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Global landscape of space weather observations, research and operations
(2025-01-01)
Ishii, Mamoru
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Costa, Joaquim E.R.
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Kuznetsova, Maria
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Bisi, Mario M.
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Meza, Amalia
The recognition of space weather hazards is increasingly growing, highlighting the importance of monitoring and forecasting it. High precision satellite positioning techniques have become essential in various areas of social and economic infrastructure. However, it is well-known that Global Navigation Satellite Systems (GNSS) can be affected by space weather-induced ionospheric variations. This poses a challenge as it can impact the reliability and accuracy of GNSS-based systems. Space weather phenomena can also have significant effects on aviation systems and electric power grids. Given that many of these phenomena occur on a global scale, it is crucial to have a comprehensive monitoring and observation network. Currently, numerous ground-based observations are managed by local government or academic bodies. In contrast, space-based observations are typically operated by space agencies, often necessitating international coordinated collaboration to undertake significant projects in this field. The paper puts a strong emphasis on the need for collaboration between various entities in each nation and between national programmes. In this paper, the authors provide an overview of the international landscape for space weather research and operations at the nation-state level. They also highlight the activities of various national and regional space agencies involved in space weather research and monitoring for enhancing our capabilities in monitoring, forecasting, and mitigating the impacts of space weather phenomena on critical infrastructure and systems.
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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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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 the bottomside thickness parameter and comparisons with the NeQuick and IRI-2012 models during declining phase of solar cycle 23 at equatorial latitude station, Chumphon, Thailand
(2017-07-15)
Jamjareegulgarn, Punyawi
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Supnithi, Pornchai
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Watthanasangmechai, Kornyanat
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Yokoyama, Tatsuhiro
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Tsugawa, Takuya
This paper proposes a new expression for computing the bottomside thickness parameter at equatorial latitude station, Chumphon (10.72°N, 99.37°E), Thailand. Its diurnal variations from 2004 to 2006 at this location are then studied. The proposed expression is derived based on two experimental data sources: FMCW ionosonde and dual-frequency GPS system, and some expressions of the NeQuick 2 model. Hence, after both the bottomside thickness parameter computed by the proposed equation, B2bot_Pro, and the bottomside shape parameter (namely, B1_Pro in this work) are computed, the bottomside electron density and the height where the bottomside electron density drops down to be 24% of the NmF2 (namely, h0.24) can be computed and shown in this work using the analytical functions of the IRI model. Moreover, the diurnal variations of the B2bot_Pro are compared with those computed from the NeQuick model, B2bot_NeQ, and the predicted B0 of the IRI-2012 model with ABT-2009 and Bil-2000 options (namely, “B0_ABT” and “B0_Bil”, respectively). The averaged, minimum, and maximum values of percentage deviations among these bottomside thickness parameters are also computed and shown in this work. Our results show that the diurnal variations of B2bot_Pro at Chumphon station have the following patterns: they start to increase during nighttime to the first peaks during pre-sunrise hours, and then decrease abruptly to their minimum values during sunrise hours. Afterward, they increase again to reach the second peaks around local noontime and fall gradually to their starting times during 20–04 LT. The diurnal variations of B2bot_Pro follow generally the same trends as those of the B2bot_NeQ and the B0_ABT, except pre-sunrise hours. The pre-sunrise peaks and sunrise collapses in both the B2bot_NeQ and the B0_ABT can be found occasionally. On the other hand, the diurnal variations in B2bot_Pro differ from those in B0_Bil due to the flattened variation in B0_Bil and the pre-sunrise peaks as well as sunrise collapses in B0_Bil disappear. The pre-sunrise peaks of the B2bot_Pro at the Chumphon station are higher than those of the B2bot_NeQ, the B0_ABT, and the observed B0 at other regions. Furthermore, the percentage deviations between the B2bot_Pro and the B0_ABT (PD_B2B0ABT) are mostly lower than 30% for all seasons of the studied years, opposite to the other percentage deviations studied in this work. The proposed B2bot_Pro parameters in this work follow a similar trend to the B2bot_NeQ and the B0_ABT, but it is not conclusive that the proposed values are equivalent to them.
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Estimation of the single GPS-receiver bias using the gradient descent algorithm
(2016-09-06)
Chiablaem, Athiwat
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Supnithi, Pornchai
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Klinngam, Somjai
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Panachart, Chaiwat
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Saekow, Apithep
The ionospheric Total Electron Content (TEC) can be obtained from processing measurements of the dual-frequency Global Positioning System (GPS) receiver. The main sources of errors in the TEC calculation are satellite and receiver biases. In this paper, we apply the gradient descent algorithm on the receiver bias estimation. The TEC is derived from measurements at 12 dual-frequency GPS stations in Thailand. The criterion of receiver bias estimation is based on the minimum sum of the vertical TEC (VTEC) standard deviation method. The results show that the maximum receiver bias value is approximately 3.69 ns at UDON station, while the minimum value is -5.91 ns at SRTN station. The accuracy of the receiver biases from this algorithm is compared with the reference method. The maximum percentage deviation is about 7.5% at SRTN station. The percentage deviation of the minimum sum of the VTEC between the reference method and the proposed method from all stations are less than 0.05%. Thus, the proposed algorithm is a viable option to estimate the receiver bias.
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Predawn plasma bubble cluster observed in Southeast Asia
(2016-06-01)
Watthanasangmechai, Kornyanat
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Yamamoto, Mamoru
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Saito, Akinori
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Tsunoda, Roland
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Yokoyama, Tatsuhiro
Predawn plasma bubble was detected as deep plasma depletion by GNU Radio Beacon Receiver (GRBR) network and in situ measurement onboard Defense Meteorological Satellite Program F15 (DMSPF15) satellite and was confirmed by sparse GPS network in Southeast Asia. In addition to the deep depletion, the GPS network revealed the coexisting submesoscale irregularities. A deep depletion is regarded as a primary bubble. Submesoscale irregularities are regarded as secondary bubbles. Primary bubble and secondary bubbles appeared together as a cluster with zonal wavelength of 50 km. An altitude of secondary bubbles happened to be lower than that of the primary bubble in the same cluster. The observed pattern of plasma bubble cluster is consistent with the simulation result of the recent high-resolution bubble (HIRB) model. This event is only a single event out of 76 satellite passes at nighttime during 3–25 March 2012 that significantly shows plasma depletion at plasma bubble wall. The inside structure of the primary bubble was clearly revealed from the in situ density data of DMSPF15 satellite and the ground-based GRBR total electron content.
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A comparative study of ionospheric profile parameters B0 and B1 over Chumphon with IRI-2012
(2015-08-17)
Jamjareegulgarn, Punyawi
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Supnithi, Pornchai
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Wichaipanich, Noraset
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Ishii, Mamoru
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Maruyama, Takashi
Average diurnal variations of ionospheric profile parameters B0 and B1 in 2009 are studied over Chumphon province, Thailand, and compared those variations with IRI-2012 model. The thickness parameter (B0) and the shape parameter (B1) are two main parameters to compute and depict the F2-layer electron density profile. IRI-2012, the latest version of IRI model, offers three options to provide B0 and B1, i.e., Bil-2000, Gul-1987, ABT-2009. Those options have never been taken for studying and comparing with the ionospheric observation data from a FM/CW ionosonde, Chumphon. Moreover, the observed B0 and B1 from Thailand have never been analyzed nor used while establishing the new table of (B0, B1) values of the IRI model. Hence, B0 and B1 observation is necessary as a part of the global validation study of the IRI-2012 model. Our studies show that: (1) In general, the average diurnal variations of B0 for the observation and the IRI-2012 model show the same trends, except B0 of Gul-1987 during 20:00 - 02:00 LT. The observed B0 averages are equal to 166.13 km and 99.18 km in the daytime and nighttime, respectively. (2) The average diurnal variations of B1 for the observation and the IRI-2012 model show the same trends, except B1 of ABT-2009. Average diurnal variations of the observed B1 look like a sine wave where the peak and lowest values can be found around the midnight and the noontime, respectively. For the IRI-2012 model, B1 of Gul-1987 is the same value as B1 of Bil-2000. The observed B1 averages are equal to 1.98 and 2.51 in the daytime and nighttime, respectively. Our observed B0 and B1 results are similar to other studies in equatorial latitude and low latitude stations. Our comparative studies provide some details for improving B0 and B1 parameters of CCIR-based IRI model in the equatorial latitude region.
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The occurrence of equatorial spread-F at conjugate stations in Southeast Asia
(2015-04-15)
Klinngam, Somjai
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Supnithi, Pornchai
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Rungraengwajiake, Sarawoot
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Tsugawa, Takuya
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Ishii, Mamoru
In this study, the probability of equatorial spread-F (ESF) occurrence at the conjugate stations in Southeast Asia: Chiangmai station (CMU), Thailand, and Kototabang station (KTB), Indonesia, and near the magnetic equator, Chumphon station (CPN), Thailand, is presented. We analyze the ionogram data recorded by the Frequency Modulated Continuous Wave (FM/CW) ionosondes for the periods of minimum solar activity from September 2008 to April 2009 and in the equinoctial months (March and April) from 2006 to 2013. The spread-F signatures are manually categorized into three types: the frequency spread-F (FSF), the range spread-F (RSF) and the mixed spread-F (MSF) and the monthly average percentage of the occurrence of each ESF type is presented. The results show that the percentage of RSF occurrence at CPN, which is located around the magnetic equator, is higher than at other stations and the RSF mostly occurs during the equinoctial months. On the other hand, the FSF occurrence at CMU and KTB, that are located in the northern and southern hemispheres, respectively, are higher than at CPN. The RSF occurrence typically has the peaks before midnight, while the maximum occurrence rate of FSF is after midnight. Furthermore, the RSF onsets normally precede the FSF onsets by about 1-2 h. As the solar activity levels go up, the percentages of RSF occurrence increase, but the percentages of FSF tends to decrease. In addition, we compare the statistics of observed RSF occurrence with the prediction of the IRI-2012 model. The results show that the IRI model overestimates the observed RSF occurrence at all stations during most of the solar activity levels and seasons, except in June 2008 (21:00-03:00 LT), March 2011 (23:30-01:00 LT) and March 2013 (01:00-02:30 LT) when the IRI model underestimates our observations. However, the IRI model gives closer probability of RSF occurrence to our observed values at CPN, especially in equinoctial months and during the periods of medium solar activity. This work is important for an improvement of the IRI model in the prediction of the spread F occurrence probability in the low-latitude region.
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Low-latitude ionospheric height variation as observed by meridional ionosonde chain: Formation of ionospheric ceiling over the magnetic equator
(2014-01-01)
Maruyama, Takashi
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Uemoto, Jyunpei
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Ishii, Mamoru
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Tsugawa, Takuya
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Supnithi, Pornchai
A multipoint ionosonde observation campaign was conducted along the magnetic meridional plane in Southeast Asia to study ionosphere-thermosphere coupling. One station was near the magnetic equator and two of the other stations were at off-equatorial latitudes (∼10° magnetic latitude). The daytime ionospheric peak height (h<inf>m</inf>F<inf>2</inf>) was analyzed for each season during the solar minimum years, 2006-2007 and 2009. The peak height increased for ∼3 h after sunrise at the magnetic equator and off-equatorial latitudes, as expected from the daytime upward E × B drift. The apparent upward drift at the magnetic equator ceased before noon, while the drift at the off-equatorial latitudes continued upward and the layer height exceeded the equatorial height around noon. The noontime limited layer peak height at the magnetic equator, which was termed the ionospheric ceiling, did not depend on the season, while the maximum peak height at the off-equatorial latitudes largely varied with each season. Numerical modeling using the SAMI2 code was conducted and the features of the ionospheric ceiling were reproduced quite well. The dynamical parameters provided by the SAMI2 modeling runs showed that the ionospheric ceiling is formed by the field-aligned plasma diffusion, which is a part of the fountain effect. Key Points Multipoint ionosonde observation along the magnetic meridian in Southeast Asia Noontime restricted F layer peak height at the magnetic equator Revisiting the equatorial anomaly from the viewpoint of height variations
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Ionospheric variation at Thailand equatorial latitude station: Comparison between observations and IRI-2001 model predictions
(2010-01-15)
Wichaipanich, Noraset
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Supnithi, Pornchai
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Ishii, Mamoru
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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.

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