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Author: search.filters.author.Kenpankho, P.Start date: 2020

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    Ionospheric disturbances as precursor signals of the March 28, 2025, Myanmar earthquake
    (2026-03-15)
    Pansong, C.
    ;
    Ruttanaburee, S.
    ;
    Pornsopin, P.
    ;
    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 TEC disturbances during extreme geomagnetic storms: insights into March and May 2024
    (2025-12-15)
    Pansong, C.
    ;
    Wongsak, P.
    ;
    Ruttanaburee, S.
    ;
    Pornsopin, P.
    ;
    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.