Faculty Profiles - SHIOKAWA, Kazuo

Detecting Equatorial Plasma Bubbles on All-Sky Imager Images Using Convolutional Neural Network Reviewed

Statistical survey of Arase satellite data sets in conjunction with the Finnish Riometer Network Reviewed Open Access

Neethal Thomas, Antti Kero, Yoshizumi Miyoshi, Kazuo Shiokawa, Miikka Hyötylä, Tero Raita, Yoshiya Kasahara, Iku Shinohara, Shoya Matsuda, Satoko Nakamura, Satoshi Kasahara, Shoichiro Yokota, Kunihiro Keika, Tomoaki Hori, Takefumi Mitani, Takeshi Takashima, Kazushi Asamura, Yoichi Kazama, Shiang‐Yu Wang, C‐W. Jun, Nana Higashio

Journal of Geophysical Research: Space Physics Vol. 127 ( 5 ) 2022.5

Simultaneous Observations of EMIC‐Induced Drifting Electron Holes (EDEHs) in the Earth's Radiation Belt by the Arase Satellite, Van Allen Probes, and THEMIS Reviewed Open Access

S. Nakamura, Y. Miyoshi, K. Shiokawa, Y. Omura, T. Mitani, T. Takashima, N. Higashio, I. Shinohara, T. Hori, S. Imajo, A. Matsuoka, F. Tsuchiya, A. Kumamoto, Y. Kasahara, M. Shoji, H. Spence, V. Angelopoulos

Geophysical Research Letters Vol. 49 ( 5 ) 2022.3

Srisamoodkham W., Shiokawa K., Otsuka Y., Ansari K., Jamjareegulgarn P.

Lecture Notes in Networks and Systems Vol. 461 page： 481 - 487 2022

Language：English Publishing type：Research paper (scientific journal) Publisher：Lecture Notes in Networks and Systems

This paper proposes initially to apply convolutional neural network (CNN) for detecting the equatorial plasma bubbles on the ASI images. The considered CNN model is the YOLO v3 tiny model under a deep learning API (Keras), running on top of the machine learning platform (TensorFlow). Our program for EPB detection is written in Python that is extended easily to combine into a space weather web site for detecting and notifying EPBs in our next step. The results show that the YOLO v3-based CNN can detect the EPBs in ASI images with different intensities obtained from many countries. The threshold is tested and selected to be 0.40 suitably for detecting the anomaly (EPB existence). The maximum anomalous value is selected to decide the EPB occurrence.

DOI： 10.1007/978-981-19-2130-8_38

Spatio-Temporal Distributions of Lightning Stroke Charge Using ELF and Meteorological Data Reviewed

Variations of Zonal Wind Velocity in the Thermosphere Observed at Southeast Asian Sector During Quiet and Active Geomagnetic Days Reviewed

Sarudin Idahwati, Hamid Nurul Shayana Abdul, Abdullah Mardina, Rusli Fatin Nur Syakirah Mohd, Otsuka Yuichi, Shiokawa Kazuo, Yatini Clara, Komonjinda Siramas, Somboon Ekkarach

JURNAL FIZIK MALAYSIA Vol. 43 ( 1 ) page： 10025 - 10035 2022

Yasuhide Hobara, Takuhiko Ohashi, Tomonori Shiraishi, Kazuo Shiokawa

Lecture Notes in Electrical Engineering Vol. 842 page： 329 - 337 2022

Language：English Publishing type：Research paper (international conference proceedings)

In this paper lightning stroke charges are estimated remotely by using combinations of Extremely Low Frequency (ELF) radio waves, conventional Lightning Locating System (LLS) and local meteorological information for the first time. Each lightning stroke location from LLS and corresponding transient signature of ELF magnetic field observed at a long distance (−1000 km between lightning stroke and observation site) are utilized to estimate the charge moment change (CMC) of the lightning stroke. The lightning stroke charge Q is then derived by dividing the CMC by the altitude of the neutralized lightning charge. The corresponding altitude of the neutralized lightning charge for each stroke is determined by assuming local −20 °C altitude for a positive stroke (−10 °C altitude for a negative strokes) from MesoScale Model (MSM). Spatial and temporal frequency distributions of energetic lightning (large amount of stroke charge) and cumulative frequency distributions of stroke charge in northwestern part of Japan in local summer and winter seasons for 4 years were derived. The spatial occurrence frequency distributions indicate that lightning strokes with a large amount of neutralized charge occur more frequently in inland areas during summertime and in coastal areas in winter. The cumulative frequency distribution indicates that positive polarity lightning strokes in winter tend to have a large charge. Our statistical results are in good agreement with the lightning properties inferred from local observations, and are considered to be useful information not only to study electrical properties of thunderstorms but also for future maintenance planning of power grid systems in wide areas and mitigation of lightning damages.

DOI： 10.1007/978-981-16-8690-0_30

RESPONSE OF THE D-REGION IONOSPHERE TO FIREBALLS USING VLF/LF TRANSMITTER SIGNALS Reviewed Open Access

Takeru Suzuki, Hiroyo Ohya, Fuminori Tsuchiya, Kazuo Shiokawa, Hiroyuki Nakata

18th Annual Meeting of the Asia Oceania Geosciences Society page： 215 - 217 2022

Horizontal Inhomogeneity in the D-Region Ionosphere During an X-Class Solar Flare Determined by OCTAVE VLF Observations Reviewed

Masaharu Nakayama, Hiroyo Ohya, Fuminori Tsuchiya, Kenro Nozaki, Kazuo Shiokawa, Hiroyuki Nakata

URSI Radio Science Letters Vol. 4 2022

Spatio-Temporal Characteristics of Energetic Lightning in Southeast Asia: Preliminary Statistical Results Reviewed

Shunsuke Akama, Yasuhide Hobara, Amir Izzani Mohamed, Chandima Gomes, Kazuo Shiokawa, Shu Hirai, Hiroshi Kikuchi, Michael Stock

Lecture Notes in Electrical Engineering Vol. 842 page： 317 - 327 2022

Language：English Publishing type：Research paper (international conference proceedings)

The region of Southeast Asia is known as one of the lightning-prone areas in the world. However, spatial and temporal distributions of high-energy lightning discharges, which cause natural disasters e.g. significant damages to local power grid systems and forest fires, are still unknown. This paper reports initial results on the statistical characteristics of energetic lightning around Malay Peninsula. Highly accurate timing and location as well as lightning peak current (Ip ) of lightning strokes were obtained by ENTLN (Earth Networks Total Lightning Network), while the vertical charge moment change Qds as a proxy of high-energy lightning was derived by using ground-based ELF magnetic field observations in Pahang, Malaysia with a small threshold of less than 10 C·km. The characteristics of energetic lightning for both rainy and dry seasons were successfully derived for the first time in this region. The results indicate that highly energetic lightning occur frequently throughout the rainy and dry seasons, mainly over the Malacca Strait. Long-term statistical analysis with an extended data analysis period is necessary to understand further the seasonal and yearly dependences of energetic lightning and their relations with local climate conditions.

DOI： 10.1007/978-981-16-8690-0_29

Predictability of variable solar-terrestrial coupling Reviewed Open Access

Daglis Ioannis A., Chang Loren C., Dasso Sergio, Gopalswamy Nat, Khabarova Olga V, Kilpua Emilia, Lopez Ramon, Marsh Daniel, Matthes Katja, Nandy Dibyendu, Seppala Annika, Shiokawa Kazuo, Thieblemont Remi, Zong Qiugang

ANNALES GEOPHYSICAE Vol. 39 ( 6 ) page： 1013 - 1035 2021.12

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

In October 2017, the Scientific Committee on Solar-Terrestrial Physics (SCOSTEP) Bureau established a committee for the design of SCOSTEP's Next Scientific Programme (NSP). The NSP committee members and authors of this paper decided from the very beginning of their deliberations that the predictability of the Sun-Earth System from a few hours to centuries is a timely scientific topic, combining the interests of different topical communities in a relevant way. Accordingly, the NSP was christened PRESTO -PREdictability of the variable Solar-Terrestrial cOupling. This paper presents a detailed account of PRESTO; we show the key milestones of the PRESTO roadmap for the next 5 years, review the current state of the art and discuss future studies required for the most effective development of solar-terrestrial physics.

DOI： 10.5194/angeo-39-1013-2021

Auroral Heating of Plasma Patches Due to High-Latitude Reconnection Reviewed

Pena Joaquin Diaz, Semeter Joshua, Nishimura Yukitoshi, Varney Roger, Reimer Ashton, Hairston Marc, Zettergren Matthew, Hirsch Michael, Verkhoglyadova Olga, Hosokawa Keisuke, Shiokawa Kazuo

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 126 ( 12 ) 2021.12

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

This study exploits the volumetric sampling capabilities of the Resolute Bay Incoherent Scatter Radar (RISR-N) in collaboration with all-sky imagery and in situ measurements to examine the interplay between cold plasma transport and auroral precipitation during a high-latitude lobe reconnection event on the dawn side. Solar wind IMF preceding the event was characterized by an impulsive negative excursion in Bz embedded within a period of Bz > 0 and By < 0. The combined effects of transport and magnetic stress release associated with a high-latitude reconnection pulse drove a co-mingling between patches and soft electron precipitation, creating common regions of elevated electron density and temperature. Vertical ionospheric profiles extracted in the rest frame of the drifting patch showed a contemporaneous increase in Te above 200 km and Ne below 250 km while at the same time showing only a small impact in Ne near the F-region peak. The observations suggest a new mechanism for creating a “hot patch” wherein the density enhancement is not generated by the precipitation but is warmed by it. The physics-based GEMINI model was used to explore the response to the observed precipitation as a function of altitude and time. Model results suggest that a correlated enhancement in Ne and Te at DMSP altitudes (∼800 km), that is, hot patch, can be produced by auroral heating and upward diffusion, irrespective of lower altitude density structure. The study highlights the need for densely distributed observations in space and time for understanding both mesoscale and small-scale ionospheric dynamics in regions subject to complex forcing.

DOI： 10.1029/2021JA029657

Periodicities and Colors of Pulsating Auroras: DSLR Camera Observations From the International Space Station Reviewed

Study of an Equatorward Detachment of Auroral Arc From the Oval Using Ground‐Space Observations and the BATS‐R‐US–CIMI Model Reviewed Open Access

Sneha Yadav, K. Shiokawa, S. Oyama, Y. Inaba, N. Takahashi, K. Seki, K. Keika, Tzu‐Fang Chang, S. W. Y. Tam, B.‐J. Wang, Y. Kazama, S.‐Y. Wang, K. Asamura, S. Kasahara, S. Yokota, T. Hori, Y. Kasaba, F. Tsuchiya, A. Kumamoto, M. Shoji, Y. Kasahara, A. Matsuoka, S. Matsuda, C.‐W. Jun, S. Imajo, Y. Miyoshi, I. Shinohara

Journal of Geophysical Research: Space Physics Vol. 126 ( 12 ) 2021.12

Multipoint Measurement of Fine‐Structured EMIC Waves by Arase, Van Allen Probe A, and Ground Stations Reviewed Open Access

S. Matsuda, Y. Miyoshi, Y. Kasahara, L. Blum, C. Colpitts, K. Asamura, Y. Kasaba, A. Matsuoka, F. Tsuchiya, A. Kumamoto, M. Teramoto, S. Nakamura, M. Kitahara, I. Shinohara, G. Reeves, H. Spence, K. Shiokawa, T. Nagatsuma, S. Oyama, I. R. Mann

Geophysical Research Letters Vol. 48 ( 23 ) 2021.11

Nanjo Sota, Hozumi Yuta, Hosokawa Keisuke, Kataoka Ryuho, Miyoshi Yoshizumi, Oyama Shin-ichiro, Ozaki Mitsunori, Shiokawa Kazuo, Kurita Satoshi

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 126 ( 10 ) 2021.10

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

We investigated the spatial characteristics of pulsating auroras (PsA) using digital camera measurements from the International Space Station. These measurements covered PsAs in (Formula presented.) 5-h wide regions in the magnetic local time (MLT) direction in short time intervals ((Formula presented.) 10 min). Analyses of two events suggested that the periodicity of the main pulsation of a PsA does not exhibit any clear dependence on the magnetic latitude (63– (Formula presented.)) and MLT (00–05). These results suggest that the periods are not controlled by the bounce time of trapped electrons but by local conditions such as gradients of temperature and/or density of electrons near the magnetospheric source region. We also analyzed the colors of PsAs as proxies for the energies of precipitating electrons. The blue and green channels of the digital camera are sensitive to the band emission of molecular nitrogen ions and the green line of oxygen atoms, respectively. Because the energy bands of precipitating electrons producing those two emissions are different, ratios of blue to green (B/G ratios) can be used as proxies for the energies of PsA electrons. The B/G ratio tends to be higher in the morning sector than in the midnight sector, which is consistent with the results of previous studies showing the MLT dependence of the energies of PsA electrons. This capability of estimating the energies of auroral electrons from digital camera images is expected to provide more opportunities for citizen scientists to contribute more deeply to auroral science.

DOI： 10.1029/2021JA029564

Isolated Proton Aurora Driven by EMIC Pc1 Wave: PWING, Swarm, and NOAA POES Multi-Instrument Observations Reviewed Open Access

Hyangpyo Kim, Kazuo Shiokawa, Jaeheung Park, Yoshizumi Miyoshi, Yukinaga Miyashita, Claudia Stolle, Hyunju Kim Connor, Junga Hwang, Stephan Buchert, Hyuck Jin Kwon, Satoko Nakamura, Kohki Nakamura, Shin Ichiro Oyama, Yuichi Otsuka, Tsutomu Nagatsuma, Kaori Sakaguchi

Geophysical Research Letters Vol. 48 ( 18 ) 2021.9

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

We report the concurrent observations of F-region plasma changes and field-aligned currents (FACs) above isolated proton auroras (IPAs) associated with electromagnetic ion cyclotron Pc1 waves. Key events on March 19, 2020 and September 12, 2018 show that ground magnetometers and all-sky imagers detected concurrent Pc1 wave and IPA, during which NOAA POES observed precipitating energetic protons. In the ionospheric F-layer above the IPA zone, the Swarm satellites observed transverse Pc1 waves, which span wider latitudes than IPA. Around IPA, Swarm also detected the bipolar FAC and localized plasma density enhancement, which is occasionally surrounded by wide/shallow depletion. This indicates that wave-induced proton precipitation contributes to the energy transfer from the magnetosphere to the ionosphere.

DOI： 10.1029/2021GL095090

An experimental investigation into the possible connections between the zonal neutral wind speeds and equatorial plasma bubble drift velocities over the African equatorial region Reviewed Open Access

Okoh D. I, Rabiu A. B., Shiokawa K., Otsuka Y., Wu Q., Seemala G. K., Katamzi-Joseph Z. T.

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 220 2021.9

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

There is increasing interest to understand thermospheric neutral wind and ionized plasma coupling, especially by using empirical observations. This is the first study that reports simultaneous measurements of thermospheric neutral wind and equatorial plasma bubble (EPB) speeds over the African equatorial region. Neutral wind speeds were obtained using a Fabry-Perot interferometer (FPI), while EPB speeds were obtained using an all-sky optical imager. Both instruments are co-located in Abuja (Geographic: 8.99°N, 7.38°E; Geomagnetic: 1.60°S). Data for 11 nights of coincident neutral wind and EPB speed observations were used. The neutral wind speeds were in the range of about −30 to 300 m/s, while EPB speeds were in the range of about 15–400 m/s. The speeds of both neutral winds and EPBs were generally observed to be faster during the early night hours and to slow down towards midnight. In some instances, the neutral wind and EPB speeds were comparable, an observation that is in agreement with full development of the F region dynamo. There were also instances in which the EPBs were faster or slower than the neutral winds. In one of the nights, a southward turning of the IMF-Bz was observed to cause a sudden increase in the EPB speed. For some nights, the neutral winds were faster than the EPBs during earlier hours of the nights, and the disparity reduced during the later hours of the nights. This was attributed to the possibility that the F region dynamo was yet to be fully developed during the earlier hours.

DOI： 10.1016/j.jastp.2021.105663

First Simultaneous Observation of a Night Time Medium‐Scale Traveling Ionospheric Disturbance From the Ground and a Magnetospheric Satellite Reviewed Open Access

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

Journal of Geophysical Research: Space Physics Vol. 126 ( 9 ) 2021.9

Multi-instrument study of longitudinal wave structures for plasma bubble seeding in the equatorial ionosphere Reviewed Open Access

Takahashi H., Essien P., Figueiredo C. A. O. B., Wrasse C. M., Barros D., Abdu M. A., Otsuka Y., Shiokawa K., Li GuoZhu

EARTH AND PLANETARY PHYSICS Vol. 5 ( 5 ) page： 368 - 377 2021.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Earth and Planetary Physics

Large Scale Wave Structures (LSWS) in the equatorial ionospheric F-region were observed by measuring spatial and temporal variations within detrended total electron content (dTEC) data obtained by ground-based GNSS receivers over the South American continent. By using dTEC-maps, we have been able to produce, for the first-time, two-dimensional representations of LSWS. During the period from September to December, the LSWS frequently occurred starting a few hours prior to Equatorial Plasma Bubble (EPB) development. From 17 events of LSWS observed in 2014 and 2015, wave characteristics were obtained: the observed wavelengths, periods, and the phase speeds are respectively, ~900 km, ~41 min and ~399 m/s; the waves propagated from the northeast to southeast. In some cases the front of the oscillation was meridionally aligned, extending to more than 1600 km, the first time such large extension of the wavefront has been reported. From F-layer bottom height oscillation data, measured by ionosonde, LSWS exhibit two different vertical phase propagation modes, in-phase and downward phase. The former mode indicates the presence of a polarization electric field in the F-layer bottom side; the latter suggests propagation of atmospheric gravity waves. The presence of LSWS near the solar terminator, followed by the development of EPBs, suggests that the upwelling of the F-layer bottom height produces a condition favorable to the development of Rayleigh–Taylor instability.

DOI： 10.26464/epp2021047

PSTEP: project for solar-terrestrial environment prediction Reviewed International journal Open Access

Kanya Kusano, Kiyoshi Ichimoto, Mamoru Ishii, Yoshizumi Miyoshi, Shigeo Yoden, Hideharu Akiyoshi, Ayumi Asai, Yusuke Ebihara, Hitoshi Fujiwara, Tada-Nori Goto, Yoichiro Hanaoka, Hisashi Hayakawa, Keisuke Hosokawa, Hideyuki Hotta, Kornyanat Hozumi, Shinsuke Imada, Kazumasa Iwai, Toshihiko Iyemori, Hidekatsu Jin, Ryuho Kataoka, Yuto Katoh, Takashi Kikuchi, Yuki Kubo, Satoshi Kurita, Haruhisa Matsumoto, Takefumi Mitani, Hiroko Miyahara, Yasunobu Miyoshi, Tsutomu Nagatsuma, Aoi Nakamizo, Satoko Nakamura, Hiroyuki Nakata, Naoto Nishizuka, Yuichi Otsuka, Shinji Saito, Susumu Saito, Takashi Sakurai, Tatsuhiko Sato, Toshifumi Shimizu, Hiroyuki Shinagawa, Kazuo Shiokawa, Daikou Shiota, Takeshi Takashima, Chihiro Tao, Shin Toriumi, Satoru Ueno, Kyoko Watanabe, Shinichi Watari, Seiji Yashiro, Kohei Yoshida, Akimasa Yoshikawa

EARTH PLANETS AND SPACE Vol. 73 ( 1 ) 2021.8

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

Although solar activity may significantly impact the global environment and socioeconomic systems, the mechanisms for solar eruptions and the subsequent processes have not yet been fully understood. Thus, modern society supported by advanced information systems is at risk from severe space weather disturbances. Project for solar-terrestrial environment prediction (PSTEP) was launched to improve this situation through synergy between basic science research and operational forecast. The PSTEP is a nationwide research collaboration in Japan and was conducted from April 2015 to March 2020, supported by a Grant-in-Aid for Scientific Research on Innovative Areas from the Ministry of Education, Culture, Sports, Science and Technology of Japan. By this project, we sought to answer the fundamental questions concerning the solar-terrestrial environment and aimed to build a next-generation space weather forecast system to prepare for severe space weather disasters. The PSTEP consists of four research groups and proposal-based research units. It has made a significant progress in space weather research and operational forecasts, publishing over 500 refereed journal papers and organizing four international symposiums, various workshops and seminars, and summer school for graduate students at Rikubetsu in 2017. This paper is a summary report of the PSTEP and describes the major research achievements it produced.

DOI： 10.1186/s40623-021-01486-1