Extremely Severe Space Weather and Geomagnetically Induced Currents
in Regions with Locally Heterogeneous Ground Resistivity

Editorial Board (May 2016)
Editor-in-Chief
Yasuo Ogawa, Tokyo Institute of Technology, Japan

Editorial Board
Yosuke Aoki, University of Tokyo, Japan
Nanan Balan, University of Sheffield, United
Kingdom
Stephen Bannister, GNS Science, New Zealand
Benjamin Fong Chao, Academia Sinica, Taiwan
Shanaka de Silva, Oregon State University, U.S.A.
Koji Fukuma, Doshisha University, Japan
Lin-Ni Hau, National Central University, Taiwan
Hauke Hussmann, German Aerospace Center,
Germany
Hiroo Kanamori, California Institute ofTechnology, U.S.A.
Attila Komjathy, National Aeronautics and Space
Administration, U.S.A.
Alexey Kuvshinov, Swiss Federal Institute ofTechnology Zurich, Switzerland
Takuto Maeda, University of Tokyo, Japan
Koji Matsumoto, National Astronomical
Observatory, Japan
Mitsuhiro Nakagawa, Hokkaido University, Japan

Junichi Nakajima, Tokyo Institute of Technology,
Japan
Yasuhiro Nariyuki, University of Toyama, Japan
Nozomu Nishitani, Nagoya University, Japan
Azusa Nishizawa, Japan Coast Guard, Japan
Keiji Ohtsuki, Kobe University, Japan
Taku Ozawa, National Research Institute for Earth
Science and Disaster Prevention, Japan
Takeshi Sakanoi, Tohoku University, Japan
Martha K. Savage, Victoria University of
Wellington, New Zealand
Benoit Taisne, Nanyang Technological University,
Singapore
Hiroshi Takenaka, Okayama University, Japan
Hiroaki Toh, Kyoto University, Japan
Yih-Min Wu, National Taiwan University, Taiwan
Zhongliang Wu, China Earthquake Administration,
China
Akimasa Yoshikawa, Kyushu University, Japan

Journal Scope
Earth, Planets and Space (EPS) is the official journal of the 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.
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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.
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Earth, Planets and Space
Fujita et al. Earth, Planets and Space (2016) 68:51
DOI 10.1186/s40623-016-0428-yOpen Access

PREFACE

Extremely severe space weather
and geomagnetically induced currents
in regions with locally heterogeneous groundresistivity
Shigeru Fujita1*, Ryuho Kataoka2, Ikuko Fujii1, Antti Pulkkinen3 and Shinichi Watari4
variations are composed of magnetic variations caused
by magnetospheric and ionospheric disturbances andby currents induced in the ground. The magnetosphericdisturbances in turn are driven by coronal mass ejections
and other solar disturbances transmitted through interplanetary space. Furthermore, the effective applicationof a GIC study (e.g., disaster mitigation) requires assessment of how large and how often severe GICs occur in a
specific area. Thus, the frequency of severe space weather
events also needs to be characterized. At the same time,
the heterogeneous distribution of the ground resistivity is important to assess local enhancements of the GIE.
Scientists try to understand extreme space weather andpredict a realistic GIC, and this special issue of 19 papers
publishes recent research achievements about extremely
severe space weather and the GIC in the realistic heterogeneous ground resistivity structure.
The influence of the heterogeneous resistivity structure is important for the reproduction of realistic GIEs
and GICs from magnetic storm data. Ten papers in thiscollection address this topic. The influence of the heterogeneous resistivity structure to GIEs is investigatedusing the geoelectric data obtained continuously at Japanese magnetic observatories (Fujii et al. 2015). Love andSwidinsky (2015) also discuss the geoelectric data fromthe Kakioka Magnetic Observatory based on a twolayer lithosphere model. Goto (2015) calculates the GIEin the coastal zone with a strong spatial gradient in theresistivity and in the seafloor region with a homogeneous resistivity structure. Alekseev et al. (2015) construct
the heterogeneous resistivity structure in the Earth,which is important for the evaluation of the GIEs. Pulkkinen et al. (2015b) demonstrate that the GIEs also canbe locally enhanced when the source structure is highly
heterogeneous. Next, realistic reproduction of GIEs andLarge geomagnetically induced currents (GICs) triggeredby extreme space weather events are now regarded as oneof the serious natural threats to the modern electrified
society. The risk is described in detail in High-Impact,
Low-Frequency Event Risk, A Jointly-Commissioned
Summary Report of the North American Electric Reliability Corporation and the US Department of Energy’s
November 2009 Workshop, June 2010. For example, theMarch 13–14, 1989 storm caused a large-scale blackout affecting about 6 million people in Quebec, Canada,
and resulting in substantial economic losses in Canada
and the USA (Bolduc 2002). Therefore, European andNorth American nations have invested in GIC researchsuch as the “Solar Shield project” in the USA (Pulkkinen et al. 2009, 2015a). In 2015, the Japanese government (Ministry of Economy, Trade and Industry, METI)
acknowledged the importance of GIC research in Japan.
After reviewing the serious damages caused by the 2011
Tohoku-Oki earthquake, METI recognized the potential
risk to the electric power grid posed by extreme space
weather. During extreme events, GICs can be concerning
even in mid- and low-latitude countries and have become
a global issue.
From the scientific and technological aspect, GIC studies are interdisciplinary and include research in Earth’s
electromagnetism, magnetospheric and ionosphericphysics, interplanetary physics, and solar physics. The
GIC is determined by the geomagnetically induced electric field (GIE) and the DC characteristics of the electric
power grid. GIEs are controlled by magnetic variations in
the ground and the Earth’s resistivity. Ground magnetic*Correspondence: sfujita@mc‑jma.go.jp
1
Meteorological College, Kashiwa, Japan
Full list of author information is available at the end of the article© 2016 Fujita et al. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License(http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium,provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license,
and indicate if changes were made.

1

Extremely Severe Space Weather and Geomagnetically Induced Currents in Regions with Locally Heterogeneous Ground Resistivity
Fujita et al. Earth, Planets and Space (2016) 68:51

Page 2 of 3

the characteristics of extreme solar flares and associatedinterplanetary transport of the energetic solar particles.
Maehara et al. (2012, 2015) discuss the possibility of asuper solar flare (Maehara et al. 2012) based on the solar
type of stars observed by the Kepler space telescope.
Kubo et al. (2015) present a model reproducing the transport of energetic solar particles that can pose a hazard tosatellites.
Between 2011 and 2015, we held annual symposia about
extreme space weather and a special symposium celebrating the centennial anniversary of geomagnetic observation at the Kakioka Magnetic Observatory in 2013. The
intensive discussions at these symposia between participants from different fields stimulated deep insight into
physical processes of these events, and a special issue wasplanned. In addition, a new Japanese research project
about space weather (PSTEP—Project for Solar-Terrestrial Environment Prediction) will be conducted between
2015 and 2019 (http://www.pstep.jp/?lang=en). This project will support research on solar physics, interplanetary
physics, magnetospheric physics, and GICs as well as
research on the sun–climate relationship. The topics covered in this special issue provided an important springboard for the PSTEP project.

GICs from the magnetic storm data is reported by several papers. Püthe et al. (2014) calculate the GIE on the
ground with heterogeneous resistivity structure driven
by a real magnetic storm and accurately predict the GIE
using their model. Beggan (2015) performs numericalstudies of the GIE driven by the auroral electrojet. Beggan
also uses a thin sheet model and estimates the GIC using
electric power grid data from the UK. Watari (2015) predicts the GIC by using the transfer function between theobserved GICs and the magnetic variations in Hokkaido,
Japan. This technique was developed by Pulkkinen et al.
(2007). Torta et al. (2014) study the GIC in the electric
power grid in Spain by using a plane-wave model withuniform ground resistivity. Last, Xu et al. (2015) evaluate
the induction effects driven by the magnetospheric ring
current.
In space science and solar physics, detailed dynamics of the severe space weather events are still poorly
understood. In addition, because GICs have societal
implications, it is important to know the frequency ofoccurrence of severe space weather events. Therefore,
we need to investigate the properties of large solar eruptions that can trigger extreme space weather events andcan also transport of high-energy solar particles to the
Earth. Nine papers discuss these topics. First, four papers
discuss the physical processes associated with extreme
magnetospheric disturbances such as the Carrington
storm of September 1859 (the largest magnetic storm
on record) (Keika et al. 2015), the March 13–14, 1989
magnetic storm (Nagatsuma et al. 2015), and the suddencommencement (SC) in 1940 (the largest SC since 1868)(Araki 2014). Keika et al. (2015) discuss the rapid recovery of the Carrington storm that may have been causedby the flow-out of the ring current associated with fastmagnetospheric plasma convection. Nagatsuma et al.
(2015) describe magnetospheric processes such as a long
duration of the geosynchronous magnetopause crossing during the March 1989 storm, which lacks interplanetary data. They estimate interplanetary magnetic
field (IMF) Bz of about −50 nT and solar wind speed ofabout 960 km/s. Similar to the large SC study by Araki(2014), Kubota et al. (2015) study characteristics of large
SCs modeled with a global magnetosphere–ionosphere
coupled MHD simulation. Next, three papers deal withstatistical studies of the magnetospheric disturbances.
Nakamura et al. (2015) study the auroral electrojets, andMinamoto et al. (2015) address the magnetic storms andSCs observed by the Kakioka Magnetic Observatory.
The frequencies of occurrence of severe space weather
are useful not only to the scientists but also to society.
Hayakawa et al. (2015) present the historical records ofauroras observed during the Chinese dynasty (Song) intenth–thirteenth centuries. The last two papers report

Author details
1
Meteorological College, Kashiwa, Japan. 2 National Institute of Polar Research,
Tachikawa, Japan. 3 NASA Goddard Space Flight Center, Greenbelt, MD, USA.
4
National Institute of Information and Communications Technology, Koganei,
Japan.
Received: 17 March 2016 Accepted: 18 March 2016

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Extremely Severe Space Weather and Geomagnetically Induced Currents in Regions with Locally Heterogeneous Ground Resistivity

FRONTIER LETTER Open Access

Statistical properties of superflares on solar-type stars basedon 1-min cadence data
Hiroyuki Maehara*, Takuya Shibayama, Yuta Notsu, Shota Notsu, Satoshi Honda, Daisaku Nogami
and Kazunari Shibata
Earth, Planets and Space 2015, 67:59 DOI: 10.1186/s40623-015-0217-z
Received: 30 September 2014, Accepted: 23 March 2015, Published: 29 April 2015

Abstract
We searched for superflares on solar-type stars using Kepler data with 1-min sampling in order to detect superflares with ashort duration. We found 187 superflares on 23 solar-type stars whose bolometric energy ranges from the order of 1032 to1036 erg. Some superflares show multiple peaks with the peak separation of the order of 100 to 1,000 s which is comparable tothe periods of quasi-periodic pulsations in solar and stellar flares. Using these new data combined with the results from thedata with 30-min sampling, we found that the occurrence frequency (dN/dE) of superflares as a function of flare energy (E)shows the power-law distribution (dN/dE ∝ E −α ) with α ~ −1.5 for 1033 < E < 1036 erg which is consistent with the previous
results. The average occurrence rate of superflares with the energy of 1033 erg which is equivalent to X100 solar flares is about
once in 500 to 600 years. The upper limit of energy released by superflares is basically comparable to a fraction of themagnetic energy stored near starspots which is estimated from the photometry.
We also found that the duration of superflares (τ) increases with theflare energy (E) as τ ∝ E 0.39 ± 0.03. This can be explained if we assume(a)(b)
the time scale of flares is determined by the Alfvén time.

Keywords: Superflares; Solar flares; Stellar flares; Solar-type stars;
Extreme space weather events

Figure 1*Corresponding author: Hiroyuki Maehara, h.maehara@oao.nao.ac.jp

FRONTIER LETTER Open AccessRegional-scale high-latitude extreme geoelectric fields pertaining
to geomagnetically induced currents
Antti Pulkkinen*, Emanuel Bernabeu, Jan Eichner, Ari Viljanen and Chigomezyo Ngwira
Earth, Planets and Space 2015, 67:93 DOI: 10.1186/s40623-015-0255-6
Received: 6 November 2014, Accepted: 21 May 2015, Published: 19 June 2015

Abstract
Motivated by the needs of the high-voltage power transmission industry, we use data from the high-latitude IMAGE
magnetometer array to study characteristics of extreme geoelectric fields at regional scales. We use 10-s resolution data foryears 1993–2013, and the fields are characterized using average horizontal geoelectric field amplitudes taken over stationgroups that span about 500-km distance. We show that geoelectric field structures associated with localized extremes atsingle stations can be greatly different from structures associated with regionally
Geoelectric field distribution at 07:32:20 UT. Max. |E|: 4.41 V/km.
uniform geoelectric fields, which are well represented by spatial averages over single
75
N
stations. Visual extrapolation and rigorous extreme value analysis of spatially averaged
400 km70
300
N
fields indicate that the expected range for 1-in-100-year extreme events are 3–8 V/km
200
100
and 3.4–7.1 V/km, respectively. The Quebec reference ground model is used in the0calculations.
oGeomanetic latitude [deg]oE

4Keywords: Geomagnetically induced currents; Extreme events; Spatial scales

14

72 o
E

o

65 o 1 V/km
N

60 o
N

Figure 1*Corresponding author: Antti Pulkkinen, antti.a.pulkkinen@nasa.gov
4oGeomagnetic longitude [deg]

E
126

108oE

90 oE

55 oN

Earth, Planets and Space

FULL PAPER

Open Access

Assessing the hazard from geomagnetically induced currents
to the entire high-voltage power network in Spain
Joan Miquel Torta*, Santiago Marsal and Marta Quintana
Earth, Planets and Space 2014, 66:87 DOI: 10.1186/1880-5981-66-87
Received: 28 January 2014, Accepted: 16 July 2014, Published: 4 August 2014

Abstract
After the good results obtained from an assessment of geomagnetically induced currents (GICs) in a relatively small subset of
the Spanish power transmission network, we now present the first attempt to assess vulnerability across the entire Spanish
system. At this stage, we have only included the power grid at the voltage level of 400 kV, which contains 173 substations
along with their corresponding single or multiple transformers and almost 300 transmission lines; this type of analysis could
be extended to include the 220-kV grid, and even the 110-kV lines, if more detailed information becomes available. The
geoelectric field that drives the GICs can be derived with the assumption of plane
wave geomagnetic variations and a homogeneous or layered conductivity structure.
To assess the maximum expected GICs in each transformer as a consequence of
extreme geomagnetic storms, a post-event analysis of data from the Ebre
Geomagnetic Observatory (EBR) during the 2003 Halloween storm was performed,
although other episodes coincident with very abrupt storm onsets, which have
proven to be more hazardous at these mid-latitudes, were analyzed as well. Preferredgeomagnetic/geoelectric field directions in which the maximum GICs occur areautomatically given from the grid model. In addition, EBR digital geomagnetic data
were used to infer statistical occurrence probability values and derive the GIC risk at
100-year or 200-year return period scenarios. Comparisons with GIC measurements
at one of the transformers allowed us to evaluate the model uncertainties.
400 kV network

500

142

100

400

144

161

24

79

97

117

300

89
145

39
74

129

34

109
118

42

136

81

103

135

8

54 149
152

172

100

5

138

71

49 65 119North [km]

139

10

46

82

63

37

0

73

83

137

80

106

147

−100

166

25
163 17

57

93

160

31

105

101
170

26

11

30

154

32

61

53

69
150

85
126

36

21

113

104

45

14
90

120

121

12

165

41

127

40

43

15

68

55

−300

−400

102
87

38

23

158

−200

Keywords: Geomagnetically induced currents; GIC; Space weather; Natural hazards;

20

156

157

66

115
28
98
29
107
19
51

7

91

131

132

84

124

4

169

96
78 76
13
44 153159
9151

48 128

22

27

95

47

123

77

114

60

134

75
108

125
92

171 3

162

168

110

35
116

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86

200

1−linemultiple

143
52
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94 130 112
16
2 164 1
140
6
56
62
133
50 18
141
88
59 67
146

70

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155
148
122

173

−500

−400

Spain

−300

−200

−100

0

100

200

300

400

500

East [km]Figure 1*Corresponding author: Joan Miquel Torta, jmtorta@obsebre.es

FULL PAPER

Open Access

Reproducing electric field observations during magnetic storms bymeans of rigorous 3-D modelling and distortion matrix co-estimation
Christoph Püthe*, Chandrasekharan Manoj and Alexey Kuvshinov
Earth, Planets and Space 2014, 66:162 DOI: 10.1186/s40623-014-0162-2
Received: 19 September 2014, Accepted: 22 November 2014, Published: 23 December 2014

Abstract
Electric fields induced in the conducting Earth by geomagnetic disturbances drive currents in power transmission grids,
telecommunication lines or buried pipelines, which can cause service disruptions. A key step in the prediction of the hazard totechnological systems during magnetic storms is the calculation of the geoelectric field. To address this issue for mid-latitude
regions, we revisit a method that involves 3-D modelling of induction processes in a heterogeneous Earth and theconstruction of a magnetospheric source model described by low-degree spherical harmonics from observatory magnetic
data. The actual electric field, however, is known to be perturbed by galvanic effects, arising fromvery local near-surface heterogeneities or topography, which cannot be included in the model.
Galvanic effects are commonly accounted for with a real-valued time-independent distortion
matrix, which linearly relates measured and modelled electric fields. Using data of six magnetic
storms that occurred between 2000 and 2003, we estimate distortion matrices for observatory
sites onshore and on the ocean bottom. Reliable estimates are obtained, and the modellings arefound to explain up to 90% of the measurements. We further find that 3-D modelling is crucial fora correct separation of galvanic and inductive effects and a precise prediction of the shape ofelectric field time series during magnetic storms. Since the method relies on precomputed
responses of a 3-D Earth to geomagnetic disturbances, which can be recycled for each storm, therequired computational resources are negligible. Our approach is thus suitable for real-time
prediction of geomagnetically induced currents by combining it with reliable forecasts of thesource field.

Keywords: Magnetic storms; Geomagnetically induced currents; Geoelectric field; Static shift;Distortion matrix; 3-D modelling

Figure 1*Corresponding author: Christoph Püthe, christoph.puethe@erdw.ethz.ch
5Extremely Severe Space Weather and Geomagnetically Induced Currents in Regions with Locally Heterogeneous Ground Resistivity

FULL PAPER

Open AccessObserved geomagnetic induction effect on Dst-related magnetic
observations under different disturbance intensities ofthe magnetospheric ring current
Dan Xu*, Huaran Chen and Mengtan Gao
Earth, Planets and Space 2015, 67:15 DOI: 10.1186/s40623-015-0189-z
Received: 26 July 2014, Accepted: 15 January 2015, Published: 30 January 2015

Abstract
Based on the spherical harmonic expansion of geomagnetic disturbance observed on the mid-latitude surface of the Earth, external and internal
field separation is conducted in which the external component is magnetic disturbance caused by the magnetospheric ring current and theinternal component is that raised by the correspondingly induced currents within the Earth. The objectives are to evaluate the influences of theinduced internal field on the surface magnetic observations and to reveal the response performance of internal geomagnetic induction under
different strengths of magnetospheric ring current fluctuations for better understanding of the disturbance storm time (Dst) index variations. The
results show that the ratio of the internal component to surface observation does not remain constant in storm time. During the main phase of
the storm, the ratio variation follows the pattern of logarithmic growth with storm evolution up to the top value at the Dst-minimum; then, theratio slowly decreases in the long recovery phase. Multiple small logarithmic growths aresuperimposed on the traces of internal ratios, corresponding to temporary ring current
intensification during the storm main phase and amplifying the effect of this intensification on
surface magnetic observations. With the intensification of magnetospheric storms from the level of(−200 nT, − 100 nT) to (−300 nT, − 200 nT) and (−500 nT, − 300 nT) classified with the Dst-minimum,
the top value of the ratio averaged for each storm group in the superposed epoch analysis method
increases from the value of 0.295 ± 0.014 to 0.300 ± 0.016 and 0.308 ± 0.015, respectively. It isdemonstrated that the geomagnetic induction exceeds the linear relation with the intensificationof the external field, which is physically reasonable and coincident with the Faraday’s law of
induction. Due to the effects of high induction of the oceans and lateral heterogeneity of electric
conductivity distribution in the upper mantle of the Earth, the geomagnetic induction and its
contribution to surface geomagnetic disturbance vary significantly among observatories. Thisfactor should be considered in the research of magnetospheric current systems.

Keywords: Geomagnetic storms; Geomagnetic induction; Dst index

Figure 1*Corresponding author: Dan Xu, danxu@outlook.com

FULL PAPER

Open AccessSensitivity of geomagnetically induced currents to varying auroralelectrojet and conductivity models
Ciarán D Beggan
Earth, Planets and Space 2015, 67:24 DOI: 10.1186/s40623-014-0168-9
Received: 8 September 2014, Accepted: 6 December 2014, Published: 15 February 2015

Abstract
Geomagnetically induced currents (GIC) are created by the interaction of rapid changes in the magnitude of the magnetic
field with the conductive subsurface of the Earth. The changing magnetic field induces electric currents, which are particularly
strong along boundaries between regions of contrasting conductivity structure such as the land and sea. A technique known
as the ‘thin-sheet approximation’ can be used to determine the electric field at the Earth’s surface, which in turn allows thecalculation of GIC in the earthing connections of high-voltage nodes within a power grid. The thin-sheet approximation uses aspatially varying conductance over the region of interest on a 2D surface, combinedwith a 1D layered model of upper lithosphere conductance. We produce synthetic
models of the auroral electrojet in different locations over the United Kingdom (UK)and investigate the effects of varying the 2D thin-sheet model. We assess different
two-dimensional surface conductance models and vary the underlying 1D
conductivity models to simulate the effects of resistant through to conductive
lithosphere. With an advanced network model of high-voltage electrical distribution
grid, we compute the expected GIC at each node in the system given the input
surface electric fields from the various synthetic electrojets and conductivity models.
We find that the electrojet location is the primary control on the size of GIC, with
conductivity being a second-order effect in general, though it can be locallyimportant.

Keywords: Geomagnetically induced currents; Ground conductivity; Electric field
Corresponding author: Ciarán D Beggan, ciar@bgs.ac.uk
6

Figure 1

Earth, Planets and Space

FULL PAPER

Open AccessObservatory geoelectric fields induced in a two-layer lithosphere
during magnetic storms
Jeffrey J Love* and Andrei Swidinsky
Earth, Planets and Space 2015, 67:58 DOI: 10.1186/s40623-015-0213-3
Received: 23 August 2014, Accepted: 14 March 2015, Published: 28 April 2015

Abstract
We report on the development and validation of an algorithm for estimating geoelectric fields induced in the lithospherebeneath an observatory during a magnetic storm. To accommodate induction in three-dimensional lithospheric electricalconductivity, we analyze a simple nine-parameter model: two horizontal layers, each with uniform electrical conductivity
properties given by independent distortion tensors. With Laplace transformation of the induction equations into the complex
frequency domain, we obtain a transfer function describing induction of observatory geoelectric fields having frequencydependent polarization. Upon inverse transformation back to the time domain, the convolution of the corresponding
impulse-response function with a geomagnetic time series yields an estimated geoelectric time series. We obtain an
optimized set of conductivity parameters using 1-s resolution
geomagnetic and geoelectric field data collected at the Kakioka,
Japan, observatory for five different intense magnetic storms,
including the October 2003 Halloween storm; our estimatedgeoelectric field accounts for 93% of that measured during theHalloween storm. This work demonstrates the need for detailed
modeling of the Earth’s lithospheric conductivity structure and theutility of co-located geomagnetic and geoelectric monitoring.

Keywords: Magnetic storm; Induction hazard; Geomagnetic andgeoelectric fields; Time-series analysis; Operationalalgorithm

Figure 1*Corresponding author: Jeffrey J Love, jlove@usgs.gov

FULL PAPER 

Open Access

The characteristics of geoelectric fields at Kakioka, Kanoya, andMemambetsu inferred from voltage measurements during 2000 to 2011
Ikuko Fujii*, Takashi Ookawa, Shingo Nagamachi and Takeshi Owada
Earth, Planets and Space 2015, 67:62 DOI: 10.1186/s40623-015-0241-z
Received: 7 November 2014, Accepted: 23 April 2015, Published: 8 May 2015

Abstract
Geoelectric voltages have been continuously observed at Kakioka, Kanoya, and Memambetsu for more than 50 years. The
geoelectric fields obtained at the three sites for a recent 11-year period (2000 to 2011) were examined. The fields are mainly
induced by variations in the geomagnetic field at periods of less than 105 s. The instability of the observation system causes along-term trend in the longer period band. This long-term trend can be estimated and removed using the robust Kalman filter
procedure which we modified to accommodate data containing outliers. The magnetotelluric (MT) impedance at the three sites
was estimated using the original geoelectric field and the geomagnetic field at periods of
6 to 104 s, and the period was extended to 107 s at Kakioka and Memambetsu. Although
the geomagnetically induced currents (GIC) at these sites may potentially be estimatedusing the MT impedance and geomagnetic data (if technological network information isavailable), the distortion effect should be corrected in order to obtain the correct regionalgeoelectric field. The eastward component of the geoelectric field at Kakioka shows asevere distortion effect, and the amplification factor was estimated to be approximately
10 from comparison with the C response at Kakioka. Conversely, the distortion effect on
the eastward component of the geoelectric field at Memambetsu is almost none. The
amplification factor for the northward component of the geoelectric field has not been
estimated because of the lack of an independent response for comparison, although the
MT response indicates a potentially large distortion at Memambetsu. Numerical modelingwould be a useful tool to enable an improved estimation of this distortion.

Keywords: Geoelectric field; Kakioka; Memambetsu; Kanoya; Electromagnetic

induction; Conductivity distribution; Geomagnetically induced current*Corresponding author: Ikuko Fujii, ifujii@mc-jma.go.jp
7

Figure 1Extremely Severe Space Weather and Geomagnetically Induced Currents in Regions with Locally Heterogeneous Ground Resistivity

FULL PAPER

Open Access

What caused the rapid recovery of the Carrington storm?
Kunihiro Keika*, Yusuke Ebihara and Ryuho Kataoka
Earth, Planets and Space 2015, 67:65 DOI: 10.1186/s40623-015-0234-y
Received: 4 November 2014, Accepted: 17 April 2015, Published: 8 May 2015

Abstract
The geomagnetic storm during the Carrington event, which occurred on 2 September 1859, displayed extremely rapid
recovery. The geomagnetic field increased by approximately 650 nT/h at Bombay, India, and by >300 nT/h in 1-h averaged
data. Although the rapid recovery is considered due to a sudden increase in the magnetopause current, a sudden decrease of
the ring current, or/and a sudden enhancement of the ionospheric currents, this study focuses on the ring current decay. The
Carrington rapid recovery had a time constant (approximately 1 h) comparable to the storm development (i.e., decrease in thegeomagnetic field), indicating that energy loss from the ring current region is predominantly controlled by E × B convection
transport which is responsible for energy input during the storm main phase. This feature has led us to a hypothesis that theflow-out of dense ring current ions and injections of tenuous plasma sheet ions caused the rapid decay of the ring current andin turn the storm rapid recovery. This study examines whether the Carrington rapid recovery can be explained by the flow-out
effect. We extend the empirical Burton’s model to a model that takes into consideration a sudden change in solar wind density
which is correlated with plasma sheet density. We first apply the extended Burton’smodel to previously observed four intense magnetic storms (Dst minimum< −200 nT) for which solar wind data are available. Using the best fit parameters
found by forward modeling, the extended model estimates the recovery of the
Carrington storm. The estimate indicates that a solar wind structure with a density
bump by approximately 100 cm−3 (and southward interplanetary magnetic field(IMF) of 65 nT and solar wind speed of 1,500 km/s) can cause the rapid recovery
under a continuous southward IMF condition. We conclude that the flow-out effectplays a significant role in producing the rapid recovery of the Carrington storm.

Keywords: Intense magnetic storms; Ring current; Storm rapid recovery; Flow-out
loss; Carrington event; Plasma sheet density change

Figure 1*Corresponding author: Kunihiro Keika, kkeika@stelab.nagoya-u.ac.jp

FULL PAPER

Open Access

Estimation of geomagnetically induced currents based on
the measurement data of a transformer in a Japanese power networkand geoelectric field observations
Shinichi Watari
Earth, Planets and Space 2015, 67:77 DOI: 10.1186/s40623-015-0253-8
Received: 26 October 2014, Accepted: 19 May 2015, Published: 27 May 2015

Abstract
Geomagnetically induced currents (GICs) have the potential to cause electric power blackouts. Hence, it is important to study
the effects of GICs produced by intense geomagnetic storms. The measurements of GICs were conducted at the Memanbetsu
substation, Hokkaido, between December 2005 and March 2008. We obtain the complementary cumulative distributionfunction (CCDF) of the measured GICs and the empirical equation to estimate GICs
using the GIC data and geoelectric field observation data. GICs associated with thepast intense geomagnetic storms, e.g., the March 13–15 storm and the October 29–30,
2003 storm, are estimated.

Keywords: Geomagnetically induced current (GIC); Geomagnetic storm; Geoelectricfields; Space weather

Figure 1

Corresponding author: Shinichi Watari, watari@nict.go.jp
8Earth, Planets and Space

FULL PAPER 

Open Access

Estimating the solar wind conditions during an extreme geomagnetic
storm: a case study of the event that occurred on March 13–14, 1989
Tsutomu Nagatsuma*, Ryuho Kataoka and Manabu Kunitake
Earth, Planets and Space 2015, 67:78 DOI: 10.1186/s40623-015-0249-4
Received: 31 October 2014, Accepted: 15 May 2015, Published: 27 May 2015

Abstract
The solar wind conditions of an extreme geomagnetic storm were examined using
magnetic field observations obtained from geosynchronous satellites and the
disturbance storm-time (Dst) index. During geosynchronous magnetopausecrossings (GMCs), magnetic field variations at the magnetosheath, which is themodulated interplanetary magnetic field (IMF), were observed by geosynchronous
satellite. The dawn to dusk solar wind electric field (VBS) was estimated from the Dst
index by using an empirical formula for Dst prediction; these data were then used toestimate the IMF and solar wind speed. This method was applied in the analysis ofan extreme geomagnetic storm event that occurred on March 13–14, 1989, forwhich no direct solar wind information was available. A long duration of the GMC
was observed after the second storm sudden commencement (SSC) of this event.
The solar flare possibly associated with the second SSC of this storm event was
identified as the March 12 M7.3/2B flare. The IMF Bz was estimated to be about−50 nT with a solar wind speed of about 960 km/s during the 5 h in which the main
phase of the storm rapidly developed, assuming an Alfvén Mach number (MA)during this period of more than 2.

Keywords: Extreme geomagnetic storm; Geosynchronous magnetopause crossing;Geomagnetic indices; Solar wind parameters–

Figure 1*Corresponding author: Tsutomu Nagatsuma, tnagatsu@nict.go.jp

FULL PAPER

Open Access

Records of sunspot and aurora during CE 960–1279
in the Chinese chronicle of the Sòng dynasty
Hisashi Hayakawa*, Harufumi Tamazawa, Akito Davis Kawamura and Hiroaki Isobe
Earth, Planets and Space 2015, 67:82 DOI: 10.1186/s40623-015-0250-y
Received: 30 September 2014, Accepted: 16 May 2015, Published: 29 May 2015

Abstract
Records of sunspot and aurora observations in pre-telescopic historical documents can provide useful information about solar
activity in the past. This is also true for extreme space weather events, as they may have been recorded as large sunspots
observed by the naked eye or as low-latitude auroras. In this paper, we present the results of a comprehensive survey ofrecords of sunspots and auroras in the Sòngshı̌, a Chinese formal chronicle spanning the tenth to the thirteenth century. This
chronicle contains a record of continuous observations with well-formatted reports conducted as a policy of the government.
A brief comparison of the frequency of observations of sunspots and auroras and the observations of radioisotopes as anindicator of the solar activity during corresponding periods is provided. This paper is the first step of our project in which wesurvey and compile the records of sunspots and auroras in historical documents from various locations and languages,
ultimately providing it to the science community as online data.

Keywords: Aurora; Sunspot; Solar activity; Chinesechronicle; Historical resource

Figure 1*Corresponding author: Hisashi Hayakawa, hayakawa@kwasan.kyoto-u.ac.jp
9Extremely Severe Space Weather and Geomagnetically Induced Currents in Regions with Locally Heterogeneous Ground Resistivity

FULL PAPER

Open AccessCompilation of 3D global conductivity model of the Earthfor space weather applications
Dmitry Alekseev*, Alexey Kuvshinov and Nikolay Palshin
Earth, Planets and Space 2015, 67:108 DOI: 10.1186/s40623-015-0272-5
Received: 30 September 2014, Accepted: 13 June 2015, Published: 4 July 2015

Abstract
We have compiled a global three-dimensional (3D) conductivity model of the Earth with an ultimate goal to be used forrealistic simulation of geomagnetically induced currents (GIC), posing a potential threat to man-made electric systems.
Bearing in mind the intrinsic frequency range of the most intense disturbances (magnetospheric substorms) with typicalperiods ranging from a few minutes to a few hours, the compiled 3D model represents the structure in depth range of 0–100
km, including seawater, sediments, earth crust, and partly the lithosphere/asthenosphere. More explicitly, the model consistsof a series of spherical layers, whose vertical and lateral boundaries are established based on available data. To compile amodel, global maps of bathymetry, sediment thickness, and upper and lower crust thicknesses as well as lithosphere thickness
are utilized. All maps are re-interpolated on a common grid of 0.25 × 0.25 degree lateral spacing. Once the geometry ofdifferent structures is specified, each element of the structure is assigned either a certain conductivity value or conductivity
versus depth distribution, according to available laboratory data and conversion laws. A numerical formalism developed forcompilation of the model, allows for its further refinement by incorporation of regional 3D conductivity distributions inferredfrom the real electromagnetic data. So far we included into our model four regional conductivity models, available fromrecent publications, namely, surface conductance model of Russia, and 3D
conductivity models of Fennoscandia, Australia, and northwest of the United States.

Keywords: Global 3-D conductivity model; Geomagnetically induced currents;
Magnetospheric substorms; Geoelectric field

Figure 1*Corresponding author: Dmitry Alekseev, alexeevgeo@gmail.com

LETTER

Open AccessHistorically largest geomagnetic sudden commencement (SC) since
1868
Tohru Araki
Earth, Planets and Space 2014, 66:164 DOI: 10.1186/s40623-014-0164-0
Received: 26 September 2014, Accepted: 27 November 2014, Published: 9 December 2014

Abstract
Being stimulated by the previously reported large amplitude (202 nT at Kakioka) geomagnetic
sudden commencement (SC) on 24 March 1991, we searched larger amplitude SCs in the past.
We tried to collect old magnetograms and used the list of SC observed at Kakioka (27.5° gm.
lat.) for the period 1924 to 2013 and Colaba (10.5°)-Alibag (10.3°) for 1868 to 1967. We foundthat the largest amplitude SC occurred on 24 March (the same day as 1991 SC), 1940. The
H-component amplitude is larger than 273 nT at Kakioka and 310 nT at Alibag. We could also
obtain the copy of the magnetogram of Cape Town (−33.3°) which shows 164 nT amplitude.
The statistical analysis shows that the occurrence rate of SCs is less than 5% for amplitudelarger than 50 nT and less than 1% for amplitude larger than 100 nT at both Kakioka andAlibag. Large amplitude SCs tend to occur during the declining phase of the solar activity.
Finally, we discussed the possible increase of the dynamic pressure associated with theinterplanetary shock causing the largest SC.

Keywords: Geomagnetic sudden commencement (SC); Solar activity; Largest SC;
Interplanetary shock

Figure 1

Corresponding author: Tohru Araki, tohru.araki.24m@st.kyoto-u.ac.jp
10Earth, Planets and SpaceLETTER

Open Access

Global MHD simulation of magnetospheric responseof preliminary impulse to large and sudden enhancementof the solar wind dynamic pressure
Yasubumi Kubota*, Ryuho Kataoka, Mitsue Den, Takashi Tanaka, Tsutomu Nagatsuma and Shigeru Fujita
Earth, Planets and Space 2015, 67:94 DOI: 10.1186/s40623-015-0270-7
Received: 10 July 2014, Accepted: 10 June 2015, Published: 19 June 2015

Abstract
A sudden increase in the dynamic pressure of solar wind generates a prominent and transient change in ground-basedmagnetometer records worldwide, which is called a sudden commencement (SC). The magnetic field variation due to an SC athigh latitudes shows a bipolar change, which consists of a preliminary impulse (PI) and main impulse (MI). The largest
recorded SC had an amplitude of more than 200 nT with a spiky waveform at low latitudes, and the mechanism causing thissuper SC is unknown. Here, we investigate the cause of the super SC using a newly developed magnetosphere-ionosphere
coupling simulation, which enables us to investigate the magnetospheric response to a large increase in the solar winddynamic pressure. To simulate SCs, the dynamic pressure of the solar wind is increased to 2, 5, 10, and 16 larger than that
under the stationary condition, and two different types of dynamic
pressure increase are adopted by changing the solar wind density
only or the solar wind speed only. It was found that the magnetic
field variations of the PI and MI are several times larger and faster fora jump in the speed than for a jump in the density. It is inferred that asolar wind velocity of more than 2500 km/s in the downstream shock,which cannot be directly simulated in this study, would be consistent
with the super SC.

Keywords: Sudden commencement; Extreme solar wind event;
MHD simulation; Magnetosphere

Figure 1*Corresponding author: Yasubumi Kubota, ykubota@nict.go.jp

LETTER

Open Access

Statistical analysis of extreme auroral electrojet indicesMasao Nakamura*, Asato Yoneda, Mitsunobu Oda and Ken Tsubouchi
Earth, Planets and Space 2015, 67:153 DOI: 10.1186/s40623-015-0321-0
Received: 29 December 2014, Accepted: 2 September 2015, Published: 16 September 2015

Abstract
Extreme auroral electrojet activities can damage electrical power grids due to large induced currents in the Earth, degrade
radio communications and navigation systems due to the ionospheric disturbances and cause polar-orbiting satellite
anomalies due to the enhanced auroral electron precipitation. Statistical estimation of extreme auroral electrojet activities is
an important factor in space weather research. For this estimation, we utilize extreme value theory (EVT), which focuses on
the statistical behavior in the tail of a distribution. As a measure of auroral electrojet activities, auroral electrojet indices AL,
AU, and AE, are used, which describe the maximum current strength of the westward and eastward auroral electrojets and thesum of the two oppositely directed in the auroral latitude ionosphere, respectively. We provide statistical evidence for finite
upper limits to AL and AU and estimate the annual expected number and probable intensity of their extreme events. We
detect two different types of extreme AE events; therefore, application of the appropriate EVT analysis to AE is difficult.

Keywords: Auroral electrojet activity; AE AU AL index;
Extreme value theory; Space weather

Figure 1*Corresponding author: Masao Nakamura, nakamura@aero.osakafu-u.ac.jp
11Extremely Severe Space Weather and Geomagnetically Induced Currents in Regions with Locally Heterogeneous Ground Resistivity

LETTER

Open AccessFrequency distributions of magnetic storms and SI+SSC-derived
records at Kakioka, Memambetsu, and Kanoya
Yasuhiro Minamoto*, Shigeru Fujita and Masahiro Hara
Earth, Planets and Space 2015, 67:191 DOI: 10.1186/s40623-015-0362-4
Received: 24 December 2014, Accepted: 24 November 2015, Published: 28 November 2015

Abstract
The Japan Meteorological Agency keeps records of geomagnetic phenomena observed at Kakioka (magnetic latitude, 27.47°),
Memambetsu (magnetic latitude, 35.44°), and Kanoya (magnetic latitude, 22.00°). We used these records to examine thecumulative frequency distribution of magnetic storms, sudden impulses, and storm sudden commencements. The
distributions of magnetic storms resemble the Gutenberg–Richter relation between earthquake frequency and magnitudeused in seismology. The coefficients determined with the maximum likelihood method show that when the H-range of amagnetic storm at Kakioka is doubled, the frequency of the magnetic storm is about one seventh, for example. Intense
magnetic storms occur less frequently than calculated by the functions. This statistical analysis proves that there are no
significant differences between slopes of the frequency distribution functions of the magnetic phenomena at Kakioka,
Memambetsu, and Kanoya.

Keywords: Magnetic storm; Sudden impulses; Storm sudden commencements;(a)Power law

Figure 1*Corresponding author: Yasuhiro Minamoto, minamoto.yasuhiro@nipr.ac.jp

LETTER

Open AccessNumerical studies of geomagnetically induced electric field on
seafloor and near coastal zones incorporated with heterogeneous
conductivity distributions
Tada-nori Goto
Earth, Planets and Space 2015, 67:193 DOI: 10.1186/s40623-015-0356-2
Received: 15 January 2015, Accepted: 10 November 2015, Published: 2 December 2015

Abstract
Abrupt changes of geomagnetic field can make large induced electric field and resultant electric current on the earth, which is called
as geomagnetically induced current (GIC). It can yield damages to pipelines, cables, and other architectures. For understanding thephenomena and future risks of GIC, it is necessary to evaluate how the sub-surface electrical conductivity structure is important for the
GIC because the heterogeneous conductivity structure in the crust and mantle affects the induced electrical current locally. The hazard
prediction based on the homogeneous earth may result in the underestimation. Here, I introduce possible cases of geomagneticallyinduced electric field (GIE) on seafloor and near coastal areas, based on numerical forward simulations on one-, two-, and threedimensional (1-D, 2-D, and 3-D) earth’s structure including the sea layer. On the 1-D case, I show the possible amplitude of GIE on theseafloor, far from the coastal area. The second case study comes from 2-D forward simulation, in which the straightly elongated coastalline is assumed, and various sub-surface and sub-seafloor conductivity structures are imposed. The numerical results suggest that theamplitude of GIE on land becomes more than two times larger than that of the
100
1000 sec
100 sec
homogeneous earth without the sea layer. The width of land zone with larger GIE is about
20 km from the coast. In forward modeling with a simplified 3-D bathymetry, land electric
10
No Seawater
field near the bay area increases with about ten times larger than that of the inland one.
The seafloor GIE near the peninsula area also indicates about four times larger value than1that of the other area at the same water depth. These phenomena can be explained by theWater Depth = 1000 m
boundary charge along the coastal area. I conclude that 3-D earth’s conductivity structure
0.1
Water Depth = 4000 m
including the realistic bathymetry and sub-surface and sub-seafloor structures should be
essential and focused for the hazard assessment of GIC.
0.01
0.0001

Keywords: GIC; Conductivity structure; Seafloor; Coastal effectCorresponding author: Tada-nori Goto, goto.tadanori.8a@kyoto-u.ac.jp
12

0.001

0.01

0.1

Frequency (Hz)Figure 11

10Earth, Planets and SpaceTECHNICAL REPORT

Open AccessInterplanetary particle transport simulation for warning system
for aviation exposure to solar energetic particlesYûki Kubo*, Ryuho Kataoka and Tatsuhiko Sato
Earth, Planets and Space 2015, 67:117 DOI: 10.1186/s40623-015-0260-9
Received: 18 September 2014, Accepted: 2 June 2015, Published: 29 July 2015

Abstract
Background: Solar energetic particles (SEPs) are one of the extreme space weather phenomena. A huge SEP event increases
the radiation dose received by aircrews, who should be warned of such events as early as possible. We developed a warning
system for aviation exposure to SEPs. This article describes one component of the system, which calculates the temporal
evolution of the SEP intensity and the spectrum immediately outside the terrestrial magnetosphere.
Findings: To achieve this, we performed numerical simulations of SEP transport in interplanetary space, in whichinterplanetary SEP transport is described by the focused transport equation. We developed a new simulation code to solve
the equation using a set of stochastic differential equations. In the code, the focusedtransport equation is expressed in a magnetic field line coordinate system, which is a
non-orthogonal curvilinear coordinate system. An inverse Gaussian distribution is
employed as the injection profile of SEPs at an inner boundary located near the Sun.
We applied the simulation to observed SEP events as a validation test.
Conclusions: The results show that our simulation can closely reproduce
observational data for the temporal evolution of particle intensity. By employing thecode, we developed the WArning System for AVIation Exposure to Solar energetic
particles (WASAVIES).

Keywords: Solar energetic particles; Interplanetary particle transport; Radiation
dose; Numerical simulation; Warning system

Figure 1*Corresponding author: Yûki Kubo, kubo@nict.go.jp

13

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Contents
Extremely severe space weather and geomagnetically induced currents in regions with locally heterogeneous groundresistivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shigeru Fujita, Ryuho Kataoka, Ikuko Fujii, Antti Pulkkinen and Shinichi Watari
Statistical properties of superflares on solar-type stars based on 1-min cadence data
. . . . . . . . . . . . Hiroyuki Maehara, Takuya Shibayama, Yuta Notsu, Shota Notsu, Satoshi Honda, Daisaku Nogami and Kazunari Shibata
Regional-scale high-latitude extreme geoelectric fields pertaining to geomagnetically induced currents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Antti Pulkkinen, Emanuel Bernabeu, Jan Eichner, Ari Viljanen and Chigomezyo Ngwira
Assessing the hazard from geomagnetically induced currents to the entire high-voltage power network in Spain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Joan Miquel Torta, Santiago Marsal and Marta Quintana
Reproducing electric field observations during magnetic storms by means of rigorous 3-D modelling and distortion
matrix co-estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Christoph Püthe, Chandrasekharan Manoj and Alexey Kuvshinov
Observed geomagnetic induction effect on Dst-related magnetic observations under different disturbance intensitiesof the magnetospheric ring current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dan Xu, Huaran Chen and Mengtan Gao
Sensitivity of geomagnetically induced currents to varying auroral electrojet and conductivity models. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ciarán D Beggan
Observatory geoelectric fields induced in a two-layer lithosphere during magnetic storms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Jeffrey J Love and Andrei Swidinsky
The characteristics of geoelectric fields at Kakioka, Kanoya, and Memambetsu inferred from voltage measurements
during 2000 to 2011 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ikuko Fujii, Takashi Ookawa, Shingo Nagamachi and Takeshi Owada
What caused the rapid recovery of the Carrington storm? . . . . . . . . . . . . . . . . . . . Kunihiro Keika, Yusuke Ebihara and Ryuho Kataoka
Estimation of geomagnetically induced currents based on the measurement data of a transformer in a Japanese power
network and geoelectric field observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shinichi Watari
Estimating the solar wind conditions during an extreme geomagnetic storm: a case study of the event that occurredon March 13–14, 1989 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tsutomu Nagatsuma, Ryuho Kataoka and Manabu Kunitake
Records of sunspot and aurora during CE 960–1279 in the Chinese chronicle of the Sòng dynasty. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hisashi Hayakawa, Harufumi Tamazawa, Akito Davis Kawamura and Hiroaki Isobe
Compilation of 3D global conductivity model of the Earth for space weather applications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dmitry Alekseev, Alexey Kuvshinov and Nikolay Palshin
Historically largest geomagnetic sudden commencement (SC) since 1868 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tohru Araki
Global MHD simulation of magnetospheric response of preliminary impulse to large and sudden enhancement of
the solar wind dynamic pressure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Yasubumi Kubota, Ryuho Kataoka, Mitsue Den, Takashi Tanaka, Tsutomu Nagatsuma and Shigeru Fujita
Statistical analysis of extreme auroral electrojet indices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Masao Nakamura, Asato Yoneda, Mitsunobu Oda and Ken Tsubouchi
Frequency distributions of magnetic storms and SI+SSC-derived records at Kakioka, Memambetsu, and Kanoya. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Yasuhiro Minamoto, Shigeru Fujita and Masahiro Hara
Numerical studies of geomagnetically induced electric field on seafloor and near coastal zones incorporated withheterogeneous conductivity distributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tada-nori Goto
Interplanetary particle transport simulation for warning system for aviation exposure to solar energetic particles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Yûki Kubo, Ryuho Kataoka and Tatsuhiko Sato

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Cover image: Araki, T., Earth, Planets and Space 2014, 66:164 DOI: 10.1186/s40623-014-0164-0