Solar-Terrestrial Environment Prediction: Toward the Synergy of Scienceand Forecasting Operation of Space Weather and Space Climate

Editorial Board (May 2023)
Editor-in-Chief

Takeshi Sagiya, Nagoya University, Japan

Vice Editors-in-Chief

Masahito Nosé, Nagoya City University, Japan

Editors

Koki Aizawa
Hideo Aochi
Pascal Audet
Kiyoshi Baba
Toshitaka Baba
Joseph B.H. Baker
Nanan Balan
Stephan Christoph Buchert
Sonia Calvari
Xiaowei ChenPeter Chi
Kuo-En Ching
Phil Cummins
Hao Dong
Guangyu Fu
Hidenori Genda
Aditya Gusman
Stuart Henrys
Yuji Himematsu

Advisory Board

Benjamin Fong Chao
Bernard Chouet
Yoshimori Honkura
Toshihiko Iyemori

Aitaro Kato, University of Tokyo, Japan

Hauke Hussmann
Mie Ichihara
Hidekatsu Jin
Art Jolly
Shunichi Kamata
Nobuki Kame
Katsuya Kaneko
Ikuo Katayama
Yoko Kebukawa
Kunihiro Keika
Kostas Konstantinou
Alexey Kuvshinov
Juanjo Ledo
Koji Matsuo
Yasunobu Miyoshi
Atsuko Namiki
Yasuhito Narita
Kazunari Nawa
Kiwamu Nishida

Hiroyo Ohya
Duggirala Pallamraju
Severine Rosat
Susumu Saito
David Shelly
Hisayoshi Shimizu
Wataru Suzuki
Youichiro Takada
Sunny Tam
Naoki Uchida
Yanbin Wang
Yih-Min Wu
Takahiro Yamamoto
Yuhji Yamamoto
Yusuke Yokota
Yohei Yukutake
Seiji Zenitani

Hiroo Kanamori
Jun'ichiro Kawaguchi
Takafumi Matsui
Hitoshi Mizutani

Yasuo Ogawa
Toshitaka Tsuda
Zhongliang Wu
Kiyoshi Yomogida

Journal Scope
Earth, Planets and Space (EPS) is the official journal of Society of Geomagnetism and Earth, Planetary
and Space Sciences, The Seismological Society of Japan, The Volcanological Society of Japan, The
Geodetic Society of Japan, and The Japanese Society for Planetary Sciences.
EPS is a peer-reviewed, open-access journal published under SpringerOpen. It is an international journal
covering scientific articles in the entire field of earth and planetary sciences, particularly geomagnetism,aeronomy, space science, seismology, volcanology, geodesy, and planetary science. EPS also welcomesarticles in new and interdisciplinary subjects, and technical reports on instrumentation and software.
The journal was launched in 1998 and has since published over 4000 articles. All of them are available forfree on SpringerLink:
https://link.springer.com/journal/40623/volumes-and-issues
More information about the journal, its article collections, and the submission process is available on thejournal homepage:https://earth-planets-space.springeropen.com
Submit your next research article to Earth, Planets and Space via:
https://www.editorialmanager.com/epsp
Yours sincerely,
Prof. Takeshi Sagiya
Editor-in-Chief, Earth, Planets and Space
eic@earth-planets-space.org

Earth, Planets and Space(2021) 73:198
Kusano et al. Earth, Planets and Space
https://doi.org/10.1186/s40623-021-01530-0

Open Access

PREFACESpecial issue “Solar–terrestrial environment
prediction: toward the synergy of scienceand forecasting operation of space weather
and space climate”
Kanya Kusano1*, Mamoru Ishii2, Tomas Berger3, Yoshizumi Miyoshi1, Shigeo Yoden4, Huixin Liu5,
Terry Onsager6 and Kiyoshi Ichimoto7

Kusano et al. (2021) summarized the major researchachievements of PSTEP about the space weather forecasting system, the prediction of solar storm and geospace
dynamics, solar cycle activity and its climate impact. The
scale of space weather events and their occurrence ratein Japan was surveyed by Ishii et al. (2021), in which theinformation for the space weather disaster defense wasassembled.
One of the major space weather impacts on the society is caused by geomagnetic induced current (GIC).
Watari et al. (2021) overviewed GIC measurement systems and reported several examples of the measurements
in substations around Tokyo, Japan. Yagova et al. (2021)
analyzed GIC in a transformer at the terminal station at
Vykhodnoy, Russia, during the entire year of 2015 andfound that large-scale pulsations are more effective in
GIC generation than small-scale pulsations. Kikuchi et al.
(2021) observed the electromagnetic disturbance causedby the geomagnetic sudden commencement (SC) using
the high-frequency (HF) Doppler sounders at middle andlow latitudes and confirmed that the electric field signal
propagates near-instantaneously (within 10 s) over the
globe.
The evaluation of the influence of energetic particles onsatellites and aircraft is an important task for the space
weather forecast. Nagatsuma et al. (2021) developed theSpace Environment Customized Risk Estimation for Satellites (SECURES) system by combining models of thespace environment and those of spacecraft charging.

The space environmental variability (widely called “space
weather”) can influence the electromagnetic environment
around the earth and human life. In particular, a severe
space weather event caused by a large solar eruption isa potential risk to social infrastructures such as artificial
satellites, aviation, electric power, communications, andpositioning systems. Furthermore, it has been pointed
out that long-term variation in the solar cycle may affect
the global environment. Therefore, predicting the solar–
terrestrial environment is important not only as scientificresearch, but also for sustaining a safe and secure modern society. However, the mechanism of solar–terrestrial
environmental dynamics and its influence on the socioeconomic system is not yet fully understood.
The special issue “Solar–Terrestrial Environment Prediction: Toward the Synergy of Science and Forecasting Operation of Space Weather and Space Climate” is acomprehensive summary of the current status of researchon this issue. In Japan, a nation-wide joint project “theProject for Solar–Terrestrial Environment Prediction(PSTEP)” was conducted from 2015 to 2019 in order toimprove this situation through synergy between the basic
science research and the forecast operation. In this special issue, the various research papers of this project andthe related studies are compiled as follows.
*Correspondence: kusano@nagoya-u.jp
1
Institute for Space-Earth Environmental Research (ISEE), Nagoya
University, Nagoya 464-8601, Japan
Full list of author information is available at the end of the article© The Author(s) 2021. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which
permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to theoriginal author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images orother third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line
to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory
regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of thislicence, visit http://creativecommons.org/licenses/by/4.0/.

1

Solar-Terrestrial Environment Prediction: Toward the Synergy of Science and Forecasting Operation of Space Weather and Space Climate
Kusano et al. Earth, Planets and Space(2021) 73:198

Page 2 of 3

their impact on the global environment. Nishimoto et al.
(2021) examined the computed extreme ultraviolet emission spectra during solar flares. The advanced method for
the CME arrival-time forecasts was developed based on
the assimilation of magnetohydrodynamic simulations
and the interplanetary scintillation observations by Iwaiet al. (2021).
It is also crucial to investigate the details of the severe
space weather phenomena that occurred in the past fromthe literature and records for considering countermeasures against future space weather disasters. Hayakawa
et al. (2020) reported the record of south American
aurora during the Carrington storm. Oliveira et al. (2020)
investigated a possible case of sporadic aurora observed
at Rio de Janeiro. Kataoka (2020) statistically analyzed
extreme geomagnetic activities.
As mentioned already, solar–terrestrial environment
prediction is necessary to protect the future society.
However, for its development, the cooperation between
various related research fields and their applications isessential. This special issue summarizes the latest efforts
for it. We hope that further study will progress throughthe synergy between scientific research and the operational forecast of space weather.

Saito et al. (2021) estimated the economic impact of
atmospheric radiation storm associated with solar energetic particle (SEP) events on aircraft operations by using
the Warning System for AVIation Exposure to Solar energetic particle (WASAVIES). Oka et al. (2021) analyzed
an unusual short-duration SEP event and found that thehigher-energy (> 30 MeV) protons were detected aboutfour hours after the shock arrival of ICME. The impact ofenergetic particle precipitation on atmospheric chemistry was investigated by Tsuda et al. (2021) and they foundthat the Na loss around the topside of Na layer would be
induced by the energetic particle precipitation.
Many papers on the ionospheric dynamics and its prediction are published by this special issue. Nishioka et al.
(2021) statistically analyzed the extreme states of ionospheric total electron content (TEC) in Japan. Tao et al.
(2020b) also analyzed the statistics of short-wave fadeout
for extreme space weather event estimation. Otsuka et al.
(2021) studied the solar activity dependence of mediumscale traveling ionospheric disturbances (MSTID) using
GPS receivers in Japan. Hosokawa et al. (2020) monitored
the anomalous propagation of aeronautical VHF radio
waves due to sporadic E layer in Japan.
The Ground-to-topside model of Atmosphere andIonosphere for Aeronomy (GAIA) is a powerful tool tosimulate and predict the dynamics of ionosphere andatmosphere. Shinagawa et al. (2021) developed thenumerical prediction of sporadic E layer occurrence
using the GAIA. Ghosh et al. (2020) investigated theday-to-day variation of pre-reversal enhancement in theequatorial ionosphere based on GAIA model simulations.
Sivakandan et al. (2021) compared the seasonal and longitudinal variation of daytime MSTID activity using GPS
observation and GAIA simulations. Tao et al. (2020a)
reported the numerical forecast of the upper atmosphereand ionosphere using GAIA, in particular for ionosphericstorms and sudden stratospheric warming.
The solar cycle dynamics and solar eruptions are themajor cause of space weather variation in the long termand short term, respectively, and their prediction is
one of the most important subjects in this special issue.
The variability of solar differential rotation and meridional flow were analyzed by Imada et al. (2020) using themagnetic element feature tracking technique. Seki et al.
(2021) studied the relationship between three-dimensional velocity of filament eruptions and CME based on
the Doppler observations. A new infrared observation
for solar polarimetry was developed by Hanaoka et al.
(2020).
Nishizuka et al. (2021) reported the operational solar
flare prediction model using Deep Flare Net. Watanabe
et al. (2021) reported the model-based reproduction
and validation of the total spectra of a solar flare andAcknowledgements
This work was supported by JSPS KAKENHI Grant 20H05604.
Authors’ contributions
KK, MI, TB, YM, SY, HL, TO, and KI served as guest editors for this special issue. All
authors read and approved the final manuscript.
Competing interests
The authors declare that they have no competing interests.
Author details
1
Institute for Space-Earth Environmental Research (ISEE), Nagoya University,
Nagoya 464-8601, Japan. 2 National Institute of Information and Communications Technology (NICT), Koganei, Tokyo 184-8795, Japan. 3 Space Weather
Technology Research and Education Center, University of Colorado at Boulder,
Boulder, CO 80309, USA. 4 Institute for Liberal Arts and Sciences, Kyoto University, Kyoto 606-8501, Japan. 5 Earth and Planetary Science Division, Kyushu
University, Fukuoka 819-0395, Japan. 6 Space Weather Prediction Center,
NOAA, Boulder, CO 80305, USA. 7 Astronomical Observatory, Kyoto University,
Kyoto 606-8502, Japan.
Received: 5 October 2021 Accepted: 5 October 2021

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3

Solar-Terrestrial Environment Prediction: Toward the Synergy of Science and Forecasting Operation of Space Weather and Space Climate

FRONTIER LETTER

Open Access

PSTEP: project for solar–terrestrial environment prediction
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, Yûki 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 and Akimasa Yoshikawa
Earth, Planets and Space 2021, 73:159 DOI: 10.1186/s40623-021-01486-1
Received: 17 December 2020, Accepted: 19 July 2021, Published: 5 August 2021

Abstract
Although solar activity may significantly impact the global environment and socioeconomic systems, the mechanisms for solar eruptions and thesubsequent processes have not yet been fully understood. Thus, modern society supported by advanced information systems is at risk fromsevere space weather disturbances. Project for solar–terrestrial environment prediction (PSTEP) was launched to improve this situation throughsynergy between basic science research and operational forecast. The PSTEP is a nationwide research collaboration in Japan and was conductedfrom 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 andTechnology 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 madea significant progress in space weather research and operational forecasts, publishingover 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.

Keywords: Solar physics, Solar–terrestrial environment, Space weather, Earthenvironmental system

Graphical abstract*Corresponding author: Kanya Kusano, kusano@nagoya-u.jp

FULL PAPER

Open Access

Extreme geomagnetic activities: a statistical study
Ryuho Kataoka
Earth, Planets and Space 2020, 72:124 DOI: 10.1186/s40623-020-01261-8
Received: 10 July 2020, Accepted: 25 August 2020, Published: 3 September 2020

Abstract
Statistical distributions are investigated for magnetic storms, suddencommencements (SCs), and substorms to identify the possible amplitude of
the one in 100-year and 1000-year events from a limited data set of less than
100 years. The lists of magnetic storms and SCs are provided from Kakioka
Magnetic Observatory, while the lists of substorms are obtained fromSuperMAG. It is found that majorities of events essentially follow the
log-normal distribution, as expected from the random output from acomplex system. However, it is uncertain that large-amplitude events follow
the same log-normal distributions, and rather follow the power-law
distributions. Based on the statistical distributions, the probable amplitudesof the 100-year (1000-year) events can be estimated for magnetic storms,
SCs, and substorms as approximately 750 nT (1100 nT), 230 nT (450 nT), and5000 nT (6200 nT), respectively. The possible origin to cause the statistical
distributions is also discussed, consulting the other space weather
phenomena such as solar flares, coronal mass ejections, and solar energetic
particles.

Keywords: Magnetic storms, Sudden commencements, Substorms, Solarflares, Coronal mass ejections, Solar energetic particles, Lognormal distributions, Power-law distributions

Graphical abstract

Corresponding author: Ryuho Kataoka, kataoka.ryuho@nipr.ac.jp
4Earth, Planets and Space

FULL PAPER

Open Access

Statistical analysis of short-wave fadeout for extreme space
weather event estimation
Chihiro Tao*, Michi Nishioka, Susumu Saito, Daikou Shiota, Kyoko Watanabe, Naoto Nishizuka,
Takuya Tsugawa and Mamoru Ishii
Earth, Planets and Space 2020, 72:173 DOI: 10.1186/s40623-020-01278-z
Received: 22 May 2020, Accepted: 21 September 2020, Published: 13 November 2020

Abstract
Solar flares trigger an increase in plasma density in the ionosphere including the D region, and cause the absorption of radio waves, especially inhigh-frequency (HF) ranges, called short-wave fadeout (SWF). To evaluate the SWF duration and absorption statistically, we analyze long-term(36 years) ionosonde data observed by the National Institute of Information and Communications Technology (NICT). The minimum reflection
frequency, fmin, is used to detect SWFs from 15-min-resolution ionosonde observations at Kokubunji, Tokyo, from 1981 to 2016. Since fmin varies
with local time (LT) and season, we refer to dfmin, which is defined as fmin subtracted by its 27-day running median at the same LT. We find thatthe occurrence of SWFs detected by three criteria, (i) dfmin ≥ 2.5 MHz, (ii) dfmin ≥ 3.5 MHz, and (iii) blackout, during daytime associated with any
flare(s) greater than the C1 class is maximized at local noon and decreases with increasing
solar zenith angle. We confirm that the dfmin and duration of SWFs increase with the solar
flare class. We estimate the absorption intensity from observations, which is comparable toan empirical relationship obtained from sudden cosmic noise absorption. A generalized
empirical relationship for absorption from long-distance circuits shows quantitatively
different dependences on solar flare flux, solar zenith angle, and frequency caused bydifferent signal passes compared with that obtained from cosmic noise absorption. From
our analysis and the empirical relationships, we estimate the duration of extreme eventswith occurrence probabilities of once per 10, 100, and 1000 years to be 1.8–3.6, 4.0–6.8, and7.4–11.9 h, respectively. The longest duration of SWFs of about 12 h is comparable to thesolar flare duration derived from an empirical relationship between the solar flare durationand the solar active area for the largest solar active region observed so far.

Keywords: Short-wave fadeout (SWF), Dellinger effect, Ionosphere, Solar flare,
Ionosonde, HF radio, Space weather

Graphical abstract*Corresponding author: Chihiro Tao, chihiro.tao@nict.go.jp

FULL PAPER

Open AccessNumerical forecast of the upper atmosphere and ionosphereusing GAIA
Chihiro Tao*, Hidekatsu Jin, Yasunobu Miyoshi, Hiroyuki Shinagawa, Hitoshi Fujiwara,
Michi Nishioka and Mamoru Ishii
Earth, Planets and Space 2020, 72:178 DOI: 10.1186/s40623-020-01307-x
Received: 16 June 2020, Accepted: 4 November 2020, Published: 24 November 2020

Abstract
Upper atmospheric conditions are crucial for the safe operation of spacecraft orbiting near Earth and for communication andpositioning systems using radio signals. To understand and predict the upper atmospheric conditions, which include complex
variations affected by both low altitude and upper surrounding environments, we have developed a quasi-real-time and forecast
simulations using a physical global model, the Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy (GAIA).
The GAIA simulation system provides a global distribution of ionospheric total electron content (TEC) with backgroundatmospheric and electric distributions including a few-days prediction. The prediction accuracy for the detection of significant
ionospheric storms decreases with increasing leadtime, i.e., the duration of the model simulation which
is not constrained by realistic input parameters.
Similar characteristic variations associated withsudden stratospheric warmings (SSWs) are
reproduced with the full or limited input of
meteorological data at least the prior 3 days. This is a
first step toward the usage of GAIA for space
weather forecasting.

Keywords: GAIA, Ionosphere, Upper atmosphere,
Space weather, Real-time simulation

Graphical abstract*Corresponding author: Chihiro Tao, chihiro.tao@nict.go.jp
5Solar-Terrestrial Environment Prediction: Toward the Synergy of Science and Forecasting Operation of Space Weather and Space Climate

FULL PAPER

Open AccessSolar cycle-related variation in solar differential rotationand meridional flow in solar cycle 24
Shinsuke Imada*, Kengo Matoba, Masashi Fujiyama and Haruhisa Iijima
Earth, Planets and Space 2020, 72:182 DOI: 10.1186/s40623-020-01314-y
Received: 12 May 2020, Accepted: 10 November 2020, Published: 26 November 2020

Abstract
a 150 Rising
Sunspot number

100

50

0

100

Latitude [deg]

60N
30N

0

0
-100

30S
60S

-200

Prograde Velocity [m/s]

b 90N

90S

c 90N
10

60N

5

30N

0

0
30S

-5

60S
90S

-10

Prograde Velocity [m/s]

Keywords: Solar surface flow, Solar cycle

Declining

MaximumMonthlyMonthly smoothed

Latitude [deg]We studied temporal variation of the differential rotation and poleward meridional circulation
during solar cycle 24 using the magnetic element feature tracking technique. We used
line-of-sight magnetograms obtained using the helioseismic and magnetic imager aboard
the Solar Dynamics Observatory from May 01, 2010 to March 26, 2020 (for almost the entire
period of solar cycle 24, Carrington rotation from 2096 to 2229) and tracked the magnetic
element features every 1 h. We also estimated the differential rotation and poleward
meridional flow velocity profiles. The observed profiles are consistent with those of previous
studies on different cycles. Typical properties resulting from torsional oscillations can also be
observed from solar cycle 24. The amplitude of the variation was approximately ±10 m s−1.
Interestingly, we found that the average meridional flow observed in solar cycle 24 is fasterthan that observed in solar cycle 23. In particular, during the declining phase of the cycle, themeridional flow of the middle latitude is accelerated from 10 to 17 m s−1, which is almost halfof the meridional flow itself. The faster meridional flow in solar cycle 24 might be the result of
the weakest cycle during the last 100 years.

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Year

Graphical abstract*Corresponding author: Shinsuke Imada, imada@nagoya-u.jp

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Open Access

30
20
10
0
-10
-20
-30
-40
-50
-60
-70
-80

100

Height (km)Earth, Planets and Space 2021, 73:7 DOI: 10.1186/s40623-020-01335-7
Received: 6 July 2020, Accepted: 6 December 2020, Published: 4 January 2021 95

Abstract

90
85

CNA-deviation (dB)

Height (km)We have performed a statistical data analysis on relationship between simultaneous Na density data and cosmic noise
80
absorption (CNA) data, which is an indicator for energetic particle precipitation, obtained
at15Syowa,
912
18 Antarctic
21
24 in 2000–2002.
27
30
33It isMLT (hr)found that the Na densities around the topside of Na layers (above
105
30~95km height) tended to be smaller when the CNA was larger. The
20
100
10
amounts of Na density responses, i.e., Na density decrease or Na loss,
095-10
were increasing with magnetic local time (MLT) from dusk hours to dawn
-20
hours, and those of CNA responses, i.e., CNA increase, were also
-30
90
-40
increasing with MLT. Thus, there were clear negative correlations between
-50
85
-60
the Na density and CNA variations. These results indicate that the Na loss
-70
80
-80
around the topside of Na layer would be induced by the energetic
9
12
15
18
21
24
27
30
33
MLT (hr)particle precipitation, and its effect would be more severe in dawn hours.

Keywords: Na layer, CNA, Energetic particle precipitation,
Geomagnetic activity, Polar region, Syowa

0.5
0.4
0.3
0.2
0.1
0.0
9

12

15

18

21
MLT (hr)24

Graphical abstract*Corresponding author: T. T. Tsuda, takuo.tsuda@uec.ac.jp
6

27

30

33

Na-deviation (%)

T. T. Tsuda*, Y. -M. Tanaka, R. Tozu, K. Takizawa, M. K. Ejiri, T. Nishiyama, T. D. Kawahara
105
and T. Nakamura

Na-deviation (%)

Relationship between Na layer and CNA variations observed
at Syowa, Antarctic

Earth, Planets and Space

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Open Access

Penetration of the electric fields of the geomagnetic suddencommencement over the globe as observed with the HF
Doppler sounders and magnetometers
Takashi Kikuchi*, Jaroslav Chum, Ichiro Tomizawa, Kumiko K. Hashimoto, Keisuke Hosokawa,
Yusuke Ebihara, Kornyanat Hozumi and Pornchai Supnithi
Earth, Planets and Space 2021, 73:10 DOI: 10.1186/s40623-020-01350-8
Received: 28 July 2020, Accepted: 26 December 2020, Published: 6 January 2021

Abstract
Using the HF Doppler sounders at middle and low latitudes (Prague, Czech Republic; Tucuman, Argentina; Zhongli, Republic of China, andSugadaira, Japan), we observed the electric fields of the geomagnetic sudden commencement (SC) propagating near-instantaneously (within
10 s) over the globe. We found that the electric fields of the preliminary impulse (PI) and main impulse (MI) of the SC are in opposite direction toeach other and that the PI and MI electric fields are directed from the dusk to dawn and dawn to dusk, respectively, manifesting the nature of thecurl-free potential electric field. We further found that the onset and peak of the PI
electric field are simultaneous on the day and nightsides (0545, 1250, 1345 MLT)
within the resolution of 10 s. With the magnetometer data, we confirmed thenear-instantaneous development of the ionospheric currents from high latitudes tothe equator and estimated the location of the field-aligned currents that supply theionospheric currents. The global simultaneity of the electric and magnetic fields does
not require the contribution of the magnetohydrodynamic waves in themagnetosphere nor in the F-region ionosphere. The global simultaneity and day–night asymmetry of the electric fields are explained with the ionospheric electric
potentials transmitted at the speed of light by the TM0 mode waves in the Earthionosphere waveguide.

Keywords: HF Doppler sounder, Penetration electric field, Geomagnetic suddencommencement, Preliminary impulse, Global simultaneous onset, TM0
mode wave in the earth-ionosphere waveguide, Polar-equatorial
ionospheric currents

Graphical abstract*Corresponding author: Takashi Kikuchi, kikuchi@isee.nagoya-u.ac.jp

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Open AccessSolar activity dependence of medium-scale travelingionospheric disturbances using GPS receivers in Japan
Yuichi Otsuka*, Atsuki Shinbori, Takuya Tsugawa and Michi Nishioka
Earth, Planets and Space 2021, 73:22 DOI: 10.1186/s40623-020-01353-5
Received: 9 September 2020, Accepted: 31 December 2020, Published: 20 January 2021

Abstract
In order to reveal solar activity dependence of the medium-scale traveling ionospheric disturbances (MSTIDs) at midlatitudes, total electron
content (TEC) data obtained from a Global Positioning System (GPS) receiver network in Japan during 22 years from 1998 to 2019 were analyzed.
We have calculated the detrended TEC by subtracting the 1-h running average from the original TEC data for each satellite and receiver pair, andmade two-dimensional TEC maps of the detrended TEC with a spatial resolution of 0.15° × 0.15° in longitude and latitude. We have investigated
MSTID activity, defined as δI/Ī, where δI and Ī are standard deviation of the detrended TEC and the average vertical TEC within the area of 133.0°–
137.0° E and 33.0°–37.0° N for 1 h, respectively. From each 2-h time series of the detrended TEC data within the same area as the MSTID activity,
auto-correlation functions (ACFs) of the detrended TEC were calculated to estimate the horizontal propagation velocity and direction of the
MSTIDs. Statistical results of the MSTID activity and propagation direction of MSTIDs were consistent with previous studies and support the ideathat daytime MSTIDs could be caused by atmospheric gravity waves, and that nighttime MSTIDs
were caused by electro-dynamical forces, such as the Perkins instability. From the current long-term
observations, we have found that the nighttime MSTID activity and occurrence rate increased withadecreasing solar activity. For the daytime MSTID, the occurrence rate increased with decreasing
solar activity, whereas the MSTID activity did not show distinct solar activity dependence. These
results suggest that the secondary gravity waves generated by dissipation of the primary gravity
waves propagating from below increase under low solar activity conditions. The mean horizontal
phase velocity of the MSTIDs during nighttime did not show a distinct solar activity dependence,
whereas that during daytime showed an anticorrelation with solar activity. The horizontal phasevelocity of the daytime MSTIDs was widely distributed from 40 to 180 m/s under high solar activity
conditions, whereas it ranged between 80 and 200 m/s, with a maximum occurrence at 130 m/s
under low solar activity conditions, suggesting that gravity waves with low phase velocity could be
dissipated by high viscosity in the thermosphere under low solar activity conditions.

Keywords: Ionosphere, Traveling ionospheric disturbance, TID, MSTID, GPS, Total electron
content, TEC, Gravity wave, Perkins instabilityb*Corresponding author: Yuichi Otsuka, otsuka@isee.nagoya-u.ac.jp
7Graphical abstractcdSolar-Terrestrial Environment Prediction: Toward the Synergy of Science and Forecasting Operation of Space Weather and Space Climate

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Development of space environment customized risk estimation
for satellites (SECURES)
Tsutomu Nagatsuma*, Aoi Nakamizo, Yasubumi Kubota, Masao Nakamura, Kiyokazu Koga,
Yoshizumi Miyoshi and Haruhisa Matsumoto
Earth, Planets and Space 2021, 73:26 DOI: 10.1186/s40623-021-01355-x
Received: 22 August 2020, Accepted: 4 January 2021, Published: 25 January 2021

Abstract
Plasma variations in the geospace environment driven by solar wind–magnetosphere interactions are one of the major causes of satellite
anomaly. To mitigate the effect of satellite anomaly, the risk of space weather disturbances predicted by space weather forecasting needs
to be known in advance. However, the risk of satellite anomaly owing to space weather disturbances is not the same for all satellites,
because the risk depends not only on the space environment itself but also on
the design and materials of individual satellites. From the viewpoint of satellite
operators, it is difficult to apply a general alert level of the space environment
to the risk of individual satellites. To provide tailored space weather
information, we have developed SECURES (Space Environment Customized
Risk Estimation for Satellites) by combining models of the space environment
and those of spacecraft charging. In SECURES, we focus on the risk ofspacecraft charging (surface/internal) for geosynchronous satellites. For therisk estimation of surface charging, we have combined the global
magnetosphere magnetohydrodynamics (MHD) model with the satellite
surface charging models. For the risk estimation of internal charging, we havecombined the radiation belt models with the satellite internal charging
models. We have developed prototype products for both types of charging/electrostatic discharge (ESD). The development of SECURES and ourachievements are introduced in this paper.

Keywords: Space weather forecasting, Geospace, Satellite anomaly, Satellite
charging, Customized risk estimation

Graphical abstract*Corresponding author: Tsutomu Nagatsuma, tnagatsu@nict.go.jp

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Open AccessNumerical prediction of sporadic E layer occurrence using
GAIA
Hiroyuki Shinagawa*, Chihiro Tao, Hidekatsu Jin, Yasunobu Miyoshi and Hitoshi Fujiwara
Earth, Planets and Space 2021, 73:28 DOI: 10.1186/s40623-020-01330-y
Received: 19 July 2020, Accepted: 3 December 2020, Published: 27 January 2021

Abstract
A sporadic E layer has significant influence on radio communications and broadcasting, and predicting the occurrence of sporadic E layers is oneof the most important issues in space weather forecast. While sporadic E layer occurrence and the magnitude of the critical sporadic E frequency(foEs) have clear seasonal variations, significant day-to-day variations as well as regional and temporal variations also occur. Because of the highly
complex behavior of sporadic E layers, the prediction of sporadic E layer occurrence has been one of the most difficult issues in space weather
forecast. To explore the possibility of numerically predicting sporadic E layer occurrence, we employed the whole atmosphere–ionosphere
coupled model GAIA, examining parameters related to the formation of sporadic E layer such as vertical ions velocities and vertical ion
convergences at different altitudes between 90 and 150 km. Those parameters in GAIA were compared with the observed foEs data obtained byionosonde observations in Japan. Although the agreement is not very good in the present version of GAIA, the results suggest a possibility that
sporadic E layer occurrence can be numerically predicted using the parameters derived from GAIA. We have recently developed a real-time GAIA
simulation system that can predict atmosphere–ionosphere conditions for a few days ahead. We present an experimental prediction scheme anda preliminary result for predicting sporadic E layer occurrence.

Keywords: Sporadic E layer, Wind shear, Occurrence, Prediction,
GAIA, Model, Vertical ion convergence

Graphical abstract*Corresponding author: Hiroyuki Shinagawa, sinagawa@nict.go.jp
8Earth, Planets and Space

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Open AccessComparison of seasonal and longitudinal variation of daytime
MSTID activity using GPS observation and GAIA simulations
Mani Sivakandan*, Yuichi Otsuka, Priyanka Ghosh, Hiroyuki Shinagawa, Atsuki Shinbori
and Yasunobu Miyoshi
Earth, Planets and Space 2021, 73:35 DOI: 10.1186/s40623-021-01369-5
Received: 7 September 2020, Accepted: 23 January 2021, Published: 4 February 2021

Abstract
The total electron content (TEC) data derived from the GAIA (Ground-to-topside model of Atmosphere Ionosphere for Aeronomy) is used to
study the seasonal and longitudinal variation of occurrence of medium-scale traveling ionospheric disturbances (MSTIDs) during daytime(09:00–15:00 LT) for the year 2011 at eight locations in northern and southern hemispheres, and the results are compared with ground-based
Global Positioning System (GPS)-TEC. To derive TEC variations caused by MSTIDs from the GAIA (GPS) data, we obtained detrended TEC bysubtracting 2-h (1-h) running average from the TEC, and calculated standard deviation of the detrended TEC in 2 h (1 h). MSTID activity wasdefined as a ratio of the standard deviation to the averaged TEC. Both GAIA simulation and GPS observations data show that daytime MSTID
activities in the northern and southern hemisphere (NH and SH) are higher in winter than in other seasons. From the GAIA simulation, theamplitude of the meridional wind variations, which could be representative of gravity waves (GWs), shows two peaks in winter and summer. The
winter peak in the amplitude of the meridional wind variations coincides with the winter peak of the daytime MSTIDs, indicating that the high
GW activity is responsible for the high MSTID activity. On the other hand, the MSTID
activity does not increase in summer. This is because the GWs in the thermosphere
propagate poleward in summer, and equatorward in winter, and the equatorwardpropagating GWs cause large plasma density perturbations compared to thepoleward-propagating GWs. Longitudinal variation of daytime MSTID activity inwinter is seen in both hemispheres. The MSTID activity during winter in the NH is
higher over Japan than USA, and the MSTID activity during winter in the SH is thehighest in South America. In a nutshell, GAIA can successfully reproduce the seasonal
and longitudinal variation of the daytime MSTIDs. This study confirms that GWs
cause the daytime MSTIDs in GAIA and amplitude and propagation direction of theGWs control the noted seasonal variation. GW activities in the middle and lower
atmosphere cause the longitudinal variation.

Keywords: Daytime MSTIDs, GAIA model, GPS, Gravity waves, Meridional wind, TEC

Fig. 1*Corresponding author: Mani Sivakandan, skandanm89@gmail.com; mani.sivakandan@isee.nagoya‑u.ac.jp

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Statistical analysis of ionospheric total electron content(TEC): long-term estimation of extreme TEC in Japan
Michi Nishioka*, Susumu Saito, Chihiro Tao, Daikou Shiota, Takuya Tsugawa and Mamoru Ishii
Earth, Planets and Space 2021, 73:52 DOI: 10.1186/s40623-021-01374-8
Received: 12 July 2020, Accepted: 2 February 2021, Published: 15 February 2021

Abstract
Ionospheric total electron content (TEC) is one of the key parameters for users of radio-based systems, such as the Global Navigation
Satellite System, high-frequency communication systems, and space-based remote sensing systems, since total ionospheric delay is
proportional to TEC through the propagation path. It is important to know extreme TEC values in readiness for hazardous ionosphericconditions. The purpose of this study is to estimate extreme TEC values with occurrences of once per year, 10 years, and hundred years inJapan. In order to estimate the extreme values of TEC, a cumulative distribution function of daily TEC is derived using 22 years of TEC datafrom 1997 to 2018. The extreme values corresponding to once per year and 10 years
are 90 and 110 TECU, respectively, in Tokyo, Japan. On the other hand, the 22-year data
set is not sufficient to estimate the once-per-100-year value. Thus, we use the 62-year
data set of manually scaled ionosonde data for the critical frequency of the F-layer(foF2) at Kokubunji in Tokyo. First, we study the relationship between TEC and foF2 for
22 years and investigate the slab thickness. Then the result is applied to the statistical
distribution of foF2 data for 62 years. In this study, two methods are applied to estimate
the extreme TEC value. In the first method, the distribution of slab thickness is
artificially inflated to estimate extreme TEC values. In the second method, extreme slab
thicknesses are applied to estimate extreme TEC values. The result shows that theonce-per-100-year TEC is about 150–190 TECU at Tokyo. The value is also estimated to
be 180–230 TECU in Kagoshima and 120–150 TECU in Hokkaido, in the southern andnorthern parts of Japan, respectively.
Keywords: Total electron content (TEC), Extreme TEC, Long-term ionosonde
observation, Manually scaled foF2, Slab thickness*Corresponding author: Michi Nishioka, nishioka@nict.go.jp
9Graphical abstract

Solar-Terrestrial Environment Prediction: Toward the Synergy of Science and Forecasting Operation of Space Weather and Space Climate

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Estimate of economic impact of atmospheric radiation storm
associated with solar energetic particle events on aircraft
operations
Susumu Saito*, Navinda Kithmal Wickramasinghe, Tatsuhiko Sato and Daikou Shiota
Earth, Planets and Space 2021, 73:57 DOI: 10.1186/s40623-021-01377-5
Received: 6 August 2020, Accepted: 8 February 2021, Published: 23 February 2021

Abstract
A solar energetic particle (SEP) event generates a shower of secondary generated particles in the Earth’s atmosphere down to lower altitudes tocause an atmospheric radiation storm (ARS). The high-energy secondary particles cause additional radiation dose at altitudes where aircraft flies.
The space weather information provided by the International Civil Aviation Organization (ICAO) designated space weather centers includes
advisories on the solar radiation storm. The Warning System for AVIation Exposure to Solar energetic particle (WASAVIES), we can estimate theeffective dose rate (EDR) along the flight path of the aircraft. However, it has not been well established how the operators of aircraft should reactwith the space weather advisories on the solar radiation storm. By using a flight trajectory generation algorithm and the global EDR distribution,
the economic impacts of ARS associated with SEP events on aircraft operation, namely the flight path length, flight time, and fuel consumption,
are estimated. The conditions of the peak of the ARS event on 20 January 2005 are used. The economic impacts for a flight route from New York,US to Tokyo, Japan, are estimated with constraints in flight routes to avoid the hazard of radiation and compared with those of the reference casewithout the ARS effects. The fuel consumption is shown to increase by 39–69 tons (33–58%) for a twin-engine, wide-body jet passenger aircraft,when a constraint is imposed on the flight altitude only. When the constraints are set on the aircraft altitude and the latitude, the flight time andthe fuel consumption are both increased by 2.2–2.8 h (17–20%) and 32–48
tons (27–41%), respectively. If the ARS event duration is limited for 3 h, theincrease in the fuel consumption is about 7.6–14 tons (6.4–12%). Thiseconomic impact may be reduced, if the space weather nowcast and forecast
for the ARS and an optimal flight trajectory generation algorithm are used
together. Setting more flexible constraints on the flight route and generating
optimal flight trajectories with minimal economic impacts by fully utilizing the
global EDR distribution is the next step.

Keywords: Solar energetic particle event, Radiation, Impact on airplane
operation

Graphical abstract*Corresponding author: Susumu Saito, susaito@mpat.go.jp

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Relationship between three-dimensional velocity offilament eruptions and CME association
Daikichi Seki*, Kenichi Otsuji, Takako T. Ishii, Ayumi Asai and Kiyoshi Ichimoto
Earth, Planets and Space 2021, 73:58 DOI: 10.1186/s40623-021-01378-4
Received: 2 September 2020, Accepted: 10 February 2021, Published: 26 February 2021

Abstract
It is widely recognised that filament disappearances or eruptions are frequently associated with Coronal Mass Ejections (CMEs).
Since CMEs are a major source of disturbances of the space environment surrounding the Earth, it is important to investigate
these associations in detail for the better prediction of CME occurrence. However, the proportion of filament disappearances
associated with CMEs is under debate. The estimates range from ~10 to ~90% and could be affected by the manners to select theevents. In this study, we aim to reveal what parameters control the association between filament eruptions and CMEs. We
analysed the relationships between CME associations and the physical parameters of filaments including their length, maximum
ascending velocity, and direction of eruptions using 28 events of filament eruptions observed in Hα. We found that the productof the maximum radial velocity and the filament length is well correlated with the CME occurrence. If the product is larger than
8.0 × 106 km2 s−1, the filament will become a CME with aprobability of 93%, and if the product is smaller than this value,
it will not become a CME with a probability of 100%. We
suggest a kinetic-energy threshold above which filament
eruptions are associated with CMEs. Our findings also suggest
the importance of measuring the velocity vector of filament
eruption in three-dimensional space for the better prediction of
CME occurrence.

Keywords: Filaments, Filament eruptions, Coronal Mass
Ejections, Hα observation, 3D velocity

Graphical abstract*Corresponding author: Daikichi Seki, seki.daikichi.87s@kyoto-u.jp
10Earth, Planets and Space

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Open Access

Operational solar flare prediction model using Deep FlareNet
Naoto Nishizuka*, Yûki Kubo, Komei Sugiura, Mitsue Den and Mamoru Ishii
Earth, Planets and Space 2021, 73:64 DOI: 10.1186/s40623-021-01381-9
Received: 7 August 2020, Accepted: 17 February 2021, Published: 5 March 2021

Abstract
We developed an operational solar flare prediction model using deep neural networks, named Deep Flare Net (DeFN). DeFN can issue
probabilistic forecasts of solar flares in two categories, such as ≥ M-class and < M-class events or ≥  C-class and < C-class events, occurringin the next 24 h after observations and the maximum class of flares occurring in the next 24 h. DeFN is set to run every 6 h and has been
operated since January 2019. The input database of solar observation images taken by the Solar Dynamic Observatory (SDO) is
downloaded from the data archive operated by the Joint Science Operations Center (JSOC) of Stanford University. Active regions areautomatically detected from magnetograms, and 79 features are extracted from each region nearly in real time using multiwavelength
observation data. Flare labels are attached to the feature database, and then, the database is standardized and input into DeFN for
prediction. DeFN was pretrained using the datasets obtained from 2010 to 2015. The model
was evaluated with the skill score of the true skill statistics (TSS) and achieved predictions
with TSS = 0.80 for ≥  M-class flares and TSS = 0.63 for ≥  C-class flares. For comparison, we
evaluated the operationally forecast results from January 2019 to June 2020. We found that
operational DeFN forecasts achieved TSS = 0.70 (0.84) for ≥  C-class flares with the probability
threshold of 50 (40)%, although there were very few M-class flares during this period and weshould continue monitoring the results for a longer time. Here, we adopted a chronologicalsplit to divide the database into two for training and testing. The chronological split appears
suitable for evaluating operational models. Furthermore, we proposed the use of time-series
cross-validation. The procedure achieved TSS = 0.70 for ≥  M-class flares and 0.59 for ≥  C-classflares using the datasets obtained from 2010 to 2017. Finally, we discuss the standard
evaluation methods for operational forecasting models, such as the preparation ofobservation, training, and testing datasets, and the selection of verification metrics.

Keywords: Solar flares, Space weather forecasting, Prediction, Operational model, Deepneural networks, Verification

Graphical abstract*Corresponding author: Naoto Nishizuka, nishizuka.naoto@nict.go.jp

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Open Access

Validation of computed extreme ultraviolet emission
spectra during solar flares
Shohei Nishimoto*, Kyoko Watanabe, Toshiki Kawai, Shinsuke Imada and Tomoko Kawate
Earth, Planets and Space 2021, 73:79 DOI: 10.1186/s40623-021-01402-7
Received: 5 August 2020, Accepted: 18 March 2021, Published: 25 March 2021

Abstract
X-rays and extreme ultraviolet (EUV) emissions from solar flares rapidly change thephysical composition of the Earth’s thermosphere and ionosphere, thereby causing space
weather phenomena such as communication failures. Numerous empirical and physicalmodels have been developed to estimate the effects of flare emissions on the Earth’s
upper atmosphere. We verified the reproduction of the flare emission spectra using a
one-dimensional hydrodynamic calculation and the CHIANTI atomic database. To validate
the proposed model, we used the observed EUV spectra obtained by the Extreme
ultraviolet variability experiment (EVE) on board the Solar Dynamics Observatory (SDO).
We examined the “EUV flare time-integrated irradiance” and “EUV flare line rise time” of the
EUV emissions for 21 events by comparing the calculation results of the proposed modeland observed EUV spectral data. The proposed model successfully reproduced the EUV
flare time-integrated irradiance of the Fe VIII 131 Å, Fe XVIII 94 Å, and Fe XX133 Å, as well as
the 55–355 Å and 55–135 Å bands. For the EUV flare line rise time, there was an acceptablecorrelation between the proposed model estimations and observations for all Fe flareemission lines. These results demonstrate that the proposed model can reproduce the
EUV flare emission spectra from the emitting plasma with a relatively high formation
temperature. This indicates that the physics-based model is effective for the accurate
reproduction of the EUV spectral irradiance.
Keywords: Solar flare, X-ray emission, EUV emission, Space weather*Corresponding author: Shohei Nishimoto, ed19004@nda.ac.jp
11Graphical abstract

Solar-Terrestrial Environment Prediction: Toward the Synergy of Science and Forecasting Operation of Space Weather and Space Climate

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Spatial scale of geomagnetic Pc5/Pi3 pulsations as a factor of
their efficiency in generation of geomagnetically induced
currents
Nadezda V Yagova*, Vyacheslav A Pilipenko, Yaroslav A Sakharov and Vasily N Selivanov
Earth, Planets and Space 2021, 73:88 DOI: 10.1186/s40623-021-01407-2
Received: 30 June 2020, Accepted: 25 March 2021, Published: 14 April 2021

Abstract
Geomagnetically induced currents (GICs) in a quasi-meridional power transmission line on the Kola Peninsula are analyzed
during the intervals of Pc5/Pi3 (frequency range from 1.5 to 5 mHz) pulsations recorded at the IMAGE magnetometer network.
We have analyzed GIC in a transformer at the terminal station Vykhodnoy (68° N, 33° E) during the entire year of 2015, near the
maximum of the 24th Solar cycle. To quantify the efficiency of GIC generation by geomagnetic pulsations, a ratio between power
spectral densities of GIC and magnetic field variations is introduced. Upon examination of the geomagnetic pulsation efficiency
in GIC generation, the emphasis is given to its dependence on frequency and spatial scale. To estimate pulsation spatial scales inlatitudinal and longitudinal directions, the triangle of stations KEV-SOD-KIL has been used. Large-scale pulsations (with a highspectral coherence, low phase difference, and similar amplitudes at latitudinally separated stations) are found to be more
effective in GIC generation than small-scale pulsations. The GIC
response also depends on the pulsation scale across theelectric power line.

Keywords: Geomagnetically induced currents, Pc5/Pi3
geomagnetic pulsations

Graphical abstract*Corresponding author: Nadezda V Yagova, nyagova@ifz.ru

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Open Access

Model-based reproduction and validation of the total spectraof a solar flare and their impact on the global environment
at the X9.3 event of September 6, 2017
Kyoko Watanabe*, Hidekatsu Jin, Shohei Nishimoto, Shinsuke Imada, Toshiki Kawai,
Tomoko Kawate, Yuichi Otsuka, Atsuki Shinbori, Takuya Tsugawa and Michi Nishioka
Earth, Planets and Space 2021, 73:96 DOI: 10.1186/s40623-021-01376-6
Received: 2 August 2020, Accepted: 8 February 2021, Published: 20 April 2021

Abstract
We attempted to reproduce the total electron content (TEC) variation in the Earth's atmosphere from thetemporal variation of the solar flare spectrum of the X9.3 flare on September 6, 2017. The flare spectrum
from the Flare Irradiance Spectral Model (FISM), and the flare spectrum from the 1D hydrodynamic model,
which considers the physics of plasma in the flare loop, are used in the GAIA model, which is a simulation
model of the Earth's whole atmosphere and ionosphere, to calculate the TEC difference. We thencompared these results with the observed TEC. When we used the FISM flare spectrum, the difference in
TEC from the background was in a good agreement with the observation. However, when the flare
spectrum of the 1D-hydrodynamic model was used, the result varied depending on the presence orabsence of the background. This difference depending on the models is considered to represent which
extreme ultraviolet (EUV) radiation is primarily responsible for increasing TEC. From the flare spectrum
obtained from these models and the calculation result of TEC fluctuation using GAIA, it is considered thatthe enhancement in EUV emission by approximately 15–35 nm mainly contributes in increasing TEC rather
than that of X-ray emission, which is thought to be mainly responsible for sudden ionosphericdisturbance. In addition, from the altitude/wavelength distribution of the ionization rate of Earth's
atmosphere by GAIA (Ground-to-topside Atmosphere and Ionosphere model for Aeronomy), it was foundthat EUV radiation of approximately 15–35 nm affects a wide altitude range of 120–300 km, and TEC
enhancement is mainly caused by the ionization of nitrogen molecules.

Keywords: Solar flares, Dellinger effect, Total electron content, Space weather*Corresponding author: Kyoko Watanabe, kwatana@nda.ac.jp
12Graphical abstract

Earth, Planets and Space

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Open AccessSpace weather benchmarks on Japanese society
Mamoru Ishii*, Daikou Shiota, Chihiro Tao, Yusuke Ebihara, Hitoshi Fujiwara, Takako Ishii,
Kiyoshi Ichimoto, Ryuho Kataoka, Kiyokazu Koga, Yuki Kubo, Kanya Kusano, Yoshizumi Miyoshi,
Tsutomu Nagatsuma, Aoi Nakamizo, Masao Nakamura, Michi Nishioka, Susumu Saito,
Tatsuhiko Sato, Takuya Tsugawa and Shigeo Yoden
Earth, Planets and Space 2021, 73:108 DOI: 10.1186/s40623-021-01420-5
Received: 10 September 2020, Accepted: 17 April 2021, Published: 18 May 2021

Abstract
We surveyed the relationship between the scale of space weather events and their occurrence rate in Japan, and we discussed
the social impact of these phenomena during the Project for Solar–Terrestrial Environment Prediction (PSTEP) in 2015–2019. The
information was compiled for domestic users of space weather forecasts for appropriate preparedness against space weather
disasters. This paper gives a comprehensive summary of the survey, focusing on the fields of electricity, satellite operations,communication and broadcasting, satellite positioning usage,
aviation, human space activity, and daily life on the Earth’s surface,
using the cutting-edge knowledge of space weather. Quantitative
estimations of the economic impact of space weather events onelectricity supply and aviation are also given. Some topics requiring
future research, which were identified during the survey are also
described.

Keywords: Space weather, Benchmark, Extreme event, Societal
impact, Economic impact estimation

Graphical abstract*Corresponding author: Mamoru Ishii, mishii@nict.go.jp

EXPRESS LETTER

Open AccessA possible case of sporadic aurora observed at Rio deJaneiroDenny M. Oliveira*, Hisashi Hayakawa, Ankush Bhaskar, Eftyhia Zesta and Geeta Vichare
Earth, Planets and Space 2020, 72:82 DOI: 10.1186/s40623-020-01208-z
Received: 23 April 2020, Accepted: 24 May 2020, Published: 6 June 2020

Abstract
Being footprints of major magnetic storms and hence major solar eruptions, mid- to low-latitude aurorae have been one of thepathways to understand solar–terrestrial environments. However, it has been reported that aurorae are also occasionallyobserved at low latitudes under low or even quiet magnetic conditions. Such phenomena are known as “sporadic aurorae”. We
report on a historical event observed by a scientist of the Brazilian Empire in Rio de Janeiro on 15 February 1875. We analyze thisevent on the basis of its spectroscopic observations, along with its visual structure and coloration, to suggest this event was a
possible case of sporadic aurorae. Given the absence of worldwide aurora observations on that day as a consequence of low
magnetic activity recorded on the days preceding the observation, in
addition to a detailed description, the event observed can most likely beclassified as a sporadic aurora. We discuss the geographic and magnetic
conditions of that event. Thus, we add a possible case of sporadic aurora
in the South American sector.

Keywords: Space weather, Sporadic aurora, Analysis of historical data

Graphical abstract*Corresponding author: Denny M. Oliveira, denny.m.deoliveira@nasa.gov; denny@umbc.edu
13Solar-Terrestrial Environment Prediction: Toward the Synergy of Science and Forecasting Operation of Space Weather and Space Climate

EXPRESS LETTER

Open Access

Day-to-day variation of pre-reversal enhancement in theequatorial ionosphere based on GAIA model simulations
Priyanka Ghosh*, Yuichi Otsuka, Sivakandan Mani and Hiroyuki Shinagawa
Earth, Planets and Space 2020, 72:93 DOI: 10.1186/s40623-020-01228-9
Received: 22 April 2020, Accepted: 30 June 2020, Published: 6 July 2020

Abstract
Using a whole atmosphere–ionosphere coupled model GAIA (ground-to-topside model of atmosphere and ionosphere), we
have investigated which parameters mainly control day-to-day variation of vertical plasma drift at the evening terminator overmagnetic equator, so-called pre-reversal enhancement (PRE). Day-to-day variations of the peak PRE are compared with those ofelectron density, eastward current density and eastward neutral wind in the E- and F-region over Chumphon (10.7° N, 99.4° E;
0.86° N magnetic latitude), Thailand during equinoctial months in 2011–2013. Eastward neutral wind in the F-region shows
positive correlation with peak PRE, indicating that the F-region winds control the peak PRE through the mechanisms of theF-region dynamo (including E- and F-region coupling processes). Daytime eastward electric current at an altitude of 110 km,
corresponding to equatorial electro jet(EEJ), is also positively correlated withthe peak PRE. Correlation between the
EEJ and PRE is the largest at 1700 LT,
approximately 1.5 h prior to the peakPRE.

Keywords: Pre-reversal

enhancement, Eastward
neutral wind, Eastward
current density, Electron
density, GAIA
Graphical abstract*Corresponding author: Priyanka Ghosh, iam.priyankaghosh@gmail.com

EXPRESS LETTER

Open AccessSouth American auroral reports during the Carrington
storm
Hisashi Hayakawa*, José R. Ribeiro, Yusuke Ebihara, Ana P. Correia and Mitsuru Sôma
Earth, Planets and Space 2020, 72:122 DOI: 10.1186/s40623-020-01249-4
Received: 24 May 2020, Accepted: 10 August 2020, Published: 26 August 2020

Abstract
The importance of the investigation of magnetic superstorms is not limited to academic interest, because these superstorms cancause catastrophic impact on the modern civilisation due to our increasing dependency on technological infrastructure. In thiscontext, the Carrington storm in September 1859 is considered as a benchmark of observational history owing to its magnetic
disturbance and equatorial extent of the auroral oval. So far, several recent auroral reports at that time have been published but
those reports are mainly derived from the Northern Hemisphere. In this study, we analyse datable auroral reports from SouthAmerica and its vicinity, assess the auroral extent using philological and astrometricNaapproaches, identify the auroral visibility at − 17.3° magnetic latitude and furtherbpoleward and reconstruct the equatorial boundary of the auroral oval to be 25.1° ± 0.5°
in invariant latitude. Interestingly, brighter and more colourful auroral displays werereported in the South American sector than in the Northern Hemisphere. This north–south asymmetry is presumably associated with variations of their magnetic longitude
and the weaker magnetic field over South America compared to the magneticEW
conjugate point and the increased amount of magnetospheric electron precipitation
E
into the upper atmosphere. These results attest that the magnitude of the Carrington
storm indicates that its extent falls within the range of other superstorms, such as thosethat occurred in May 1921 and February 1872, in terms of the equatorial boundary of
the auroral oval.

Keywords: Low-latitude aurorae, Auroral oval, Geomagnetic storms, Coronal massejections, Historical records, Space weather, Extreme space weather
events, Carrington storm*Corresponding author: Hisashi Hayakawa, hisashi@nagoya-u.jp
14SGraphical abstract

Earth, Planets and Space

EXPRESS LETTER

Open Access

Validation of coronal mass ejection arrival-time forecasts bymagnetohydrodynamic simulations based oninterplanetary scintillation observations
Kazumasa Iwai*, Daikou Shiota, Munetoshi Tokumaru, Ken’ichi Fujiki, Mitsue Den and Yûki Kubo
Earth, Planets and Space 2021, 73:9 DOI: 10.1186/s40623-020-01345-5
Received: 26 May 2020, Accepted: 23 December 2020, Published: 6 January 2021

Abstract

Keywords: Interplanetary scintillation, Coronal mass ejection, Space

Speed (km/s)

Y [radian]Coronal mass ejections (CMEs) cause various disturbances of the space environment; therefore, forecasting their arrival time is very important.
However, forecasting accuracy is hindered by limited CME observations in interplanetary space. This study investigates the accuracy of CME
arrival times at the Earth forecasted by three-dimensional (3D) magnetohydrodynamic (MHD) simulations based on interplanetary scintillation(IPS) observations. In this system, CMEs are approximated as spheromaks with various initial speeds. Ten MHD simulations with different CME
initial speed are tested, and the density distributions derived from each simulation run are compared with IPS data observed by the Institute forSpace-Earth Environmental Research (ISEE), Nagoya University. The CME arrival time of the simulation run that most closely agrees with the IPS
data is selected as the forecasted time. We then validated the accuracy of this forecast using 12 halo CME events. The average absolute arrivaltime error of the IPS-based MHD forecast is approximately 5.0 h, which is one of the most accurate predictions that ever been validated, whereasthat of MHD simulations without IPS data, in which the initial CME speed isderived from white-light coronagraph images, is approximately 6.7 h. This
Simulated speed at the EarthIPS at 327MHz (BG: MHD, Symb: OBS)
800
1.5suggests that the assimilation of IPS data into MHD simulations can improve
1.8
700
the accuracy of CME arrival-time forecasts. The average predicted arrival times
1.0
1.6
are earlier than the actual arrival times. These early predictions may be due to600
0.5
overestimation of the magnetic field included in the spheromak and/or
1.4
0.0
500
underestimation of the drag force from the background solar wind, the latter-0.5
of which could be related to underestimation of CME size or background solar
1.2400
wind density.
-1.0-1.5 2017.09.07 01:01-1.5 -1.0 -0.5 0.0 0.5
X [radian]weather forecasting, Magnetohydrodynamics, Dataassimilation

1.0

1.0

1.5

300
200

15:00 18:00 21:00 00:00 03:00 06:00
Start Time (07-Sep-17 12:30:00)

Graphical abstract*Corresponding author: Kazumasa Iwai, k.iwai@isee.nagoya-u.ac.jp

EXPRESS LETTER

Open Access

Unusual enhancement of ~ 30 MeV proton flux in an ICME
sheath region
Mitsuo Oka*, Takahiro Obara, Nariaki V. Nitta, Seiji Yashiro, Daikou Shiota and Kiyoshi Ichimoto
Earth, Planets and Space 2021, 73:31 DOI: 10.1186/s40623-021-01362-y
Received: 9 August 2020, Accepted: 15 January 2021, Published: 29 January 2021

Abstract
In gradual Solar Energetic Particle (SEP) events, shock waves driven by coronal mass ejections (CMEs) play a major role inaccelerating particles, and the energetic particle flux enhances substantially when the shock front passes by the observer. Suchenhancements are historically referred to as Energetic Storm Particle (ESP) events, but it remains unclear why ESP time profiles
vary significantly from event to event. In some cases, energetic protons are not even clearly associated with shocks. Here, wereport an unusual, short-duration proton event detected on 5 June 2011 in the compressed sheath region bounded by aninterplanetary shock and the leading edge of the interplanetary CME (or ICME) that was driving the shock. While < 10 MeV
protons were detected already at the shock front, the higher-energy (> 30 MeV) protons were detected about four hours after theshock arrival, apparently correlated with a turbulent
magnetic cavity embedded in the ICME
sheath region.
10
Protons [cm-2 s-1 sr-1 MeV-1]

2

Keywords: Particle acceleration, Solarenergetic particles, Turbulence,
Coronal mass ejections,Interplanetary shocks

GOES/EPEAD: 15-40 MeV

20-25 MeV
101 SOHO/ERNE:
Wind/EPACT: 19-28 MeV
STA/HET: 20.8-23.8 MeV

100 STB/HET: 20.8-23.8 MeV
10-1
10-2
10-3
10-4
03-Jun04-Jun05-Jun06-JunStart Time (2011/06/03 00:00)

Graphical abstract*Corresponding author: Mitsuo Oka, moka@berkeley.edu
15

Solar-Terrestrial Environment Prediction: Toward the Synergy of Science and Forecasting Operation of Space Weather and Space Climate

TECHNICAL REPORT

Open Access

A monitoring network for anomalous propagation of
aeronautical VHF radio waves due to sporadic E in Japan
Keisuke Hosokawa*, Jun Sakai, Ichiro Tomizawa, Susumu Saito, Takuya Tsugawa, Michi Nishioka
and Mamoru Ishii
Earth, Planets and Space 2020, 72:88 DOI: 10.1186/s40623-020-01216-z
Received: 23 April 2020, Accepted: 20 June 2020, Published: 1 July 2020

Abstract
We introduce a network observation of anomalous long-distance propagation of aeronautical navigation (NAV) very high-frequency (VHF) radio
waves due to sporadic E layer (Es). The system has been operative since May 2019 at 6 stations in Japan. The receiver consists of a log-periodic
antenna, air-band filter, software-defined radio and small computer which is capable of recording the strength of radio signals in the frequency
band from 98 to 118 MHz with a temporal resolution of 2 s. The receiver covers not only the NAV band including VHF omnidirectional radio range(VOR), instrument landing system localizer (ILS LOC) and ground-based augmentation system VHF data broadcast (GBAS VDB) from 108 to 118
MHz, but also broadcasting channels from 98 to 108 MHz. Soon after the start of the full operation of the network observation, a strong Es event
was detected by an ionosonde in Tokyo during the daytime on July 4, 2019, in which foEs (critical frequency of Es) was sometimes higher than 15
MHz. The VHF radio wave monitoring system detected multiple signatures of Es anomalous propagation (EsAP) at all the stations extending from
Okinawa to Hokkaido. At some stations, the EsAP signatures continued for a few hours with some brief intervals of disappearance. The observed
correspondence between the enhancement of foEs and the occurrence of anomalous propagation confirmed that an extreme electron density
enhancement within Es caused the anomalous long-distance propagation of VHF NAV signals. The data from this network observation can bebrowsed at http://gwave.cei.uec.ac.jp/cgi-bin/vor/vhf.cgi in near real-time basis. This near real-time monitoring capability allows people in the
aeronautical operation community such as air navigation service providers, pilots, and airline engineers to check the propagation environment of
VHF NAV signals online, which contributes to a mitigation ofSporadic E
Mid-Point (Reflection Point)
ionospheric space weather impacts on the aeronautical navigation
100 km Altitude
systems. Not only that the current method for detecting Es in a wide
area can be used to visualize the spatial distribution of Es in twoNormal Propagation
dimensional fashion through a combination of other observation
techniques such as ionosondes and total electron content (TEC)
600 - 2000 km
measurements using Global Navigation Satellite System (GNSS) signals.
< 200 km

Keywords: Ionosphere, Sporadic E, Radio propagation, Aeronautical

GroundVOR Station: Tx

Receiving Station: Rx

Fig. 1navigation system, Software radio*Corresponding author: Keisuke Hosokawa, keisuke.hosokawa@uec.ac.jp

TECHNICAL REPORT

Open Access

A HAWAII-2RG infrared camera operated under fast
readout mode for solar polarimetry
Yoichiro Hanaoka*, Yukio Katsukawa, Satoshi Morita, Yukiko Kamata and Noriyoshi Ishizuka
Earth, Planets and Space 2020, 72:181 DOI: 10.1186/s40623-020-01318-8
Received: 4 July 2020, Accepted: 19 November 2020, Published: 26 November 2020

Abstract
Polarimetry is a crucial method to investigate solar magnetic fields. From the viewpoint of space weather, the magnetic field in
solar filaments, which occasionally erupt and develop into interplanetary flux ropes, is of particular interest. To measure themagnetic field in filaments, high-performance polarimetry in the near-infrared wavelengths employing a high-speed, largeformat detector is required; however, so far, this has been difficult to be realized. Thus, the development of a new infrared camera
for advanced solar polarimetry has been started, employing a HAWAII-2RG (H2RG) array by Teledyne, which has 2048 ×2048
pixels, focusing on the wavelengths in the range of 1.0−1.6 μm. We solved the problem of the difficult operation of the H2RGs
under “fast readout mode” synchronizing with high-speed polarization modulation by introducing a “MACIE” (Markury ASIC
Control and Interface Electronics) interface
card and new assembly codes provided bya Stokes I
b Stokes V/I c Map
He I 1083.0
Markury Scientific. This enables polarization
measurements with high frame-rates, such as
29–117 frames per seconds, using a H2RG. We
conducted experimental observations of the
Sun and confirmed the high polarimetricperformance of the camera.

0.02

0.00

200

d SDO/HMI Magne

150

100

50

Keywords: Solar observation, Polarimetry,-0.02

Magnetic field, Space weather,
Near-infrared, H2RG

0

Si I 1082.7

Graphical abstract*Corresponding author: Yoichiro Hanaoka, yoichiro.hanaoka@nao.ac.jp
16

800

850

900

Earth, Planets and SpaceTECHNICAL REPORT

Open AccessMeasurement of geomagnetically induced current (GIC)
around Tokyo, Japan
Shinichi Watari*, Satoko Nakamura and Yusuke Ebihara
Earth, Planets and Space 2021, 73:102 DOI: 10.1186/s40623-021-01422-3
Received: 11 August 2020, Accepted: 23 April 2021, Published: 7 May 2021

Abstract
We need a typical method of directly measuring geomagnetically induced current (GIC) to compare data for estimating a
potential risk of power grids caused by GIC. Here, we overview GIC measurement systems that have appeared in publishedpapers, note necessary requirements, report on our equipment, and show several examples of our measurements in substations
around Tokyo, Japan. Although they are located at middle latitudes, GICs associated with various geomagnetic disturbances areobserved, such as storm sudden commencements (SSCs) or
sudden impulses (SIs) caused by interplanetary shocks,
Data Logger Box
geomagnetic storms including a storm caused by abrupt
GPS Antennasouthward turning of strong interplanetary magnetic field (IMF)
associated with a magnetic cloud, bay disturbances caused by
Data Logger
Ba eryhigh-latitude aurora activities, and geomagnetic variation caused
Sensor Box
by a solar flare called the solar flare effect (SFE). All these results
Clamp-typesuggest that GIC at middle latitudes is sensitive to the
Switching Hub
Sensor Unit
Current Sensor
magnetospheric current (the magnetopause current, the ring
Remote Tap
current, and the field-aligned current) and also the ionosphericcurrent.

Keywords: Geomagnetically induced current (GIC), Equipment,

Storm sudden commencement (SSC), Sudden
impulse (SI), Geomagnetic storm, Bay disturbance,
Solar flare effect (SFE), Magnetic cloud, Space weather*Corresponding author: Shinichi Watari, watari@nict.go.jp

17

UPS

Mobile Router
Antenna

Block diagram of the GIC measurement system

Graphical abstract

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Continued from back coverSouth American auroral reports during the Carrington storm...................................................................................Hisashi Hayakawa, José R. Ribeiro, Yusuke Ebihara, Ana P. Correia and Mitsuru Sôma   14Validation of coronal mass ejection arrival-time forecasts by magnetohydrodynamic simulations based oninterplanetary scintillation observations...............................................................Kazumasa Iwai, Daikou Shiota, Munetoshi Tokumaru, Ken’ichi Fujiki, Mitsue Den and Yûki Kubo   15Unusual enhancement of ~ 30 MeV proton flux in an ICME sheath region.................................................................Mitsuo Oka, Takahiro Obara, Nariaki V. Nitta, Seiji Yashiro, Daikou Shiota and Kiyoshi Ichimoto   15A monitoring network for anomalous propagation of aeronautical VHF radio waves due to sporadic E in Japan...............................Keisuke Hosokawa, Jun Sakai, Ichiro Tomizawa, Susumu Saito, Takuya Tsugawa, Michi Nishioka and Mamoru Ishii   16A HAWAII-2RG infrared camera operated under fast readout mode for solar polarimetry.......................................................................Yoichiro Hanaoka, Yukio Katsukawa, Satoshi Morita, Yukiko Kamata and Noriyoshi Ishizuka   16Measurement of geomagnetically induced current (GIC) around Tokyo, Japan.......................................................................................................................................Shinichi Watari, Satoko Nakamura and Yusuke Ebihara   17Cover image: Kusano, K. et al., Earth, Planets and Space 2021, 73:159 DOI: 10.1186/s40623-021-01486-1

Contents
Special issue “Solar–terrestrial environment prediction: toward the synergy of science and forecasting operation of
space weather and space climate” ....................................................Kanya Kusano, Mamoru Ishii, Tomas Berger, Yoshizumi Miyoshi,
Shigeo Yoden, Huixin Liu, Terry Onsager and Kiyoshi Ichimoto

1

PSTEP: project for solar–terrestrial environment prediction.................................................... 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, Yûki 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 and Akimasa Yoshikawa
Extreme geomagnetic activities: a statistical study ..............................................................................................................Ryuho Kataoka

Statistical analysis of short-wave fadeout for extreme space weather event estimation................................................................................................. Chihiro Tao, Michi Nishioka, Susumu Saito, Daikou Shiota, Kyoko Watanabe,
Naoto Nishizuka, Takuya Tsugawa and Mamoru Ishii

Numerical forecast of the upper atmosphere and ionosphere using GAIA.................................................................................................................Chihiro Tao, Hidekatsu Jin, Yasunobu Miyoshi, Hiroyuki Shinagawa,
Hitoshi Fujiwara, Michi Nishioka and Mamoru Ishii

Solar cycle-related variation in solar differential rotation and meridional flow in solar cycle 24.......................................................................................................... Shinsuke Imada, Kengo Matoba, Masashi Fujiyama and Haruhisa Iijima
Relationship between Na layer and CNA variations observed at Syowa, Antarctic.................................................... T. T. Tsuda, Y. -M. Tanaka, R. Tozu, K. Takizawa, M. K. Ejiri, T. Nishiyama, T. D. Kawahara and T. Nakamura
Penetration of the electric fields of the geomagnetic sudden commencement over the globe as observed with the HF
Doppler sounders and magnetometers ..........................Takashi Kikuchi, Jaroslav Chum, Ichiro Tomizawa, Kumiko K. Hashimoto,Keisuke Hosokawa, Yusuke Ebihara, Kornyanat Hozumi and Pornchai Supnithi

Solar activity dependence of medium-scale traveling ionospheric disturbances using GPS receivers in Japan................................................................................................................ Yuichi Otsuka, Atsuki Shinbori, Takuya Tsugawa and Michi Nishioka
Development of space environment customized risk estimation for satellites (SECURES).................................................................................................... Tsutomu Nagatsuma, Aoi Nakamizo, Yasubumi Kubota, Masao Nakamura,Kiyokazu Koga, Yoshizumi Miyoshi and Haruhisa Matsumoto

Numerical prediction of sporadic E layer occurrence using GAIA............................................................................Hiroyuki Shinagawa, Chihiro Tao, Hidekatsu Jin, Yasunobu Miyoshi and Hitoshi Fujiwara
Comparison of seasonal and longitudinal variation of daytime MSTID activity using GPS observation and GAIA
simulations ...................................................................................Mani Sivakandan, Yuichi Otsuka, Priyanka Ghosh, Hiroyuki Shinagawa,Atsuki Shinbori and Yasunobu Miyoshi

Statistical analysis of ionospheric total electron content (TEC): long-term estimation of extreme TEC in Japan.................................................................. Michi Nishioka, Susumu Saito, Chihiro Tao, Daikou Shiota, Takuya Tsugawa and Mamoru Ishii
Estimate of economic impact of atmospheric radiation storm associated with solar energetic particle events on aircraft
operations .............................................................Susumu Saito, Navinda Kithmal Wickramasinghe, Tatsuhiko Sato and Daikou Shiota
Relationship between three-dimensional velocity of filament eruptions and CME association................................................................................................Daikichi Seki, Kenichi Otsuji, Takako T. Ishii, Ayumi Asai and Kiyoshi Ichimoto
Operational solar flare prediction model using Deep Flare Net....................................................................................................Naoto Nishizuka, Yûki Kubo, Komei Sugiura, Mitsue Den and Mamoru Ishii
Validation of computed extreme ultraviolet emission spectra during solar flares.......................................................................... Shohei Nishimoto, Kyoko Watanabe, Toshiki Kawai, Shinsuke Imada and Tomoko Kawate
Spatial scale of geomagnetic Pc5/Pi3 pulsations as a factor of their efficiency in generation of geomagnetically induced
currents ............................................................Nadezda V Yagova, Vyacheslav A Pilipenko, Yaroslav A Sakharov and Vasily N Selivanov
Model-based reproduction and validation of the total spectra of a solar flare and their impact on the global
environment at the X9.3 event of September 6, 2017...................................................... Kyoko Watanabe, Hidekatsu Jin, Shohei Nishimoto, Shinsuke Imada, Toshiki Kawai, Tomoko Kawate,
Yuichi Otsuka, Atsuki Shinbori, Takuya Tsugawa and Michi Nishioka

4
4

5

5
6
6

7
7

8
8

9
9
10
10
11
11
12

12

Space weather benchmarks on Japanese society............... Mamoru Ishii, Daikou Shiota, Chihiro Tao, Yusuke Ebihara, Hitoshi Fujiwara, Takako Ishii, Kiyoshi Ichimoto, Ryuho Kataoka,
Kiyokazu Koga, Yuki Kubo, Kanya Kusano, Yoshizumi Miyoshi, Tsutomu Nagatsuma, Aoi Nakamizo, Masao Nakamura,Michi Nishioka, Susumu Saito, Tatsuhiko Sato, Takuya Tsugawa and Shigeo Yoden

13

A possible case of sporadic aurora observed at Rio de Janeiro............................................................................. Denny M. Oliveira, Hisashi Hayakawa, Ankush Bhaskar, Eftyhia Zesta and Geeta Vichare 13
Day-to-day variation of pre-reversal enhancement in the equatorial ionosphere based on GAIA model simulations.................................................................................................... Priyanka Ghosh, Yuichi Otsuka, Sivakandan Mani and Hiroyuki Shinagawa 14

Continued on inside back cover