Haiyong
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Hu, Lianhuan
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Sun, Wenjie
Equatorial plasma bubble (EPB) irregularities can significantly impact satellite-based communication and navigation systems. Accurate prediction of EPB occurrence is essential for mitigating these impacts. Using the GNSS receiver network and ionosonde data from East and Southeast Asia during 2010–2021, and the rate of TEC change index to characterize the occurrence of EPB irregularities, we developed a novel Spatio-Temporal deep learning model for regional EPB irregularities short-term Prediction (STEP). The model integrates the convolutional neural network and long short-term memory (LSTM) network, together with attention mechanisms, to capture both spatial and temporal features of regional ionospheric irregularities. The results show that for 5-min forecast, the STEP model achieves a root mean square error (RMSE) of 0.062 TECU/min and an R2 of 0.818, reducing RMSE by 19.48% compared to LSTM and 27.06% compared to gated recurrent unit model. For 60-min prediction, the STEP model can still achieve reasonable accuracy with an RMSE of 0.110 TECU/min and an R2 of 0.482, showing significant improvement over traditional models. The equatorial F layer height and regional TEC fluctuations were identified as the most critical factors for predicting the generation and duration of EPB irregularities, respectively. The spatial and temporal distributions of EPB irregularities, including their latitudinal variation and delayed onset after sunset, and the occurrence across different days in East and Southeast Asia, were well predicted by the STEP. It is expected that the STEP model would provide a valuable tool for improving the resilience of GNSS against ionospheric scintillations induced by EPB irregularities.
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Exploring Ionospheric Disturbances Using GNSS: A STEM-Based Investigation of the 2024 Extreme Geomagnetic Storm
(2025-01-01)
Pansong, Chollada
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Buakao, Nitipat
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Keokhumcheng, Thanapon
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Phothila, Pharinya
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Intamas, Patcharin
This study investigates the effectiveness of a STEM-based instructional approach integrating GNSS satellite technology and ionospheric TEC (Total Electron Content) analysis during extreme geomagnetic storms. The objective was to enhance students' conceptual understanding, practical skills, and STEM-related attitudes through interdisciplinary learning activities. The SPACE model (Study, Plan, Analyze, Create, Evaluate) was applied as a pedagogical framework to guide students through real-world TEC anomaly detection using GPS RINEX data and computational tools. The integration of real satellite data and hands-on analysis enabled students to connect theoretical knowledge with real-world phenomena, deepening their engagement and inquiry-based thinking. Pre-and post-test results revealed statistically significant improvements, with scores increasing from a mean of 5 1. 8 (S D = 7. 5 4) to 7 5. 0(S D= 7.42) (p < 0. 000001). Moreover, the STEM Attitude Questionnaire reflected strong positive perceptions, especially in STEM career motivation (x¯=4.20) and perceived value of STEM (x¯= 4.13). These findings highlight the model's potential to foster STEM readiness. Integrating GNSS-based TEC analysis into the STEM framework significantly enhanced students' academic outcomes, practical skills, and STEM attitudes.
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Global Navigation Satellite System (GNSS) Low-Cost Robotics Platform for Competition Game
(2025-01-01)
Sumniang, Patiphan
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Putthong, Burin
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Namniwong, Thapanan
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Kenpankho, Prasert
In this research, the Global Navigation Satellite System (GNSS) low-cost robotics platform for competition game was designed, including the development of competition rules and field. The competition rules are specifically tailored to GNSS low-cost robot, highlighting the essential components required to build robots based on GNSS low-cost robotic platform. This research aims to promote learning and skill development in robots and GNSS, with a focus on affordable resources to ensure accessibility for students and independent developers. In research methodology, a total of 58 teams with 116 participants took part in the GNSS low-cost robotics platform competition game, including 47 high school level teams (94 participants), 6 vocational level teams (12 participants), and five undergraduate level teams (1 0 participants). As the results, the competition game was successfully developed by the GNSS low-cost robotic platform, with over 70% of participants demonstrating a solid understanding of GNSS navigation, robot, and game design. Participants rated innovation-focused activities highly (4.55), highlighting the competition game role in inspiring creativity in GNSS and low-cost robot. In term of rule for competition game, participants gave the rates on fairness (4.23) and consistency (4.28) which were well received, although rule clarity received the lowest score (3.84), suggesting the need for clearer guidelines. In addition, the pre- and posttest assessments on participants' knowledge, understanding, and inspiration in GNSS navigation, robot, and game design, further confirmed the effectiveness of GNSS low-cost robotics platform competition game by giving the improved mean score from 23.06 to 27.01.
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Study of Ionospheric Total Electron Content over Thailand Using BeiDou Satellites
(2025-01-01)
Maichuen, Samatchaya
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Keokhumcheng, Thanapon
;
Kenpankho, Prasert
This study aims to analyze the Total Electron Content (TEC) in the ionosphere over Thailand using BeiDou satellite signals received by BG2s receivers, providing an alternative to the traditional use of GPS satellites for investigating TEC variations. Data were collected from January to March 2025 from six monitoring stations: Bangkok, Chiang Mai, Chumphon, Nong Bua Lam Phu, Phuket, and Ubon Ratchathani, respectively, covering the entire region of Thailand. The analysis revealed that Nong Bua Lamphu recorded the highest average at 77.94 TECU, followed by Chiang Mai with 73.55 TECU. Ubon Ratchathani had an average of 65.81 TECU, while Phuket recorded 59.54 TECU, closely followed by Bangkok with 59.22 TECU. Chumphon had the lowest average maximum value at 45.00 TECU, respectively. Additionally, training sessions were conducted for 20 participants of the Meteorological Department on using BG2s receivers to measure TEC from BeiDou satellites. The pre-training assessment showed that 6 participants, accounting for 30%, achieved scores above 80%. After the training, all participants, representing 100%, surpassed the 80% threshold. The results indicate an improvement in participants' knowledge from 30% to 100%, reflecting the success of the training program and demonstrating the potential for applying the BeiDou satellite system in future ionospheric TEC studies.

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