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Monitoring of equatorial plasma bubbles using aeronautical navigation system: a feasibility study
(2023-12-01)
Hosokawa, Keisuke
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Saito, Susumu
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Nakata, Hiroyuki
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Lin, Chien Hung
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Lin, Jia Ting
It has long been known that field-aligned irregularities within equatorial plasma bubbles (EPBs) can cause long-range propagation of radio waves in the VHF frequencies such as those used for TV broadcasting through the so-called forward scattering process. However, no attempt has been made to use such anomalous propagations of VHF radio waves for wide-area monitoring of EPBs. In this study, we investigated the feasibility of monitoring of EPBs using VHF radio waves used for aeronautical navigation systems such as VHF Omnidirectional radio Range (VOR). There are 370 VOR stations in the Eastern and Southeastern Asian region that can be potentially used as Tx stations for the observations of anomalous propagation. We have examined the forward scattering conditions of VHF waves using the magnetic field model and confirmed that it is possible to observe the EPB-related anomalous propagation if we set up Rx stations in Okinawa (Japan), Taiwan, and Thailand. During test observations conducted in Okinawa since 2021, no signal has been received that was clearly caused by anomalous propagation due to EPBs. This is simply because EPBs have not developed to high latitudes during the observation period due to the low solar activity. In March 2023, however, possible indications of EPB-related scattering were detected in Okinawa which implies the feasibility of observing EPBs with the current observation system. We plan to conduct pilot observations in Taiwan and Thailand in future to further evaluate the feasibility of this monitoring technique. Graphical Abstract: [Figure not available: see fulltext.]
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Identifying Geomagnetic Storms with Ionospheric Storm Scale for GNSS and Disaster Prevention
(2020-03-01)
Jamjareegulgarn, Punyawi
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Duangsuwan, Sarun
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Supnithi, Pornchai
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Budtho, Jirapoom
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Tangtrakunphaisan, Udomsit
This paper proposes an ionospheric storm scale (I-scale) for identifying the impact of geomagnetic or ionospheric storms in the Ionosphere for GNSS (global navigation satellite system) service and disaster prevention. The I-scale in this work is computed based on the observed foF2 at Chumphon station (10.72°N, 99.37°E) over equatorial latitude from January 2004 to July 2018. The results report that the severe geomagnetic storms, i.e., IP3 and IN3, seldom occur at Chumphon with the probabilities of 0.02% and 0.07%, respectively. The probability of quiet ionospheric condition is the maximum value of 70.73%. Meanwhile, the other I-scales sometimes occur and range from 0.60% to 13.97%. The benefits of the foF2-based I-scale are to indicate the violence level of geomagnetic storms and to announce the ionospheric irregularities in practice.
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The comparison of Klobuchar model with GPS TEC model at the low geomagnetic latitude station, Thailand
(2019-06-01)
Tongkasem, Napat
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Supnithi, Pornchai
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Phakphisut, Watid
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Hozumi, Kornyanat
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Tsugawa, Takuya
In the Global Positioning System (GPS), ionospheric delay time is a main cause of the positioning system errors. We can typically calculate the ionospheric delay using the dual-frequency receivers (L1: 1,575.42 MHz, L2: 1227.60 MHz). The Klobuchar model is a well-known model developed to estimate the ionospheric delay and currently used for single-frequency users. The coefficients of the model are daily broadcast in the GPS satellite navigation message for worldwide users. In this work, we compare the actual ionospheric delays with the Klobuchar model to observe the differences at 4 stations in Thailand: CMU (Chiang Mai), KMIT (Bangkok), CPN (Chumpon) and NNKI (Nongkai) on 10 February 2018 (no disturbance). Then, we compute the new Klobuchar coefficients from the comparisons. The proposed Klobuchar coefficients can correct the RMSE of the original model by 32.4, 36.5, 28.5 and 37.1 at KMIT, CPN, NNKI and CMU station, respectively. The RMSE of the new Klobuchar and observed TEC comparison are 24.0718, 28.5849, 21.6086 and 27.7273, respectively.
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Assessment of GPS-TEC with the IRI-2016 model, the IRI-Plas model and GIM-TEC during low solar activity at KMITL, Thailand
(2019-06-01)
Udomchaibanjerd, Jumpon
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Supnithi, Pornchai
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Phakphisut, Watid
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Hozumi, Kornyanat
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Tsugawa, Takuya
We have assessed the ionospheric total electron content (TEC) variations which derived from dual frequency GPS receivers (GPS-TEC) at the KMITL, Thailand, called KMIT station. Then, we study TEC variations during the quiet geomagnetic condition in the low solar cycle, 2008 which is the lowest solar activity of the 24<sup>th</sup> solar cycle. The GPS-TEC is compared with the TEC prediction by the IRI-Plas model, the IRI-2016 model and the Global Ionospheric Maps (GIMs) by the International GNSS Service (IGS). The International Reference Ionosphere (IRI-2016), International Reference Ionosphere extend plasmasphere (IRI-Plas) and Global Ionosphere Maps (GIM-TEC) are model predicted total electron content (TEC). Also, the IRI-Plas has the plasmasphere extension up to 20,000 km, closed to observation TEC from the global positioning system. The GPS-TEC underestimates the IRI-Plas and GIM-TEC in all seasons whereas the IRI-2016 overestimates the GPS-TEC except the IRI-2016 is comparable to the GPS-TEC between 20.00-24.00 UT.
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Total electron content observations by dense regional and worldwide international networks of GNSS
(2018-06-01)
Tsugawa, Takuya
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Nishioka, Michi
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Ishii, Mamoru
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Hozumi, Kornyanat
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Saito, Susumu
Two-dimensional ionospheric total electron content (TEC) maps have been derived from ground-based Global Navigation Satellite System (GNSS) receiver networks and applied to studies of various ionospheric disturbances since the mid-1990s. For the purpose of monitoring and researching ionospheric conditions and ionospheric space weather phenomena, we have developed TEC maps of areas over Japan using the dense GNSS network, GNSS Earth Observation NETwork (GEONET), which consists of about 1300 stations and is operated by the Geospatial Information Authority of Japan (GSI). Currently, we are providing high-resolution, two-dimensional maps of absolute TEC, detrended TEC, rate of TEC change index (ROTI), and loss-of-lock on GPS signal over Japan on a real-time basis. Such high-resolution TEC maps using dense GNSS receiver networks are one of the most effective ways to observe, on a scale of several 100 km to 1000 km, ionospheric variations caused by traveling ionospheric disturbances and/or equatorial plasma bubbles, which can degrade single-frequency and differential GNSS positioning/navigation. We have collected all the available GNSS receiver data in the world to expand the TEC observation area. Currently, however, dense GNSS receiver networks are available in only limited areas, such as Japan, North America, and Europe. To expand the two-dimensional TEC observation with high resolution, we have conducted the Dense Regional and Worldwide International GNSS TEC observation (DRAWING-TEC) project, which is engaged in three activities: (1) standardizing GNSS-TEC data, (2) developing a new high-resolution TEC mapping technique, and (3) sharing the standardized TEC data or the information of GNSS receiver network. We have developed a new standardized TEC format, GNSS-TEC EXchange (GTEX), which is included in the Formatted Tables of ITU-R SG 3 Data-banks related to Recommendation ITU-R P.311. Sharing the GTEX TEC data would be easier than sharing the GPS/GNSS data among those in the international ionospheric researcher community. The DRAWING-TEC project would promote studies of medium-scale ionospheric variations and their effect on GNSS.
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A new expression for computing topside scale height for satellite-based communications
(2017-10-19)
Jamjareegulgarn, Punyawi
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Supnithi, Pornchai
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Hozumi, Kornyanat
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Tsugawa, Takuya
It is well-known that the NeQuick 2 model provides analytical expressions showing a relationship between topside and bottomside ionospheres. Its bottomside thickness parameter (B2bot) is a key parameter for studying topside electron density profile (EDP) and topside parameters, and its topside scale height (Hsc) is also used to identify the topside electron density profile. The B2bot computed using ionogram-derived ionospheric parameters can be used to calculate the Hsc. Unfortunately, the Hsc computed by the original B2bot expression (Hsc old) are significantly higher than the scale heights obtained from digisondes (Hm) and the diurnal variations of the Hsc old are quite different from those of the Hm. Hence, a new expression of B2bot for computing the Hsc is suggested in this work relying on the available expressions of the NeQuick 2 model. Our results show that (1) the Hsc computed by the new expression of B2bot (Hsc new) are comparable to the Hm and the diurnal variations in Hsc new are the same trends as those in Hm; (2) all of the scale heights show diurnal variations with higher values during daytime than during nighttime and the secondary peaks can be found different local times relying on the locations; and (3) the peaks of scale height cause higher absolute differences between Hsc new and Hm (D SH).
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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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Statistical analysis of high frequency radio parameters on St. Patrick's day in Thailand
(2017-10-19)
Thammavongsy, Phimmasone
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Supnithi, Pornchai
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Klinngam, Somjai
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Phakphisut, Watid
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Hozumi, Kornyanat
The ionospheric irregularities on St. Patrick's day (17 March 2015) at Chiang Mai and Chumphon stations are affected by the strongest of the 24th solar storm cycle. The ionogram data in this research is obtained from the frequency modulated/carrier waves (FM/CW) ionosonde at Chiang Mai station and near the magnetic equator, namely, Chumphon station. The parameters in this research include the critical frequency of F2 layer, the virtual height of F layer, and the maximum height of F2 layer. Overall, we found that the ionosphere layer at Chiang Mai and Chumphon stations are disturbed by the geomagnetic storm. The result indicate that the radio frequency transmission is affected by geomagnetic storm at both stations and the observation differ from the median value is specified in part of the percentage of coefficient deviation.
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Ionospheric peak height at the magnetic equator: Comparison between ionosonde measurements and IRI
(2017-07-15)
Maruyama, Takashi
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Ma, Guanyi
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Tsugawa, Takuya
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Supnithi, Pornchai
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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.
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Study of ionospheric topside variations based on NeQuick topside formulation and comparisons with the IRI-2012 model at equatorial latitude station, Chumphon, Thailand
(2017-07-15)
Jamjareegulgarn, Punyawi
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Supnithi, Pornchai
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Hozumi, Kornyanat
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Tsugawa, Takuya
It is well-known that the equatorial anomaly at equatorial and low latitudes is caused by the fountain effect, therefore, the modeling of topside electron density profiles (EDPs) and the knowledge of electron density distribution in the region are particular challenging. Chumphon station, Thailand, is located within this region. However, at this station, since only an FMCW ionosonde system is installed, the topside EDP cannot be automatically obtained. Therefore, in this work, the topside EDPs are derived using the NeQuick topside formulation of the NeQuick 2 model (namely, NeQuick-derived topside EDPs) and then compared with those of three options of the IRI-2012 model including NeQuick, IRI01-corr, and IRI2001 options. The results show that, at Chumphon station, the NeQuick-derived topside EDPs are generally closer to the topside EDPs of IRI01-corr option in winter season and the topside EDPs of NeQuick option in equinox and summer seasons. When analyzing the topside TEC values obtained from each profile and the IGS TEC, it is found that the topside TEC values integrated from NeQuick-derived topside EDPs and predicted by both IRI01-corr and IRI-2001 options of the IRI-2012 model are sometimes higher than the IGS TEC values observed at Chumphon. In addition, we study the diurnal variations of the scale height computed from NeQuick topside formulation (H <inf>sc</inf> ), hmF2 and foF2 parameters. The correlation of H <inf>sc</inf> with the parameters hmF2 and the bottomside thickness parameter of NeQuick model (B2 <inf>bot</inf> ). The computed H <inf>sc</inf> values during daytime are lower than those during nighttime and they show non-linear correlations with hmF2 and B2 <inf>bot</inf> . The main cause of these discrepancies are possibly due to the B2 <inf>bot</inf> expressions used to compute the H <inf>sc</inf> .

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