KMITL

Permanent URI for this communityhttps://dspace.kmitl.ac.th/handle/123456789/1

Browse

Search Results

Now showing 1 - 7 of 7

Some of the metrics are blocked by your
consent settings
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.
Some of the metrics are blocked by your
consent settings
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<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.
Some of the metrics are blocked by your
consent settings
The investigation on daytime conjugate hemispheric asymmetry along 100°E longitude using observations and model simulations: New insights
(2022-05-15)
Kalita, B. R.
;
Bhuyan, P. K.
;
Nath, S. J.
;
Choudhury, M. C.
;
Chakrabarty, D.
The hemispherical asymmetry of the low latitude region along 100°E ± 5°E is scrutinized for the year 2015 at magnetically conjugate points on seasonal and intra-seasonal time scales. Two conjugate Ionosonde station pairs are selected- one pair in the inner valley (from SEALION) and the other in the outer edges of the EIA region. The anomaly in the stations is estimated using the difference of low latitude NmF2 from the dip equatorial NmF2 in the same meridian. A monthly average scheme is used instead of a seasonal mean, as the month-to-month variations are found to provide intricate details. The anomaly at the conjugate stations is highly asymmetric even during the equinoctial months of March and October, whereas it is nearly symmetric during April. During June/July, the morning time hemispheric asymmetry (larger on the winter side) temporarily reduces in the midday period and then reverses sign (larger in summer) in the afternoon. The NmF2 observations suggest a close relation of hemispheric symmetry to the position of the subsolar point with respect to the dip equator and a shift/expansion of the trough region of the EIA towards the summer hemisphere. The inter-hemispheric comparison of the hmF2 suggests a strong modulating influence of meridional winds at both the inner and outer stations which depend strongly on the relative position of the subsolar point with respect to the field line geometry. Theoretical (SAMI3/SAMI2) and empirical model (IRI) simulations show a meridional movement of the EIA region with the subsolar point. The winter to summer hemisphere movement of the EIA trough and crest region is also reproduced in the GIM-TEC along 100°E for 2015. This shifting or tailoring of the trough and the crest region is attributed primarily to the meridional wind field, which varies with the shifting position of subsolar point relative to the field line geometry. The seasonal and intra-seasonal difference in the NmF2 hemispheric asymmetry is attributed to the misalignment of the two centers of power viz., the thermospheric/neutral processes and the electromagnetic forces, due to the geographic-geomagnetic offset in this longitude.
Some of the metrics are blocked by your
consent settings
Ionospheric peak height at the magnetic equator: Comparison between ionosonde measurements and IRI
(2017-07-15)
Maruyama, Takashi
;
Ma, Guanyi
;
Tsugawa, Takuya
;
Supnithi, Pornchai
;
Komolmis, Tharadol
The ionospheric peak height in the F layer (hmF2) varies with not only thermospheric conditions but also dynamic processes in the upper atmosphere. At mid-latitudes, the field-aligned diffusion and recombination loss determine the hmF2 in the absence of applied vertical drift. Vertical drifts displace the hmF2 to a new equilibrium position in conjunction with the field-aligned redistribution of the plasma. In the vicinity of the magnetic equator, however, the equilibrium state would be different from low and mid-latitudes because the direct vertical coupling of plasma through the diffusion process is not allowed. Thus the behavior of hmF2 cannot be simply an extrapolation of that at low latitudes. In this paper, ionosonde measurements of the hmF2 near the magnetic equator and off-equatorial latitudes are compared with the IRI output.
Some of the metrics are blocked by your
consent settings
Comparison of ionosphere characteristic parameters obtained by ionosonde with IRI-2007 model over Southeast Asia
(2013-11-15)
Wichaipanich, N.
;
Supnithi, P.
;
Tsugawa, T.
;
Maruyama, T.
;
Nagatsuma, T.
In this work, the foF2 and hmF2 parameters at the conjugate points near the magnetic equator of Southeast Asia are studied and compared with the International Reference Ionosphere (IRI) model. Three ionosondes are installed nearly along the magnetic meridian of 100 E; one at the magnetic equator, namely Chumphon (10.72 N, 99.37 E, dip angle 3.0 N), and the other two at the magnetic conjugate points, namely Chiang Mai (18.76 N, 98.93 E, dip angle 12.7 N) and Kototabang (0.2 S, 100.30 E, dip angle 10.1 S). The monthly hourly medians of the foF2 and hmF2 parameters are calculated and compared with the predictions obtained from the IRI-2007 model from January 2004 to February 2007. Our results show that: the variations of foF2 and hmF2 predicted by the IRI-2007 model generally show the similar feature to the observed data. Both parameters generally show better agreement with the IRI predictions during daytime than during nighttime. For foF2, most of the results show that the IRI model overestimates the observed foF2 at the magnetic equator (Chumphon), underestimates at the northern crest (Chiang Mai) and is close to the measured ones at the southern crest of the EIA (Kototabang). For hmF2, the predicted hmF2 values are close to the hmF2(M3000F2 <inf>OBS</inf> ) during daytime. During nighttime, the IRI model gives the underestimation at the magnetic equator and the overestimation at both EIA crests. The results are important for the future improvements of the IRI model for foF2 and hmF2 over Southeast Asia region. © 2012 COSPAR. Published by Elsevier Ltd. All rights reserved.
Some of the metrics are blocked by your
consent settings
Ionospheric variation at Thailand equatorial latitude station: Comparison between observations and IRI-2001 model predictions
(2010-01-15)
Wichaipanich, Noraset
;
Supnithi, Pornchai
;
Ishii, Mamoru
;
Maruyama, Takashi
In this paper, the F2-layer critical frequency (foF2) and peak height (hmF2) measured by the FM/CW ionosonde at Thailand equatorial latitude station, namely Chumphon (10.72°N, 99.37°E, dip 3.22) are presented. The measurement data during low solar activity from January 2004 to December 2006 are analyzed based on the diurnal, seasonal variation. The results are then compared with IRI-2001 model predictions. Our study shows that: (1) In general, both the URSI and CCIR options of the IRI model give foF2 close to the measured ones, but the CCIR option produces a smaller range of deviation than the URSI option. The agreement during daytime is generally better than during nighttime. Overestimation mostly occurs in 2004 and 2006, while underestimation is during pre-sunrise hours in June solstice in 2005. The peak foF2 around sunset is higher during March equinox and September equinox than the other seasons, with longer duration of maximum levels in March equinox than September equinox. Large coefficients of variability foF2 occur during pre-sunrise hours. Meanwhile, the best agreement between the observed foF2 and the IRI model is obtained in June solstice. (2) In general, The IRI (CCIR) model predicts the observed hmF2 well during daytime in June solstice from 2004-2006, but it overestimates during March equinox, September equinox and December solstice. For nighttime, the model overestimates hmF2 values for all seasons especially during March equinox and September equinox. However, the model underestimates hmF2 values during September equinox and for some cases during June solstice and December solstice at pre-sunrise. The agreement between the IRI model and the hmF2(M3000 <inf>OBS</inf> ) is worst around noontime, post-sunset and pre-sunrise hours. All comparative studies give feedback for new improvements of CCIR and URSI IRI models. © 2009.
Some of the metrics are blocked by your
consent settings
Thailand equatorial F2-layer peak height and comparison with the IRI-2001 model
(2009-12-01)
Wichaipanich, Noraset
;
Supnithi, Pornchai
In this paper, the F2-layer peak height (hmF2) are calculated from the observed M(3000)F2 and then compared with IRI-2001 model. The data used for this study are obtained from bottomside ionogram recorded by the FM/CW ionosonde at Chumphon campus of King Mongkut's institute of Technology Ladkrabang (latitude 10.72°N and longitude 99.37°E), Thailand, located near the magnetic equator. The measurement data including March, June, September and December in 2004, 2005 and 2006 for the period of low solar activity, are analyzed and then compared with IRI-2001 model predictions. Our study shows that the agreement between the data and the model at Southeast Asia will be better if the Shimazaki's formula is used. The results are important for the future improvements of the IRI model for the hmF2 at Thailand equatorial latitude. ©2009 IEEE.

KMITL

Browse

Filters

Settings

Sort By

Results per page

Search Results