Faculty Profiles - SHINBORI Atsuki

Papers - SHINBORI Atsuki

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Regional Ionospheric Super Bubble Induced by Significant Upward Plasma Drift During the 1 December 2023 Geomagnetic Storm Reviewed International coauthorship Open Access

Wenjie Sun, Guozhu Li, Shun Rong Zhang, Lianhuan Hu, Guofeng Dai, Biqiang Zhao, Yuichi Otsuka, Xiukuan Zhao, Haiyong Xie, Yi Li, Baiqi Ning, Libo Liu, Atsuki Shinbori, Michi Nishioka, Septi Perwitasari

Journal of Geophysical Research: Space Physics Vol. 129 ( 6 ) 2024.6

Language：English Publishing type：Research paper (scientific journal)

An unseasonal equatorial plasma bubble (EPB) event occurred in the East/Southeast Asian sector during the geomagnetic storm on 1 December 2023, causing strong amplitude scintillations from equatorial to middle latitudes. Based on the observations from multiple instruments over a large latitudinal and longitudinal region, the spatial features of the super EPB were investigated. The EPB developed vertically at a fast rising speed ∼470 m/s over the magnetic equator and extended to a very high middle latitude more than 40°N, despite that the storm intensity was not very strong with the minimum SYM-H index −132 nT. In the zonal direction, the super EPB covered over a specific region ∼95–140°E, where the local sunset roughly coincided with southward turning of interplanetary magnetic field (IMF) Bz component. Before the onset of the super EPB, significant upward plasma drift up to ∼110 m/s was observed over the magnetic equator, which could amplify the growth rate of Rayleigh-Taylor instability and lead to the generation of the super EPB. The significant drift was likely caused by eastward penetration electric field (PEF) due to sharp southward turning of IMF Bz. The local time of storm onset and duration of IMF Bz southward turning during the storm main phase may partly determine the onset region and zonal coverage of the EPB.

DOI： 10.1029/2024JA032430

Thermospheric Wind Response to March 2023 Storm: Largest Wind Ever Observed With a Fabry-Perot Interferometer in Tromsø, Norway Since 2009 Reviewed International coauthorship

Oyama, S; Vanhamäki, H; Cai, L; Shinbori, A; Hosokawa, K; Sakanoi, T; Shiokawa, K; Aikio, A; Virtanen, II; Ogawa, Y; Miyoshi, Y; Kurita, S; Nishitani, N

SPACE WEATHER-THE INTERNATIONAL JOURNAL OF RESEARCH AND APPLICATIONS Vol. 22 ( 3 ) 2024.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Space Weather

Solar cycles 24–25 were quiet until a geomagnetic storm with a Sym-H index of −170 nT occurred in late March 2023. On March 23–24, a Fabry-Perot interferometer (FPI; 630 nm) in Tromsø, Norway, recorded the highest thermospheric wind speed of over 500 m/s since 2009. Comparisons with magnetometer readings in Scandinavia showed that a large amount of electromagnetic energy was transferred to the ionosphere-thermosphere system. Total electron content maps suggested an enlarged auroral oval and revealed that the FPI observed winds near the polar cap instead of inside the oval for a long period during the storm main phase. The FPI wind had a strong equatorward component during the storm, likely because of the powerful anti-sunward ionospheric plasma flow in the polar cap. The positive Y-component of the IMF for 6 days before the storm caused a successive westward component of the FPI-measured wind during the storm main phase. On March 24, the first day of the storm recovery phase, thermospheric wind disturbed and the ionospheric density decreased significantly at high latitudes. This density depression lasted for several days, and a large amount of electromagnetic energy during the storm modified the thermospheric dynamics and ionospheric plasma density.

DOI： 10.1029/2023SW003728

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Performance of the double-thin-shell approach for studying nighttime medium-scale traveling ionospheric disturbances using two dense GNSS observation networks in Japan Reviewed

Fu, WZ; Otsuka, Y; Shinbori, A; Nishioka, M; Perwitasari, S

EARTH PLANETS AND SPACE Vol. 76 ( 1 ) 2024.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Earth, Planets and Space

Electrodynamic coupling between the ionospheric E and F regions is widely recognized as the underlying mechanism for generating medium-scale traveling ionospheric disturbances (MSTIDs) during nighttime at midlatitudes. Recently, the double-thin-shell approach has proven to be a useful tool for studying the E–F coupling. By using total electron content (TEC) measurements, this approach enables the simultaneous reconstruction of electron density perturbations in both the E and F regions with broad and continuous coverage. However, the current reconstruction performance is limited when using only GPS-TEC measurements from GEONET, a dense network of ground-based Global Navigation Satellite System (GNSS) receivers over Japan. The expansion of available data sources and the integration of multi-GNSS observation data are considered important to enhance the double-thin-shell model. Fortunately, SoftBank Corp., a Japanese telecommunications provider, has recently developed a dense independent GNSS observation network to improve positioning services. In this paper, we analyze the potential of the improved double-thin-shell approach and emphasize the importance of incorporating multi-GNSS observation data from both GEONET and SoftBank networks. The solvability analysis, simulation, and observation results collectively indicate a substantial improvement in the spatiotemporal resolution. Specifically, the longitudinal and latitudinal resolution is improved from 0.15° to 0.1° in the E region, and from 0.5° to 0.3° in the F region. The temporal resolution is also improved from 2 to 1 min. In addition, significant improvements have been achieved in the reconstruction performance, particularly for the E region under complex background conditions. Based on these assessments, we conclude that the incorporation of GEONET and SoftBank GNSS observation data holds significant potential for improving the double-thin-shell model and advancing our understanding of MSTIDs. Graphical abstract: [Figure not available: see fulltext.]

DOI： 10.1186/s40623-023-01956-8

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Statistical Analysis of Global and Regional Ionospheric Total Electron Content (TEC) Using Extreme Value Distributions Reviewed International coauthorship

Emmela, S; Ratnam, DV; Otsuka, Y; Shinbori, A; Sori, T; Nishioka, M; Perwitasari, S

IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING Vol. 62 page： 1 - 8 2024

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Geoscience and Remote Sensing

Satellite-based radio communication and navigation systems rely mostly on transionospheric propagation of radio signals concerning changes by total electron content (TEC). Therefore, it is necessary to understand the changing behavior of structural variations of ionospheric TEC for high-frequency applications besides mitigating the risks associated with the space weather impacts for navigation and aviation applications. The reference thresholds identified for moderate and severe levels of threshold activity for TEC by the International Civil Aviation Organization (ICAO) are 125 and 175 TECU, respectively. In view of this, statistical analysis of long-term ground-based global navigation satellite system (GNSS) TEC data of 25 years (1997-2021) using extreme value theory (EVT) is performed for both magnetically quiet and disturbed day conditions for four different regions - India (5-45°N), Japan low (20-30°N), Japan mid-latitudes (30-50°N), and global regions to identify the extreme ionospheric TEC events that take place once in 11, 22, 44, 66, 88, and 110 years with 95% confidence intervals. In the present work, both generalized extreme value (GEV) using annual maxima and generalized Pareto distribution (GPD) using peak-over-threshold (PoT) analysis are performed. A likelihood test and PoT constraint in addition to adjustment of shape parameter illustrate that GPD works better than GEV to identify return periods of extreme events. The recommended TEC moderate and severe thresholds for India, Japan low, Japan mid-latitude, and global regions are 121, 101, 90, and 139 TECU and 131, 135, 98, and 157 TECU, respectively. The analysis would be helpful in developing risk assessment and mitigation strategies for critical (GNSS) space weather systems.

DOI： 10.1109/TGRS.2023.3338513

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A Survey on Databases of Specialized Fields and Research Data in Nagoya University Reviewed

NAOE Chizuko, NOSÉ Masahito, SHINBORI Atsuki, MIYOSHI Yoshizumi, HORI Tomoaki, HASHIBA Junko, OHIRA Tsukasa, GAKIYA Rui, OKAMOTO Maiko, SAGARA Takeshi

The Journal of Information Science and Technology Association Vol. 74 ( Special_Issue ) page： 2024-002 - 2024-002 2024

Multi-Instrument Observations of the Evolution of Polar Cap Patches Associated With Flow Shears and Particle Precipitation Reviewed International coauthorship

Zhang, D; Zhang, QH; Oksavik, K; Xing, ZY; Lyons, LR; Yang, HG; Li, GJ; Hosokawa, K; Shinbori, A; Ma, YZ; Wang, Y; Wang, XY

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 128 ( 12 ) 2023.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

Simultaneous observations from Defense Meteorological Satellite Program, Swarm, Resolute Bay all-sky imagers, GPS Total Electron Content and Super Dual Auroral Radar Network, are used to investigate the evolution and key characteristics of the Tongue of Ionization (TOI) being restructured into a polar cap patch. Six satellites crossed the TOI of patch as it moved from the dayside to the nightside. It was initially hot, then a mix of both cold and hot, and finally it became a cold patch. This suggests that cold patch is not only a result of solar extreme ultraviolet radiation, but may also develop when a hot patch cools down. Soft-electron precipitation and flow shears both contribute to the TOI restructuring and the appearance of polar cap patch. The plasma density of patch at ∼500 km was at least 4 times higher than at ∼800 km. The plasma density enhancement gradually decreased as the patch evolved due to decreased production and transport of cold nightside low-density plasma. Moreover, the duskward motion of the patch was influenced by changes in the ionospheric convection pattern.

DOI： 10.1029/2023JA032176

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New aspects of the upper atmospheric disturbances caused by the explosive eruption of the 2022 Hunga Tonga–Hunga Ha’apai volcano Invited Reviewed

A. Shinbori, Y. Otsuka, T. Sori, M. Nishioka, S. Perwitasari, T. T. Tsuda, N. Nishitani, A. Kumamoto, F. Tsuchiya, S. Matsuda, Y. Kasahara, A. Matsuoka, S. Nakamura, Y. Miyoshi, I. Shinohara

Earth Planets Space Vol. 75 ( 1 ) page： 175 2023.11

Spatio-Temporal Characteristics of IPDP-Type EMIC Waves on April 19, 2017: Implications for Loss of Relativistic Electrons in the Outer Belt Reviewed International coauthorship Open Access

Asuka Hirai, Fuminori Tsuchiya, Takahiro Obara, Yuto Katoh, Yoshizumi Miyoshi, Kazuo Shiokawa, Yasumasa Kasaba, Hiroaki Misawa, Chae Woo Jun, Satoshi Kurita, Martin G. Connors, Aaron T. Hendry, Atsuki Shinbori, Yuichi Otsuka, Takuya Tsugawa, Michi Nishioka, Septi Perwitasari, Jerry W. Manweiler

Journal of Geophysical Research: Space Physics Vol. 128 ( 8 ) 2023.8

Language：English Publishing type：Research paper (scientific journal)

To understand the mechanism of the increased frequency of intervals of pulsations of diminishing periods (IPDPs), we analyzed IPDP-type electromagnetic ion cyclotron (EMIC) waves that occurred on 19 April 2017, using ground and satellite observations. Observations by low-altitude satellites and ground-based magnetometers indicate that the increased IPDP frequency is caused by an inward (i.e., Earthward) shift of the EMIC wave source region. The EMIC wave source region moves inward along the mid-latitude trough, which we used as a proxy for the plasmapause location. A statistical analysis shows that increases in the IPDP frequency showed a positive correlation with polar cap potentials. These results suggest an enhanced convection electric field causes an inward shift of the source region. The inward shift of the source region allows EMIC waves to scatter relativistic electrons over a wide range of radial distances during the IPDP event. This mechanism suggests that IPDP-type EMIC waves are more likely to scatter relativistic electrons than other EMIC waves. We also show that the decreased phase-space density of relativistic electrons in the outer radiation belt is consistent with the extent of the source region and the resonant energy of EMIC waves, implying a possible contribution of EMIC waves to outer radiation belt loss during the main phase of geomagnetic storms.

DOI： 10.1029/2023JA031479

IMF Dependence of Midnight Bifurcation in the Thermospheric Wind at an Auroral Latitude Based on Nine Winter Measurements in Tromsø, Norway Reviewed International coauthorship

S. Oyama, K. Hosokawa, H. Vanhamäki, A. Aikio, T. Sakanoi, L. Cai, I. I. Virtanen, K. Shiokawa, N. Nishitani, A. Shinbori, Y. Ogawa

Geophysical Research Letters Vol. 50 ( 14 ) 2023.7

磁気圏－電離圏結合過程の基本原理とその未解明問題 Reviewed

新堀淳樹

page： 1 - 24 2023.6

Generation of equatorial plasma bubble after the 2022 Tonga volcanic eruption Reviewed

Shinbori Atsuki, Sori Takuya, Otsuka Yuichi, Nishioka Michi, Perwitasari Septi, Tsuda Takuo, Kumamoto Atsushi, Tsuchiya Fuminori, Matsuda Shoya, Kasahara Yoshiya, Matsuoka Ayako, Nakamura Satoko, Miyoshi Yoshizumi, Shinohara Iku

Scientific Reports Vol. 13 2023.5

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal)

Equatorial plasma bubbles are a phenomenon of plasma density depletion with small-scale density irregularities, normally observed in the equatorial ionosphere. This phenomenon, which impacts satellite-based communications, was observed in the Asia-Pacific region after the largest-on-record January 15, 2022 eruption of the Tonga volcano. We used satellite and ground-based ionospheric observations to demonstrate that an air pressure wave triggered by the Tonga volcanic eruption could cause the emergence of an equatorial plasma bubble. The most prominent observation result shows a sudden increase of electron density and height of the ionosphere several ten minutes to hours before the initial arrival of the air pressure wave in the lower atmosphere. The propagation speed of ionospheric electron density variations was ~ 480–540 m/s, whose speed was higher than that of a Lamb wave (~315 m/s) in the troposphere. The electron density variations started larger in the Northern Hemisphere than in the Southern Hemisphere. The fast response of the ionosphere could be caused by an instantaneous transmission of the electric field to the magnetic conjugate ionosphere along the magnetic field lines. After the ionospheric perturbations, electron density depletion appeared in the equatorial and low-latitude ionosphere and extended at least up to ±25° in geomagnetic latitude.

DOI： 10.1038/s41598-023-33603-3

CiNii Research

Geomagnetic activity dependence and dawn-dusk asymmetry of thermospheric winds from 9-year measurements with a Fabry–Perot interferometer in Tromsø, Norway Reviewed International coauthorship Open Access

Shin ichiro Oyama, Anita Aikio, Takeshi Sakanoi, Keisuke Hosokawa, Heikki Vanhamäki, Lei Cai, Ilkka Virtanen, Marcus Pedersen, Kazuo Shiokawa, Atsuki Shinbori, Nozomu Nishitani, Yasunobu Ogawa

Earth, Planets and Space Vol. 75 ( 1 ) 2023.5

Language：English Publishing type：Research paper (scientific journal)

Ion drag associated with the ionospheric plasma convection plays an important role in the high-latitude thermospheric dynamics, yet changes in the thermospheric wind with geomagnetic activity are not fully understood. We performed a statistical analysis of the thermospheric wind measurements with a Fabry–Perot interferometer (FPI; 630 nm wavelength) in Tromsø, Norway, in the winter months for 9 years. The measurements were sorted by a SuperMAG (SME) index, and a quiet-time wind pattern was defined as an hourly mean under SME ≤ 40 nT. The quiet-time wind pattern can be expected to be represented by a pressure gradient associated with the solar radiation and a geostrophic force balance. With an increase in the geomagnetic activity level, the thermospheric wind turned over from eastward to westward at dusk and increased the equatorward magnitude from midnight to dawn. Deviations from the quiet-time wind presented similar patterns in the direction with the ionospheric plasma convection but were larger in magnitude at dusk than at dawn. This is the first study to report a dawn-dusk asymmetry of the thermospheric wind acceleration feature and signatures of the eastward wind acceleration at dawn by ion drag. Graphical Abstract: [Figure not available: see fulltext.].

DOI： 10.1186/s40623-023-01829-0

First Detection of Midlatitude Plasma Bubble by SuperDARN During a Geomagnetic Storm on May 27 and 28, 2017 Reviewed

Sori, T; Shinbori, A; Otsuka, Y; Nishioka, M; Perwitasari, S; Nishitani, N

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 128 ( 4 ) 2023.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

We used the global navigation satellite system-total electron content (TEC) and Super Dual Auroral Radar Network (SuperDARN) radar to elucidate the characteristics of the plasma bubble extending to midlatitudes over North America during a geomagnetic storm on 27 and 28 May 2017. To identify plasma bubbles, we analyzed the rate of the TEC index (ROTI), which is a good indicator of the occurrence of plasma bubbles. The enhanced ROTI region expanded up to 50°N (geomagnetic latitude), and the upper limit of this region coincided with the equatorward wall of the midlatitude trough. Two-dimensional ROTI maps show that the enhanced midlatitude ROTI region moved westward at a bulk speed of approximately 310 m/s. The Fort Hays East SuperDARN radar also detected the radar echo, showing the existence of plasma density irregularities at ∼10-m scales within the midlatitude plasma bubble. The radar echo had a westward velocity of ∼300 m/s, which is almost consistent with the westward motion of the enhanced midlatitude ROTI region. We deduced that the westward propagation of the plasma bubble could be caused by a poleward sub-auroral polarization stream electric field. The observed radar echo overlapping with the enhanced ROTI region had a narrower spectral width (<50 m/s) than that of the auroral activity. This feature resembled that of the type 1 echo, although the Doppler velocity was smaller than the ion acoustic speed at the F-region height. This is the first case in which plasma density irregularities within plasma bubbles were captured by the SuperDARN radar.

DOI： 10.1029/2022JA031157

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Statistical analysis for EUV dynamic spectra and their impact on the ionosphere during solar flares Reviewed International journal

Shohei Nishimoto, Kyoko Watanabe, Hidekatsu Jin, Toshiki Kawai, Shinsuke Imada, Tomoko Kawate, Yuichi Otsuka, Atsuki Shinbori, Takuya Tsugawa, Michi Nishioka

Earth, Planets and Space Vol. 75 ( 1 ) 2023.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Springer Science and Business Media LLC

Abstract

The X-rays and extreme ultraviolet (EUV) emitted during solar flares can rapidly change the physical composition of Earth’s ionosphere, causing space weather phenomena. It is important to develop an accurate understanding of solar flare emission spectra to understand how it affects the ionosphere. We reproduced the entire solar flare emission spectrum using an empirical model and physics-based model, and input it into the Earth’s atmospheric model, GAIA to calculate the total electron content (TEC) enhancement due to solar flare emission. We compared the statistics of nine solar flare events and calculated the TEC enhancements with the corresponding observed data. The model used in this study was able to estimate the TEC enhancement due to solar flare emission with a correlation coefficient greater than 0.9. The results of this study indicate that the TEC enhancement due to solar flare emission is determined by soft X-ray and EUV emission with wavelengths shorter than 35 nm. The TEC enhancement is found to be largely due to the change in the soft X-ray emission and EUV line emissions with wavelengths, such as Fe XVII 10.08 nm, Fe XIX 10.85 nm and He II 30.38 nm.

Graphical Abstract

DOI： 10.1186/s40623-023-01788-6

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Other Link： https://link.springer.com/article/10.1186/s40623-023-01788-6/fulltext.html

Dependence of Ionospheric Responses on Solar Wind Dynamic Pressure During Geomagnetic Storms Using Global Long-Term GNSS-TEC Data Reviewed

Sori, T; Shinbori, A; Otsuka, Y; Nishioka, M; Perwitasari, S

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 128 ( 3 ) 2023.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

To elucidate the effect of solar wind dynamic pressure on the activities of ionospheric plasma irregularities in both high-latitude and equatorial regions, we analyzed the long-term global navigation satellite system (GNSS) total electron content (TEC) data from 2000 to 2018 and performed a superposed epoch analysis of the GNSS rate of the TEC index (ROTI), solar wind, interplanetary magnetic field (IMF), and geomagnetic index. We found that during the main phase of geomagnetic storms, the activities of ionospheric plasma irregularities were considerably enhanced in both high-latitude and equatorial regions under high-pressure conditions, and the equatorward edge of the auroral oval moved to lower latitudes. The poleward edge of the enhanced low-latitude ROTI region (occurrence region of the plasma bubbles) in the evening sector extended to higher latitudes under high-pressure conditions. During the recovery phase of geomagnetic storms, the plasma bubble occurrence in the dusk sector was suppressed under high-pressure conditions. Our results suggest that the high-latitude convection electric field and the penetration and disturbance dynamo electric fields at low latitudes become stronger during geomagnetic storms when the solar wind dynamic pressure is enhanced. This is because the conversion from solar wind energy to electromagnetic energy in the magnetosphere is enhanced by the formation of a high plasma pressure area in the high-latitude cusp and mantle region. Therefore, not only the southward IMF but also solar wind dynamic pressure are important factors for varying global ionospheric responses during geomagnetic storms.

DOI： 10.1029/2022JA030913

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Multi-Event Analysis of Magnetosphere-Ionosphere Coupling of Nighttime Medium-Scale Traveling Ionospheric Disturbances From the Ground and the Arase Satellite Reviewed International coauthorship Open Access

K. Kawai, K. Shiokawa, Y. Otsuka, S. Oyama, M. G. Connors, Y. Kasahara, Y. Kasaba, S. Nakamura, F. Tsuchiya, A. Kumamoto, A. Shinbori, A. Matsuoka, I. Shinohara, Y. Miyoshi

Journal of Geophysical Research: Space Physics Vol. 128 ( 2 ) 2023.2

Language：English Publishing type：Research paper (scientific journal)

Kawai et al. (2021) reported the first ground-satellite conjugate observation of nighttime medium-scale traveling ionospheric disturbances (MSTIDs), by analyzing measurements from an airglow imager at Gakona (geographic latitude: 62.39°N, geographic longitude: 214.78°E, magnetic latitude: 63.60°N) and the Arase satellite in the magnetosphere on 3 November 2018. The Arase satellite observed variations in both the polarization electric field and the electron density as the Arase footprint passed through the MSTID structures in the ionosphere. In this study, we investigated whether these electric field and density variations associated with MSTIDs at subauroral latitudes are always observed by Arase in the magnetosphere. We used three airglow imagers installed at Gakona, Athabasca (geographic latitude: 54.60°N, geographic longitude: 246.36°E, magnetic latitude: 61.10°N), and Kapuskasing (geographic latitude: 49.39°N, geographic longitude: 277.81°E, magnetic latitude: 58.70°N) and the Arase satellite. We found eight observations of MSTIDs conjugate with Arase. They indicate that electric field and density variations associated with MSTIDs are not always observed in the magnetosphere. These variations tend to be observed in the magnetosphere during geomagnetically quiet times and when the amplitude of the MSTID is large. We categorized the MSTIDs into those caused by plasma instabilities and gravity waves and found that the electric field and density variations can be observed in the magnetosphere for both types of MSTIDs.

DOI： 10.1029/2022JA030542

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Advanced tools for guiding data‐led research processes of Upper‐Atmospheric phenomena Reviewed

Yoshimasa Tanaka, Norio Umemura, Shuji Abe, Atsuki Shinbori, Satoru UeNo

Geoscience Data Journal Vol. 10 ( 1 ) page： 130 - 141 2023.1

An Extreme Value Analysis of Long-Term GNSS Ionospheric Total Electron Content Data Observed at Japan Grid Point Location (34.95° N and 134.05° E) Reviewed International coauthorship

Emmela, S; Ratnam, DV; Otsuka, Y; Shinbori, A; Sori, T; Nishioka, M; Perwitasari, S

IEEE GEOSCIENCE AND REMOTE SENSING LETTERS Vol. 20 2023

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Geoscience and Remote Sensing Letters

Space weather adversely affects satellite systems by obstructing the services of global positioning systems (GPSs), delaying the launch of space vehicles, and causing damage to basic infrastructures such as radio-communications and power distribution networks. The spatio-temporal variations of ionospheric total electron content (TEC) during geomagnetic storms can be well examined by extreme value analysis. Statistical assessment and analysis of extreme values are necessary for developing risk assessment and mitigation strategies to the affected communication systems. In this study, extreme TEC events are investigated using 25 years (1997-2021) of long-term Global Navigation Satellite System (GNSS) Earth Observation Network System (GEONET) TEC data over Japan grid point location at 34.95° N and 134.05° E, and global data. In this work, a generalized extreme value (GEV) distribution is applied to the annual maxima TEC to evaluate geomagnetic disturbances that could occur once in 44, 88, 132, and 176 years with a confidence interval of 95%. According to the reference thresholds indicated by International Civil Aviation Organization (ICAO) for safer aviation applications, the moderate and severe levels of threshold for TEC are identified as 125 and 175 TEC Units (TECU), respectively. The results illustrate that the estimated extreme TECs for one in 44, 88, 132, and 176 years are 119, 125, 128, 130 and 215, 220, 222, 225 TECU for grid point and global TEC data respectively. That is, a moderate threshold level of activity is likely to happen over considered grid point for a return period of beyond 88 years and severe threshold level of activity beyond 11 years for global TEC data.

DOI： 10.1109/LGRS.2023.3292593

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Oscillations of the Ionosphere Caused by the 2022 Tonga Volcanic Eruption Observed With SuperDARN Radars Reviewed

Zhang, JJ; Xu, JY; Wang, W; Wang, GJ; Ruohoniemi, JM; Shinbori, A; Nishitani, N; Wang, C; Deng, X; Lan, AL; Yan, JY

GEOPHYSICAL RESEARCH LETTERS Vol. 49 ( 20 ) 2022.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Geophysical Research Letters

On 15 January 2022, the submarine volcano on the southwest Pacific island of Tonga violently erupted. Thus far, the ionospheric oscillation features caused by the volcanic eruption have not been identified. Here, observations from the Super Dual Auroral Radar Network radars and digisondes were employed to analyze ionospheric oscillations in the Northern Hemisphere caused by the volcanic eruption in Tonga. Due to the magnetic field conjugate effect, the ionospheric oscillations were observed much earlier than the arrival of surface air pressure waves, and the maximum negative line-of-sight (LOS) velocity of the ionospheric oscillations exceeded 100 m/s in the F layer. After the surface air pressure waves arrived, the maximum LOS velocity in the E layer approached 150 m/s. A maximum upward displacement of 100 km was observed in the ionosphere. This work provides a new perspective for understanding the strong ionospheric oscillation caused by geological hazards observed on Earth.

DOI： 10.1029/2022GL100555

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Thermospheric wind response to a sudden ionospheric variation in the trough: Event at a pseudo breakup during geomagnetically quiet conditions Reviewed Open Access

S.-i. Oyama, H. Vanhamäki, L. Cai, A. Aikio, M. Rietveld, Y. Ogawa, T. Raita, M. Kellinsalmi, K. Kauristie, B. Kozelov, A. Shinbori, K. Shiokawa, T. T. Tsuda, T. Sakanoi

Earth Planets Space Vol. 74 ( 1 ) page： 154 2022.10

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

The thermospheric wind response to a sudden westward turning of the ion velocity at a high latitude was studied by analyzing data obtained with a Fabry-Perot interferometer (FPI; 630 nm), Dynasonde, and Swarm A & C satellites during a conjunction event. The event occurred during a geomagnetically quiet period (Kp= 0+) through the night, but some auroral activity occurred in the north. The collocated FPI and Dynasonde measured the thermospheric wind (U) and ionospheric plasma velocity (V), respectively, in the F region at the equatorward trough edge. A notable scientific message from this study is the possible role of thermospheric wind in the energy dissipation process at F-region altitude. The FPI thermospheric wind did not instantly follow a sudden V change due to thermospheric inertia in the F region. At a pseudo-breakup during the event, V suddenly changed direction from eastward to westward within 10 min. U was concurrently accelerated westward, but its development was more gradual than that of V, with U remaining eastward for a while after the pseudo-breakup. The delay of U is attributed to the thermospheric inertia. During this transition interval, U.V was negative, which would result in more efficient generation of frictional heating than the positive U.V case. The sign of U.V, which is related to the relative directions of the neutral wind and plasma drift, is important because of its direct impact on ion-neutral energy exchange during collisions. This becomes especially important during substorm events, where rapid plasma velocity changes are common. The sign of U.V may be used as an indicator to find the times and locations where thermospheric inertia plays a role in the energy dissipation process.

DOI： 10.1186/s40623-022-01710-6

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