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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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On the variations in equatorial and low-latitude GPS-TEC and assessment of NeQuick-2, IRI-2016 and IRI-2020 models in the African longitude during solar cycle 24–25
(2025-03-01)
Ogwala, Aghogho
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Akinbuli, Feyisara Fehintoluwa
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Panda, Sampad Kumar
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Jamjareegulgarn, Punyawi
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Siddiqui, Md Irfanul Haque
Ionospheric models play a crucial role in understanding, prediction, and mitigation of the effects of ionospheric variability on a wide range of technological and scientific applications relying on space-based services. Conversely, the models need to be routinely updated with newer datasets and specifications to account for the regional discrepancies in the changing ionospheric conditions due to various dominant localized physical and chemical processes. Although there have been ongoing improvements to the extensively utilized empirical model known as the International Reference Ionosphere (IRI), the newly emerged version (IRI-2020) needs to undergo global testing. In this research, we carried out diurnal and seasonal variations in GPS-TEC and the assessment of some ionospheric models such as IRI-2016 and its recently updated version (IRI-2020), alongside the NeQuick-2 model at 2 stations each in the East, West and South in the equatorial and low-latitude African longitudes during different phases of solar cycles 24–25 (2016 – 2021). Also, we carried out statistical analysis between GPS-TEC and the ionospheric models using Root Mean Square Error (RMSE) and Mean Absolute Error (MAE), in order to show the model with the best forecasting capability in the African region. Diurnal, seasonal and solar cycle variations in GPS-TEC, NeQuick-2, IRI-2016 and IRI-2020 were observed, showing higher magnitudes in the West, followed by the East in close range and least in the Southern sector of the African longitudes. TEC Variations in some sectors in the African longitudes show a consistent trend in this research. More importantly, there are observed regional differences within the African longitudes owing to the wider coverage of landmass in the equatorial and low latitudes. However, TEC variations in the Northern sector of Africa are not included in the present research. From our observation, NeQuick-2 and IRI-2016 models either underestimate or overestimate GPS-TEC during different phases of the solar cycles at the three sectors in the African longitudes, whereas IRI-2020 shows mostly underestimating characteristics at the three sectors irrespective of solar activity conditions during the study period. Nevertheless, the underestimation or overestimation of NeQuick-2 and IRI-2016, and the underestimation of IRI-2020 are reflected in the RMSE and MAE values. Regrettably, the predictions from IRI-2020 model are not satisfactory at any of the three sectors in the African longitudes and prompt attention of the modeling community for further investigations towards possible refinements in the model specifications.
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Longitudinal Variations in Equatorial Ionospheric TEC from GPS, Global Ionosphere Map and International Reference Ionosphere-2016 during the Descending and Minimum Phases of Solar Cycle 24
(2022-11-01)
Ogwala, Aghogho
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Oyedokun, Oluwole Johnson
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Ogunmodimu, Olugbenga
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Akala, Andrew Ovie
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Ali, Masood Ashraf
Research on longitudinal discrepancies in local ionospheric variability, especially in equatorial and low-latitude regions, is a focal point of interest for the space weather modeling community. The ionosphere over these regions is influenced by complex electrodynamics, wind, and temperature dynamics that can seriously impact dynamic technological systems such as satellite tracking and positioning, satellite radio communication, and navigation control systems. Here, we researched the longitudinal variability in the ionospheric total electron content (TEC) by analyzing observed global positioning system (GPS)-derived TEC values along with those extracted from the most reliable global ionospheric maps (GIMs) and the International Reference Ionosphere (IRI-2016) model at selected stations in the vicinity of the magnetic equator along the American, African, and Asian longitude sectors. The period of study covered the descending (2016–2017) and deep solar minimum (2018–2019) years in the 24th solar cycle. Apart from the decreasing trend of the TEC from the descending to deep solar minimum period irrespective of season and longitude sector, the results showed a relatively higher magnitude of TEC in the African longitude than the other two longitude sectors. Despite evident overestimation and underestimations of TEC in both models, GIM predictions generally looked better in terms of observed variation patterns, especially in the African longitude. The study also highlights the seasonal and semiannual effects of longitudinal variations in TEC, manifesting in local time offsets and some peculiar anomalies, which seemed to be different from previously reported results, especially during the solar minimum years at the three longitude sectors. The insignificant effects of longitudinal variations on the equinoctial asymmetry are attributed to the diverse electron density distribution and ionospheric morphology at the three longitude sectors that will prompt further investigations in the future. The outcomes from this study may augment the past efforts of scientists to understand the seasonal effects of the longitudinal variations in TEC, thereby complementing the improvements of ionospheric representations in global ionosphere models and maps.
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Individual performance of multi-GNSS signals in the determination of STEC over Thailand with the applicability of Klobuchar model
(2022-02-01)
Seok, Hong Woo
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Ansari, Kutubuddin
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Panachai, Chaiwat
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Jamjareegulgarn, Punyawi
Thailand is situated in the southern low latitude region in the Asian longitude sector having much importance as major portion of southern hemisphere is covered by ocean resulting in a sparse density of ground-based monitoring systems. With the establishment of GNSS monitoring stations across the Thailand and neighboring region, it accentuates the ionospheric variability study in the southern hemisphere in the Asian longitude. Therefore, in the current study, we selected four GNSS station located at different part of the country (i.e., CHMA, DPT9, NKRM, and SRTN) and studied the variations of ionospheric slant total electron content (STEC). Here, the STEC observations are estimated by Klobuchar model (namely, Klobuchar-modeled STEC values) and compared with the Global Ionospheric Map (GIM) STEC values for its validation. As an initial study, the Klobuchar-modeled STEC values obtained from five multi-constellation GNSSs over Thailand region (i.e., GPS, GLONASS, Galileo, BeiDou and QZSS) are computed and compared with the GIM STEC values during the intense geomagnetic storm on May 12, 2021 (DOY 132) and during June 2020 to May 2021 for monthly variations. Moreover, to show the relationships between the proposed Klobuchar-modeled STEC values and the GIM STEC values, the correlation coefficients and the root mean square errors between them are computed. The results showed that among the five multi-constellations of GNSSs, the GIM STEC values frequently overestimate the Klobuchar-modeled STEC values, except the QZSS system with the least differences ranging from −10 TECU to 20 TECU. Also, the correlation coefficient between the proposed Klobuchar-modeled and GIM STEC variations span between 0.87 and 0.89, and their RMSEs range from 10 TECU to 11 TECU, excluding QZSS system with less than 10 TECU. The correlation coefficients of higher than 0.85 can be considered as a good indicator for the applicability of Klobuchar model in practice with multi constellation systems.
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Singular spectrum analysis of GPS derived ionospheric TEC variations over Nepal during the low solar activity period
(2020-04-01)
Ansari, Kutubuddin
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Panda, Sampad Kumar
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Jamjareegulgarn, Punyawi
Accurate modeling of ionospheric total electron content (TEC) is an important aspect for mitigating the threats of trans-ionospheric delay error in satellite communication, earth observation, space-based navigation, timing applications as well as space weather forecasting services. In recent years, singular spectrum analysis (SSA) has been proved to be a powerful technique giving a relatively accurate estimate in time-series analysis comparable to the contemporary methods. In the current study, the SSA has been implemented on the GPS-derived TEC during the low solar activity year of 2017 over Nepal region which locates itself almost in the vicinity of low-latitudes being sandwiched between India and Tibet, China. The country foresees an explicit investigation and modeling of ionospheric TEC variations and corresponding delay error to precisely accomplish the space-based trans-ionospheric applications. The semi-annual variability of TEC with higher magnitudes during equinoctial seasons and lower values during solstice seasons is clearly noticed in the diurnal plots which are further substantiated by the trajectory matrix of time-series. The decomposed modes in the principal component analysis (PCA) signifies diurnal (first), semidiurnal (second), semiannual (third), monthly (fourth) with higher orders representing associated noise errors in the signals. Correlation coefficients (CC) between the reconstructed and observed time-series demonstrates the SSA method could be a successful tool for forecasting the TEC series over the region. The results are compared with empirical global ionospheric maps (GIMs) and IRI-Plas 2017 models during different seasons, emphasizing the suitability of SSA technique for relatively better precise TEC forecasting over the region.
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Analysis of Bottomside Thickness Parameter-Based TEC at Equatorial and Low Latitude Stations for Global Navigation Satellite Systems
(2018-07-02)
Jamjareegulgarn, Punyawi
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Duangsuwan, Sarun
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Tangtrakunphaisan, Udomsit
This paper studies the total electron content (TEC) at equatorial and low latitude stations which is computed using an equation of bottomside thickness parameter with correction factor (B2botP-new) during the solar maximum of 24th solar cycle. The computed TEC is used to compute the ionospheric time delay subsequent-tially. The ionospheric stations in this work include Ramey, Ascension Island, and Jicamarca. The results show that the diurnal and seasonal variations of B2botP-new have the same trends as that of B0-obs as well as the B2botP-new values are close to the BO-obs values clearly for all three stations. The electron density diffuses from the equator toward the EIA region (15°N and 15°S) during the period of 14-23 LT. The proposed TEC (TEC-P) are computed using the B2botP-new, and then the ionospheric delay is also computed using the TEC-P. The computed TEC-P and Id-P are close to the TEC-obs and Id-obs, but they should be further studied for a solar cycle (11 years).
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A correction factor of bottomside thickness parameter for computing TEC in global navigation satellite systems
(2017-10-19)
Jamjareegulgarn, Punyawi
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Supnithi, Pornchai
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Hozumi, Kornyanat
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Tsugawa, Takuya
This paper proposes two new equations for computing the bottomside thickness parameter of the NeQuick 2 model with a correction factor (B2bot Pro2) and the simulated TEC values (TEC Pro). The main contributions of this work are twofold, i.e., 1) the proposed B2bot Pro2 equation can be used to compute the bottomside thickness whose trends and values are close to ones of the observed B0 (B0 obs) obtains from DPS-4 (Digisonde) and 2) the computed B2bot Pro2 are used to compute the TEC values without additional TEC observation by any devices and TEC computation. In this case, it is useful for some locations where there exist only ground-based ionosonde without TEC observation or TEC measurement doesn't work in some situations. The results show that the B2bot Pro2 have the same trends as the B0 obs. They are closer to the B0 obs, except at 13LT in June solstice and September equinox. The averages of absolute differences between B2bot Pro2 and B0 obs (avAD Pro2) are generally lower than about 8 km. They show that the B2bot Pro2 are close to the B0 obs with the improved percentages of higher than 80%. The TEC computed using the B2bot Pro2 equation (TEC Pro) in the nighttime are generally close to the observed TEC (TEC obs) compared with those in the daytime.

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