Faculty Profiles - SHIOKAWA, Kazuo

Papers - SHIOKAWA, Kazuo

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On the Creation, Depletion, and End of Life of Polar Cap Patches Reviewed

Eriksen, NK; Lorentzen, DA; Oksavik, K; Baddeley, L; Hosokawa, K; Shiokawa, K; Bland, E; Paxton, L; Zhang, YL; Mcwilliams, K; Yeoman, T; Themens, DR

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

Ionospheric convection patterns from the Super Dual Auroral Radar Network are used to determine the trajectories, transit times, and decay rates of three polar cap patches from their creation in the dayside polar cap ionosphere to their end of life on the nightside. The first two polar cap patches were created within 12 min of each other and traveled through the dayside convection throat, before entering the nightside auroral oval after 104 and 92 min, respectively. When the patches approached the nightside auroral oval, an intensification in the poleward auroral boundary occurred close to their exit point, followed by a decrease in the transit velocity. The last patch (patch 3) decayed completely within the polar cap and had a lifetime of only 78 min. After a change in drift direction, patch 3 had a radar backscatter power half-life of 4.23 min, which reduced to 1.80 min after a stagnation, indicating a variable decay rate. 28 minutes after the change in direction, and 16 min after coming to a halt within the Clyde River radar field-of-view, patch 3 appeared to reach its end of life. We relate this rapid decay to increased frictional heating, which speeds up the recombination rate. Therefore, we suggest that the slowed patch motion within the polar cap convection pattern is a major factor in determining whether the patch survives as a recognizable density enhancement by the time the flux tubes comprising the initial patch cross into the nightside auroral oval.

DOI： 10.1029/2023JA031739

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Geomagnetic Effect of the Atmospheric Acoustic Resonance Excited by Earthquakes and Volcano Eruptions Reviewed

Surkov, VV; Pilipenko, VA; Shiokawa, K

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 128 ( 10 ) 2023.10

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

An analytical model of the vertical acoustic resonance between the thermosphere and the earth's surface and its geomagnetic effect has been constructed. Resonance with a frequency of several mHz occurs when an atmospheric acoustic wave (AW) is excited by vibrations of the earth or ocean surface. The derived analytical relationships give a possibility to examine the dependence of the fundamental resonant frequency on the height of the reflecting atmospheric layer and horizontal AW number. Geomagnetic disturbances caused by the impact of AW on the ionosphere are calculated within the framework of a multi-layered model of the ground-atmosphere-ionosphere system. The E-layer of the ionosphere is treated in the approximation of a thin layer with an inclined geomagnetic field, while the topside ionosphere is assumed to consist of a cold collisionless plasma. The dependence of the spectral power of magnetic perturbations on the direction of the horizontal AW propagation is examined. The magnetic perturbation spectra are shown to have maxima at frequencies close to the acoustic resonance frequency. The spectral powers of magnetic perturbations and barometric variations measured during the Iwate-Miyagi Nairik earthquake are in accordance with the model predictions for realistic media and AW parameters. Field-aligned currents that arise when AWs enter the ionospheric E-layer is shown to carry measurable electromagnetic disturbances into the geomagnetically conjugated region.

DOI： 10.1029/2023JA031872

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Correspondence of Pi2 pulsations, aurora luminosity, and plasma flux fluctuation near a substorm brightening aurora: Arase observations Reviewed

L. Chen, K. Shiokawa, Y. Miyoshi, S. Oyama, C‐W. Jun, Y. Ogawa, K. Hosokawa, Y. Kazama, S. Y. Wang, S. W. Y. Tam, T. F. Chang, B. J. Wang, K. Asamura, S. Kasahara, S. Yokota, T. Hori, K. Keika, Y. Kasaba, A. Kumamoto, F. Tsuchiya, M. Shoji, Y. Kasahara, A. Matsuoka, I. Shinohara, S. Nakamura

Journal of Geophysical Research: Space Physics 2023.9

Language：English Publishing type：Research paper (scientific journal) Publisher：American Geophysical Union (AGU)

Abstract

Although many substorm‐related observations have been made, we still have limited insight into propagation of the plasma and field perturbations in Pi2 frequencies (∼7‐25 mHz) in association with substorm aurora, particularly from the auroral source region in the inner magnetosphere to the ground. In this study, we present conjugate observations of a substorm brightening aurora using an all‐sky camera and an inner‐magnetospheric satellite Arase at L ∼ 5. A camera at Gakona (62.39<sup>o</sup>N, 214.78<sup>o</sup>E), Alaska, observed a substorm auroral brightening on December 28, 2018, and the footprint of the satellite was located just equatorward of the aurora. Around the timing of the auroral brightening, the satellite observed a series of quasi‐periodic variations in the electric and magnetic fields and in the energy flux of electrons and ions. We demonstrate that the diamagnetic variations of thermal pressure and medium‐energy ion energy flux in the inner magnetosphere show approximately one‐to‐one correspondence with the oscillations in luminosity of the substorm brightening aurora and high‐latitudinal Pi2 pulsations on the ground. We also found their anti‐correlation with low‐energy electrons. Cavity‐type Pi2 pulsations were observed at mid‐ and low‐latitudinal stations. Based on these observations, we suggest that a wave phenomenon in the substorm auroral source region, like ballooning type instability, play an important role in the development of substorm and related auroral brightening and high‐latitude Pi2, and that the variation of the auroral luminosity was directly driven by keV electrons which were modulated by Alfven waves in the inner magnetosphere.

DOI： 10.1029/2023ja031648

A machine learning approach for total electron content (TEC) prediction over the northern anomaly crest region in Egypt Reviewed

Rukundo W., Shiokawa K., Elsaid A., AbuElezz O.A., Mahrous A.M.

Advances in Space Research Vol. 72 ( 3 ) page： 790 - 804 2023.8

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

In this paper, we developed an empirical model for predicting Total Electron Content (TEC) on a single station receiver located within the equatorial anomaly crest region at Helwan – Egypt (29.86°N, 31.32°E & MLAT 27.02°N). The neural network algorithm was developed from several inputs representing diurnal, seasonal, and solar cycle variations, solar and geomagnetic activity, and solar wind parameters using TEC data collected by the SCINDA GPS receiver. The TEC data collected for about nine years from 2009 to 2017 comprises almost the whole solar cycle 24 allowing the developed model to be validated and tested for different solar activity conditions. The 2009 – 2016 dataset was randomly divided into 70% for training, and 30% for validation during model development while the 2017 dataset was reserved for testing the model during independent validation. The validation was done by comparing TEC from the developed model and TEC derived from the GPS scintillation and TEC monitor (GPSTEC). Knowing that TEC modeling over the equatorial anomaly crest regions is challenging since it is characterized by high temporal and spatial variations, the developed model reconstructed diurnal GPSTEC from 2014 to 2016 with a root mean square error (RMSE) of 4.0 TECU and 3.2 TECU for high and low solar activity phases respectively. The neural network (NN) modeled TEC was highly correlated with GPSTEC, that is 0.93 and 0.94 for low and high solar activity respectively. In comparison, the International Reference Ionosphere (IRI)-2016 model predicted the general trend of GPSTEC in 2017 with RMSE of 5.43 TECU better than the developed TEC model with RMSE of 5.74 TECU. However, the NN model predicted diurnal GPSTEC for selected quiet and disturbed days, and seasonal TEC better than the IRI model in 2017. Therefore, the developed model was able to capture temporal ionospheric TEC for diurnal and seasonal variations during low solar activity. It was established that the performance of the empirical model depends on the size and distribution of the data used for model development. It's worth noting that despite the improved performance of the NN algorithm in predicting diurnal and seasonal TEC variation, the NN-modeled TEC performed poorly in reconstructing the nighttime anomalies exhibited in the GPSTEC. The inclusion of the IRI-NmF2 as network input also adds to the improved performance of the network.

DOI： 10.1016/j.asr.2022.10.052

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A Ground‐Based Instrument Suite for Integrated High‐Time Resolution Measurements of Pulsating Aurora With Arase Reviewed

K. Hosokawa, S.‐I. Oyama, Y. Ogawa, Y. Miyoshi, S. Kurita, M. Teramoto, S. Nozawa, T. Kawabata, Y. Kawamura, Y.‐M. Tanaka, H. Miyaoka, R. Kataoka, K. Shiokawa, U. Brändström, E. Turunen, T. Raita, M. G. Johnsen, C. Hall, D. Hampton, Y. Ebihara, Y. Kasahara, S. Matsuda, I. Shinohara, R. Fujii

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

Equatorial plasma bubble intensities across longitudinal sectors of the globe using GNSS observations Reviewed

Okoh Daniel, Shiokawa Kazuo, Otsuka Yuichi, Rabiu Babatunde, Habarulema John Bosco, Migoya-Orue Yenca, Cesaroni Claudio

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 249 2023.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Atmospheric and Solar-Terrestrial Physics

We present the first investigation of Equatorial Plasma Bubble (EPB) intensities across longitudinal sectors of the globe using observations from global navigation satellite system (GNSS) receivers. GNSS data from a total of 93 receiver stations located within ±20 degrees of the geomagnetic equator across the globe were used. The data covered periods of years 2014 and 2019 which are respectively years of high and low solar activity in solar cycle 24. We define a parameter known as the Standard deviation of Residual TEC (SRT) to characterize the EPB intensities. The EPB occurrence was defined by day-night differences of the rate of change of TEC index (ROTI). We observed a high correlation (r ∼ 0.80) between the magnitudes of the SRT and ROTI during the EPB occurrence, but the correlation is low (r ∼ 0.37) during non occurrence of EPB. The EPB intensities are greater during seasons with high occurrence rates. The EPB intensities and occurrence rates are also greater during the high solar activity. We found that the post-sunset intensities are greatest in the Atlantic region, followed by the African region, then the American, Australian, Asian, and Pacific regions in that order. The post-midnight intensities are greatest in the African region, followed by the Atlantic, American, Australian, Asian, and Pacific regions in that order.

DOI： 10.1016/j.jastp.2023.106097

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

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

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Statistical Analysis of the Horizontal Phase Velocity Distribution of Atmospheric Gravity Waves and Medium-Scale Traveling Ionospheric Disturbances in Airglow Images Over Darwin (12.4 degrees S, 131.0 degrees E) Reviewed

Tsuboi Takuma, Shiokawa Kazuo, Otsuka Yuichi, Fujinami Hatsuki, Nakamura Takuji, Neudegg David

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 128 ( 8 ) 2023.8

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

Atmospheric gravity waves (AGWs) and medium-scale traveling ionospheric disturbances (MSTIDs) in the upper atmosphere can be observed in nocturnal airglow images. Spectral analysis of airglow images provides propagation direction and intensity of these waves. However, the spectral analysis of airglow images has not been done yet for stations in the southern hemisphere except for Antarctica. In this study, we calculated the horizontal phase velocity spectra of AGWs in the mesosphere-lower-thermosphere (MLT) region near the mesopause and MSTIDs in the F-region ionosphere from airglow images at wavelengths of 557.7 and 630.0 nm, respectively, by applying the 3-dimensional Fourier spectral analysis to the airglow images obtained at Darwin (12.4°S, 131.0°E) in Australia for 13.75 years from 2001 to 2007 and from 2011 to 2019. The spectra of AGWs in the MLT region show clear characteristics that the southward power spectral density (PSD) is stronger in summer and weaker in winter. Tropospheric convection was located at north of Darwin in summer and above Darwin in winter, suggesting that the tropospheric convection is a possible source of AGWs in the mesopause region. The spectra of MSTIDs in the F-region ionosphere show that the dominant northwestward PSD is stronger in winter and during solar quiet periods. These features can be explained if the observed MSTIDs are caused by the ionospheric instabilities. A weak positive correlation was observed between PSDs of AGWs in the mesosphere and MSTIDs. We propose that the MSTIDs propagating other than northwestward may be generated by AGWs.

DOI： 10.1029/2022JA030769

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

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

Interhemispheric Coupling Study by Observations and Modelling (ICSOM): Concept, Campaigns, and Initial Results Reviewed

Kaoru Sato, Yoshihiro Tomikawa, Masashi Kohma, Ryosuke Yasui, Dai Koshin, Haruka Okui, Shingo Watanabe, Kazuyuki Miyazaki, Masaki Tsutsumi, Damian Murphy, Chris Meek, Yufang Tian, Manfred Ern, Gerd Baumgarten, Jorge L. Chau, Xinzhao Chu, Richard Collins, Patrick J. Espy, Hiroyuki Hashiguchi, Andrew J. Kavanagh, Ralph Latteck, Franz‐Josef Lübken, Marco Milla, Satonori Nozawa, Yasunobu Ogawa, Kazuo Shiokawa, M. Joan Alexander, Takuji Nakamura, William E. Ward

Journal of Geophysical Research: Atmospheres Vol. 128 ( 11 ) 2023.6

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

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) Publisher：Springer Science and Business Media LLC

Abstract

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

DOI： 10.1186/s40623-023-01829-0

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Other Link： https://link.springer.com/article/10.1186/s40623-023-01829-0/fulltext.html

Unsolved problems: Mesoscale polar cap flow channels' structure, propagation, and effects on space weather disturbances Reviewed

Lyons Larry. R. R., Nishimura Yukitoshi, Liu Jiang, Zou Ying, Bristow William. A. A., Yadav Sneha, Donovan Eric, Nishitani Nozomu, Shiokawa Kazuo, Hosokawa Keisuke

FRONTIERS IN ASTRONOMY AND SPACE SCIENCES Vol. 10 2023.4

Multi-Event Conjugate Measurements of the SAR Arc Detachment From the Auroral Oval Using DMSP Satellites and an All-Sky Camera at Athabasca, Canada Reviewed

Gololobov A., Shiokawa K., Baishev D., Inaba Y., Otsuka Y., Connors M.

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 report the first statistical study of stable auroral red (SAR) arcs detached from the main auroral oval during non-storm time, using multi-event conjugate measurements by the Defense Meteorological Satellite Program (DMSP) satellites (F13–F19) and a ground-based all-sky imager at Athabasca (Canada) (54.6°W, 246.36°Е, MLAT = 61.5°, MLON = 308.3°, L = 4.4). We found 63 events of detached SAR arc conjunctions with the DMSP satellites in the northern hemisphere and 18 events in the opposite southern hemisphere from 2006 to 2018. Measurements aboard DMSP satellites show that detached SAR arcs are in general associated with enhancements of electron temperature (60 cases) and electron density troughs (58 cases). Only 14 cases show strong horizontal flow associated with the detached SAR arcs, indicating that the strong plasma flow is not a necessary condition to cause the detached SAR arcs. The electron temperature measured by DMSP associated with detached SAR arcs positively correlates with F10.7 solar activity index. The measured emission intensities at 630.0 nm in the SAR arcs show a good correlation with the electron temperature. These results indicate that the detached SAR arcs during non-storm time are caused by heat flux from the magnetosphere associated with substorms, and their intensity depends on the background plasma condition in the ionosphere.

DOI： 10.1029/2022JA030544

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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

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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A Statistical Study of Longitudinal Extent of Pc1 Pulsations Using Seven PWING Ground Stations at Subauroral Latitudes Reviewed

Jie Liu, Kazuo Shiokawa, Shin‐Ichiro Oyama, Yuichi Otsuka, Chae‐Woo Jun, Masahito Nosé, Tsutomu Nagatsuma, Kaori Sakaguchi, Akira Kadokura, Mitsunori Ozaki, Martin Connors, Dmitry Baishev, Nozomu Nishitani, Alexey Oinats, Vladimir Kurkin, Tero Raita

Journal of Geophysical Research: Space Physics Vol. 128 ( 1 ) 2023.1

Ionospheric Modulation by EMIC Wave-Driven Proton Precipitation: Observations and Simulations Reviewed Open Access

Tian, XB; Yu, YQ; Gong, F; Ma, LX; Cao, JB; Solomon, SC; Shreedevi, PR; Shiokawa, K; Otsuka, Y; Oyama, S; Miyoshi, Y

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 128 ( 1 ) 2023.1

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

Protons of tens of keV can be resonantly scattered by electromagnetic ion cyclotron (EMIC) waves excited in the magnetosphere, resulting in proton precipitation down to the upper atmosphere. In this study, we report for the first time the ionospheric height-dependent ionization in response to EMIC-associated isolated proton aurora (IPA) using simultaneous space-borne and ground-based measurements. On 06 March 2019, the Polar Orbiting Environmental Satellites observed significant proton precipitation in the dusk sector (MLT ∼ 19), while ground-based magnetometers detected a clear signature of EMIC waves. Meanwhile, the conjugated all sky imager captured an IPA and the nearby Poker Flat incoherent scatter radar (PFISR) showed enhanced electron density in the E region, suggesting a potential consequence of the EMIC wave-driven proton precipitation. The Global Airglow model simulations confirmed the dominant impact of proton precipitation on the ionosphere and agreed well with PFISR observations. This study confirmed physical links from the magnetosphere to the ionosphere through EMIC-driven proton precipitation.

DOI： 10.1029/2022JA030983

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ELECTROMAGNETIC ULF/ELF OSCILLATIONS CAUSED BY THE ERUPTION OF THE TONGA VOLCANO Reviewed

Martines-Bedenko V. A., Pilipenko V. A., Shiokawa K., Akbashev R. R.

SOLAR-TERRESTRIAL PHYSICS Vol. 9 ( 1 ) page： 47 - 55 2023

Language：English Publishing type：Research paper (scientific journal) Publisher：Solar-Terrestrial Physics

The eruption of the Tonga volcano on January 13 and 15, 2022 and related intense lightning activity led to the excitation of a number of specific electromagnetic oscillations in different frequency ranges. We examine properties of these oscillations, using data from magnetometers of various types located in Kamchatka and in the Pacific region. We confirmed that there might have been a geomagnetic response to the formation of an acoustic resonance between the Earth surface and the ionosphere: localized harmonic oscillations with a frequency 3.5-4.0 mHz, which lasted for ~1.5 hr, were detected ~15 min after the beginning of the eruption at distance of ~800 km. An increase was observed in the intensity of the Schumann resonance at stations in the Far East. Broadband emission stimulated by intense volcanic lightning was detected to occur in the Pc1 range (2-5 Hz). The emission presumably results from the excitation of the magnetosonic waveguide in the upper ionosphere by lightning activity.

DOI： 10.12737/stp-91202306

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SEARCH FOR PULSED ULTRALOW-FREQUENCY ELECTROMAGNETIC EARTHQUAKE PRECURSORS Reviewed Open Access

Martines-Bedenko V.A., Pilipenko V.A., Shiokawa K., Kasimova V.A.

Geophysical Research Vol. 24 ( 2 ) page： 5 - 24 2023

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

Numerous publications have appeared in the literature describing a new seismo-electromagnetic effect – the appearance of magnetic pulses with a duration of 1–40 s, which are detected at distances up to ten thousand km several minutes before earthquakes of even low magnitude. An assumption was made about the universality of the processes of impulse precursor generation and the fundamental possibility of a short-term (several minutes) warning of an approaching earthquake. In the presented article, the possibility of the appearance of ultra-low-frequency pulses that precede seismic events with magnitudes M>5.0, according to the data of a network of induction magnetometers in the Far East, is investigated. In the records of these highly sensitive magnetometers, impulse disturbances are constantly encountered, some of which are observed synchronously at several stations, which eliminates the influence of local noise. The spectral maximum of about 7–8 Hz of the oscillatory structure, which manifests itself in many pulses, corresponds to the fundamental frequency of the Schumann resonator. A comparison of magnetic observations with data from the WWLLN (World Wide Lightning Location Network) showed that some of the pulses were caused by lightning discharges in the 650 km vicinity of magnetic station. Despite the fact that some of the impulses are observed immediately before earthquakes, it is impossible to speak with confidence about their connection with seismic activity. The calculation of the number of impulses in the 5-min interval before and after the seismic shock shows that they are randomly distributed relative to the moment of the earthquake. Apparently, the pulses are predominantly due to the ionospheric response to a far lightning discharge.

DOI： 10.21455/gr2023.2-1

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Ultra Low Frequency Modulation of Energetic Electron Precipitation in the D-Region Ionosphere in a Magnetically Quiet Time Using OCTAVE Very Low Frequency and Low Frequency (VLF/LF) Observations Reviewed

Kentaro Tanaka, Hiroyo Ohya, Fuminori Tsuchiya, Kenro Nozaki, Mariko Teramoto, Kazuo Shiokawa, Yoshizumi Miyoshi, Martin Connors, Hiroyuki Nakata

URSI Radio Science Letters Vol. 4 2023

Relationship between geomagnetic storms and occurrence of ionospheric irregularities in the west sector of Africa during the peak of the 24th solar cycle Reviewed

Ondede George Ochieng, Rabiu A. B., Okoh Daniel, Baki Paul, Olwendo Joseph, Shiokawa Kazuo, Otsuka Yuichi

FRONTIERS IN ASTRONOMY AND SPACE SCIENCES Vol. 9 2022.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Frontiers in Astronomy and Space Sciences

The study of ionospheric irregularities is important since many technological systems might be influenced by the ionosphere. In this work, we use data from the Global Navigation Satellite Systems (GNSS) receiver installed in Abuja, Nigeria, GPS Scintillation Network Decision Aid (SCINDA) TEC data from the Air Force Research Laboratory (AFRL) data archive, and the geomagnetic data from the World Data Center (WDC) in Kyoto, Japan, to investigate the relationship between geomagnetic storm and ionospheric irregularity occurrences using the rate of change of total electron content (TEC) index (ROTI), with a validation using the S4 indices, during the peak of the 24th solar cycle. The occurrences of irregularities were investigated on day-to-day and seasonal bases. The nighttime ionospheric irregularities, which are attributed to ionospheric plasma irregularities in the equatorial ionospheric F-region, were found to be prevalent. To investigate the relationship between the strength of ionospheric irregularities (ROTI) and the geomagnetic storm (Dst), the periodogram power spectral density (PSD) and regression analysis were used. The results showed that there was no correlation, cc = 0.073, between the Dst and ROTI, implying that the strengths of ionospheric irregularities occurring during geomagnetic storms are not strictly decided by the magnitudes of the storms; this was also confirmed using the S4 index. The impact of geomagnetic storms caused enhanced development or inhibition of ionospheric irregularities. We observed that the bulk of the storms occurring during the period of this study is not associated with ionospheric irregularities. Finally, the investigation showed that the correlation between the ROTI and Dst observed during the coronal mass ejection (CME)-driven geomagnetic storms was higher than that during the corotating interaction region (CIR)-driven geomagnetic storms, during the peak of the 24th solar cycle. The results of this work confirm the findings by other researchers.

DOI： 10.3389/fspas.2022.969235

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Papers - SHIOKAWA, Kazuo