Sun and Geosphere, 2011; 6(2): 67 - 72

ISSN 1819-0839

A study of latitudinal dependence of Pc 3-4 amplitudes at 96º magnetic
meridian stations in Africa
E. M. Takla1, K. Yumoto1,2, M. G. Cardinal1, S. Abe2, A. Fujimoto3, A. Ikeda2,
T. Tokunaga1, Y. Yamazaki1, T. Uo-zumi2, A. Mahrous4, E. Ghamry4,5, G. Mengistu6,
T. Afullo7, A. Macamo8, L. Joao8, H. Mweene9, N. Mwiinga9, C. Uiso10, P. Baki11, G.
Kianji11, K. Badi12, P. Sutcliffe13, P. Palangio14
1

Department of Earth and Planetary Sciences, Kyushu University, Japan;
2
Space Environment Research Center, Kyushu University, Japan;
3
Institute of Space and Astronautical Science, JAXA, Japan;
4
SWMC, Helwan Univ., Egypt;
5
NRIAG, Helwan, Egypt;6Dept. of Phys. Addis Ababa Univ., Ethiopia;
7
Dept. of Elec. Engineering Univ. of Kwazulu-Natal, South Africa;
8
Dept. of Phys., Eduardo Mondlane Univ., Mozambique;9
Dept. of Physics, Univ. of Zambia;
10
Dept. of Phys., Univ. of Dar es Salaam, Tanzania;
11
Dept. of Phys., Nairobi Univ., Kenya;
12
Dept. of Eng., Sudan Univ. of Sci. and Tec., Sudan;
13
Hermanus Mag. Observatory, South Africa;
14
Istituto Nazionale Geofisica Vulcanologia (INGV), Italy.
E mail (takla@serc.kyushu-u.ac.jp & emad_serc@yahoo.com).
Accepted: 14 September 2011

Abstract.The study of latitudinal dependence of Pc 3-4 amplitudes at very low latitudes particularly near the dip equator isvery important to identify the propagation mechanisms of the equatorial Pc 3-4 pulsations. Therefore, geomagnetic data
simultaneously recorded at the MAGDAS African stations along the 96º Magnetic Meridian chain were analyzed to examine thelatitudinal dependence of Pc 3-4 amplitudes at the equatorial and very low latitudes up to middle latitudes. During three anda half months between 4 October 2008 and 22 January 2009, 21 Pc 3 events and 25 Pc 4 events were selected for studying
the latitudinal dependence of Pc 3-4 amplitudes. The latitudinal profile of the Pc 3 amplitude ratio indicates attenuation in
the Pc 3 amplitudes at the dip equator. This attenuation may be due to the ionospheric shielding effect. On the other hand,
the Pc 4 amplitude shows a peak at dip equator and decreased with increasing latitude up to middle latitudes as it revealed
from the latitudinal profile of the Pc 4 amplitude ratio. According to the obtained results, the main source of the equatorialPc 3 must be related to the compressional upstream waves, while the equatorial Pc 4 may be linked with the compressional
upstream waves and/or the Pc 4 excited at higher latitudes.
© 2011 BBSCS RN SWS. All rights reserved
Keywords: Latitudinal dependence, Equatorial Pc 3-4, Pc 3-4 amplitudes, Shielding effect.

Introduction
Geomagnetic pulsations, Ultra Low Frequency (ULF)
waves, are naturally occurring magneto-hydrodynamic(MHD) waves in the Earth's magnetosphere. These ULF
waves are classified as continuous (Pc) or irregular (Pi)pulsations. Each category is subdivided into period
bands that roughly separate a specific type of pulsation.
Pc 3-4 pulsations are continuous geomagnetic
oscillations with a quasi-sinusoidal waveform. These two
types of continuous pulsations are relatively low
amplitude fluctuations of the geomagnetic field withperiods of 10-45 s (Pc 3 range) and 45-150 s (Pc 4 range)[1-3]. The amplitude of the Pc 3-4 pulsations [peak topeak] ranges from fraction of a nano Tesla (nT) to a few
nT. The characteristics of ULF waves observed on the
ground contain information not only about thegeneration processes but also about the regions
through which they have propagated [4].

Most of the ULF wave studies have relied on dataobtained from middle or high latitudes, while theequatorial and very low latitudes have received a little
attention[5].
Consequently,
thesourceandpropagation mechanisms of the equatorial and very
low latitude pulsations are not fully understood and theymight be related to either upstream waves or themechanisms of pulsations at higher latitudes [2, 5]. A
number of studies indicated an attenuation of the Pc 3
amplitude at the equatorial region [6-8]. On the other
hand, some studies at the equatorial region showed anenhancement in the Pc 3 amplitudes at dip equator [911]. However for short period Pc 3 pulsations (< 20 s), theequatorial Pc 3 amplitude has been reported to suffer
attenuation rather than amplification [9].
The study of the latitudinal dependence ofgeomagnetic pulsations at very low latitudes particularly
near the dip equator is very important to identify the
propagation mechanism of the low-latitude pulsations,67E.M. Takla et al, A study of latitudinal dependence of Pc 3-4 amplitudes at 96º magnetic meridian stations in Africai.e., a direct incidence of the compressional waves on
the equatorial ionosphere or a leak of the ionosphericcurrent caused by the pulsations at higher latitudes. The
latitudinal dependence of the geomagnetic pulsations
can be studied by a meridional array of stations. In thepresent
study,
we
investigate
thelatitudinal
dependence of Pc 3-4 amplitudes at equatorial to
middle latitudes using simultaneous geomagnetic
observations across the dip equator through theMAGnetic Data Acquisition System (MAGDAS) at
African stations in order to identify the generation andpropagation mechanisms of the equatorial Pc 3-4.
Instrumentation and data acquisition
MAGDAS Project effectively started in May 2005, with
the installation of the first MAGDAS magnetometer in
Hualien, Taiwan [12-13]. Since then, over 50
magnetometers have been installed around the world.
They are distributed along three chains: (1) The 210º
Magnetic Meridian (MM) chain, (2) The dip Equator
chain, and (3) The 96º MM chain (African chain) as
shown in Figure 1.
MAGDAS system is composed of two subsystems,
which are MAGDAS-A and MAGDAS-B. MAGDAS-A
consists of the magnetometer, data logger and datatransfer modules. Magnetic field digital data are
obtained with the sampling rate of 1 second, and thenthe recorded data are transferred from the overseas
stations to Space Environment Research Center (SERC),
Japan in near real-time. Also, the data are recorded incompact flash memory cards in situ. MAGDAS-B is asubsystem of the MAGDAS to receive the data fromMAGDAS-A, analyze the MAGDAS data and monitor the
analyzed data as well as the status of each overseas
station. The complete system of MAGDAS-B was installedat the SERC, Kyushu University in December 2004 [12].
The geomagnetic data used in this study wererecorded using 2 types of magnetometers: MAGDAS
and MAGDAS II magnetometers. MAGDAS system was
manufactured by Meisei Electric Co., Ltd., while
MAGDAS II system was developed by SERC, Kyushu
University. Both types of magnetometer are ring coretype fluxgate magnetometers that can measure evensmall-amplitude geomagnetic fluctuations.
TABLE 1:
The geomagnetic stations selected for the present study.
Abbrev

StationG. Lat

G.
Long

GM.
Lat

GM.
Long

LAQ

L’Aquila

42.38

13.32

36.25

87.56

FYM

Fayum

29.3

30.88

21.13

102.38

ASW

Aswan

23.59

32.51

15.20

104.24KRT

Khartoum

15.33

32.32

5.69

103.8

AAB

A Ababa

9.04

38.77

0.18

110.47

NAB

Nairobi

-1.16

36.48

-10.65108.18DES

Dar Es Salam

-6.47

39.12

-16.26110.59LSK

Lusaka-15.2328.20-26.0698.32

MPT

Maputo-25.5732.36-35.9899.57

DRB

Durban-29.4930.56-39.21

96.1

HER

Hermanus-34.3419.24-42.2982.2

68Fig. 1: African MAGDAS stations used in the present study.

The sensitivities of both types are almost the same witheach other and also share the same sampling rate (1 s).
Three observation ranges of ±2,000 nT, ±1,000 nT, and ±300 nT can be selected for high, middle, and lowlatitudestations, respectively. The resolutions of MAGDAS
data are 0.061 nT/LSB and 0.031 nT/LSB, and 0.0091
nT/LSB for ± 2,000 nT, ± l,000 nT, and ± 300 nT range,
respectively [2]. The noise level of the MAGDAS andMAGDAS II magnetometer is 0.02 nT.
Data analysis and results
Since the main goal of the present study is to
examine the latitudinal behavior of Pc 3-4 amplitudes,
we analyzed one second geomagnetic data from 96º
MM stations located from the dip equator to the middle
latitudes. This profile extends from L' Aquila (LAQ) in Italy
down to Hermanus (HER) in South Africa as shown in
Figure1. Table 1 shows the geographic andgeomagnetic coordinates (AACGM) of the MAGDAS
stations along the studied profile. This profile includes 11
MAGDAS stations (four MAGDAS stations: LAQ, FYM, AAB
and HER; seven MAGDAS II stations: ASW, KRT, NAB, DES,
LSK, MPT and DRB). Geomagnetic data obtained from
the MAGDAS magnetometer at LAQ station (Italy,
Europe) were used to extend the latitudinal profile in thenorthern direction. The geomagnetic data used for thisstudy were recorded from 4 October 2008 up to 22
January 2009.
The selection of the Pc 3-4 events involved
comparing the daily dynamic power spectra of the Hcomponent recorded at each station. The dynamic
power spectra were performed in the period range 10150 s by using MATLAB scripts in order to identify the Pc
3-4 events. Each day of geomagnetic data includes
86400 points, which subdivided in segments with 512
points. The dynamic spectra were calculated by thesliding Fast Fourier Transform (FFT) technique (512 pointsof 1-s resolution, sliding by 5 minutes). A clear peak inthe dynamic power spectrum diagrams (visualSun and Geosphere, 2011; 6(2): 67 - 72

inspection) in the same frequency range at each station
and a continuous quasi-sinusoidal waveform in bandpass filtered (20-40 s for Pc 3 and 70–100 s for Pc 4)
geomagnetic data recorded at each station were theselection criteria for the Pc 3-4 events. The selected Pc
3-4 events were observed along the selected profile
with a good visual similarity (in dynamic power spectra)
and coherence (in the waveform of the band-passfiltered data), except for DRB station where the data
were too noisy and thus excluded from our results. Also
KRT station was a bit noisy compared with other stations,but the difference in noise level was not too great towarrant exclusion. The ratio of noise level between KRT
and AAB (KRT/AAB) stations was about 1.15. Figure 2
presents two hours (0800-1000 UT) dynamic power
spectra (period range 10-150 s) of the H component
recorded on 4 October 2008 at some African stations,where the H component shows an enhancement in the
wave amplitude in the spectral band of 20-150 s andalso the dynamic power spectra were visually similar
along these stations.
Twenty one pulsation [Pc 3] events were selected forstudying the Pc 3 amplitudes, and 25 [Pc 4] events wereselected for the Pc 4 amplitudes along the same profile.
The selected events occurred in the daytime from 0600
up to 1800 LT. The duration of the pulsation events was
not constant; some events lasted for several minutes
while other events lasted for one hour or more. In somepulsation events, it was difficult to find a goodcorrelation between a number of the selected stations
because some of these stations had momentarily noisy
data (perhaps related to human activities near thesestations). Therefore, we excluded such events from ourresults.
To examine the Pc 3 amplitudes for the selected
events, the H (North-South) and D (East-West)
components were digitally band-pass filtered in two
period ranges: 20-30 s and 30-40 s (Pc 3 range). Figure 3
shows the filtered wave packets obtained after
applying the two above-mentioned band-pass filters on
one hour data of the H component from 0800-0900 UT
on 4 October 2008 along a profile represented bystations code. Each event was divided into segments of
10 minutes length, and then the average peak-to-peakamplitude for each segment was determined. In thenext step, the average Pc 3 amplitude was calculated
for the whole pulsation event. After that, we calculated
the Pc 3 amplitude ratio at each station in reference to
AAB station (LAQ/AAB, FYM/AAB .... HER/AAB). Finally,
we constructed the latitudinal profile of the Pc 3
amplitude ratios (Figure 4a and b). For the H component,
there was a distinct latitudinal variation. The Pc 3
amplitude showed an enhancement at low latitude
stations but with a depression at the dip equator (AAB
station) and then it decreased steadily with increasing
station latitude (up to ≈ ± 25º). At higher latitudes, it
increased with increasing latitude. It is noteworthy thatthe attenuation of the shorter-period Pc 3 (20-30 s)
amplitude at the dip equator is larger than the longerperiod Pc 3 (30-40 s) as shown in Figure 4 a and b,
respectively. On the other hand, the D component Pc 3
pulsations behaved differently. The amplitude was
generally less than that of H component (i.e. the Pc 3

ISSN 1819-0839

Fig. 2: Dynamic power spectra of two hours (0800-1000 UT)
data of H component recorded at some MAGDAS African
stations on 4 October 2008 [band pass filter 10-150 s].

Fig. 3: A pulsation event in H component recorded at some
African stations on 4 October 2008; the data have been
digitally filtered in both 20-30 s and 30-40 s periods
band, panels A and B respectively.

amplitude ratio D/H at AAB station was ranging
between 0.25-0.3) and there was no systematic
variation with latitude.
The band-pass filter in the period range 70-100 s wasapplied on the H and D components of the selected Pc
4 events. Figure 5 shows the filtered wave packets
obtained after applying the band-pass filter (70-100 s)
on two hours data of the H component from 0900-1100
UT on 4 October 2008 along a profile represented bystations code. The Pc 4 amplitudes were measured using
the same technique previously used in the case of Pc 3.
After that, we constructed the latitudinal profile of the
Pc 4 amplitude ratios (by using the same procedure forcalculating the amplitude ratio of the Pc 3 pulsations),
which showed a peak at the dip equator and thendecreased with increasing latitude (up to middle
latitudes) as shown in Figure 6. Similarly to the Pc 3, the Dcomponent Pc 4 amplitudes were much smaller thanthe H component Pc 4 amplitudes (i.e. the Pc 4
amplitude ratio D/H at AAB station was around 0.35).
Discussion
Studies of the ULF waves at low latitudes show thatsignificant hydromagnetic wave energy penetrates
deep into the magnetosphere and the plasmasphere[14]. Generally, two models are proposed for thegeneration and the propagation mechanism of the Pc
3-4 at the equatorial region. The first model is the69

E.M. Takla et al, A study of latitudinal dependence of Pc 3-4 amplitudes at 96º magnetic meridian stations in Africa

compressional upstream waves model (model 1).
According to this model, the compressional waves
propagating along the magnetosphere (directtransmission from the magnetosheath across thedayside magnetosphere) arrive at the equatorial
ionosphere and couple with the magnetic perturbations
on the ground through the ionosphere [15-17]. In thiscase, the field line resonances will be excited by thecompersional waves; which are believed to be a main
source of Pc3 pulsation observed at low latitudes [18-20].
The ionospheric current model (model 2) is the second
model suggested to explain the propagation
mechanism of the equatorial Pc 3-4. In this model, thesurface waves generated by the Kelvin-Helmholtz
instability at the dayside high-latitude magnetosphereboundary generate large-scale ionospheric current
oscillations. These oscillations leak to the low latitude
and generate Pc 3-4 pulsations near the dip equator[2,16]. In model 1, attenuation of the pulsations
amplitude at the dip equator occurs as a result of theshielding effect, while an equatorial enhancement of
the pulsations amplitude occurs due to theconcentration of the ionospheric current to themagnetic equator in model 2 [21,16].
An attenuation of the Pc 3 amplitude at theequatorial region due to the shielding effect wasreported through many studies [6-7]. On the other hand,some studies indicated an equatorial enhancement of
Pc 3-4 amplitudes [9,11]. [9] observed an equatorial
enhancement of Pc 3-4 with periods greater than 30 s.
Also, they indicated attenuation in the Pc 3 amplitude
at the dip equator with periods less than 20 s. They
related such attenuation to the effect of the equatorial
ionosphere, where the ionosphere has a major role inthe modification of the pulsation properties during theirpropagation through the magnetosphere-ionospheresystem. However, their results did not refer to the
behavior of the Pc 3 amplitude in the period range 2030 s at the dip equator. Moreover, their results
depended on data obtained from two stations only.
In the current study we analyzed data obtained froma meridional magnetometer array distributed over awide range of latitudes; from dip equator up to middle
latitudes. From the obtained results concerning the Pc 3,
we found that the Pc 3 amplitudes show a peak at lowlatitude stations with a depression at AAB station (thedip equator). Moreover, the attenuation in the Pc 3
amplitude is larger in the period range 20-30 s (typicalrange for the upstream waves) than that in the period
range 30-40 s as shown in Figure 4.
This attenuation of the Pc 3 amplitude can be linked
with the ionospheric conductivity above the dip
equator. The very low latitude region is characterized byhigh zonal ionospheric conductivity close to the dip
equator and the induced ionospheric currents aremainly controlled by the intensity of the ionosphericconductivity.
We consider that the equatorial Pc 3s observed on
the ground are generated by model 1, in this case, thepropagating compressional waves (that originallygenerated in the region upstream of the bow shock) areprevented from passing to the atmosphere by the
induced ionospheric currents, i.e. these currents act as

70

an obstacle in thecompressional waves.

way

of

the

propagating

Fig. 4: The latitudinal profile of the Pc 3 amplitude ratios(the solid curve represents the average amplitude ratiosof the Pc 3 for the selected events). Panel (a) is for the
Pc 3 (20-30 s) and panel (b) is for the Pc 3 (30-40 s).

Fig. 5: A pulsation event in H component recorded at some
African stations on 4 October 2008, the data have been
digitally filtered in the (70-100 s) period band.

Fig. 6: The amplitude ratio profile of Pc 4 (70-100 s)
pulsations (the solid curve represents the average
amplitude ratio of the Pc 4 for the selected events).

As a result, we can observe attenuation of thepulsation amplitudes. Besides, the observed attenuationof the Pc 3 amplitude was larger in the period range 2030 s, which is the typical range for the compressional
upstream waves. So the concept of shielding effect of
the high-conducting equatorial ionosphere is anacceptable theoretical concept to interpret theattenuation of the Pc 3 amplitude at the dip equator [67].
In our opinion, the reason that the attenuation of Pc
3s amplitude in the period range 20-30 s is larger thanthat in the period range 30-40 s (see Figure 4), may be
due to the superposition of the Equatorial Electrojet (EEJ)

Sun and Geosphere, 2011; 6(2): 67 - 72

effect on the shielding effect. The EEJ, an eastward
electric current in the day time equatorial region of the
Earth's ionosphere, has a considerable influence on
geomagnetic variations over a wide range of periods[9]. The EEJ effect can cause an enhancement in thesignal amplitudes of the Pc 3-4 close to the dip equator[22].
[8] reported that the lower frequencies ofmagnetic
pulsation
undergolargerequatorial
amplification due to the EEJ effect, but for a certain
frequency range (18-24 s) the pulsation signal is found toattenuate rather than exhibit the general enhancement.
However no specific explanation was given for suchattenuation in their study.
Therefore, we propose that the daytime equatorial
Pc 3s observed at the African sector are propagatedfrom the upstream region by the compressional wave
model. In addition, it is difficult to explain theoccurrence of very low-latitude Pc 3 on the ground as aresult of the surface waves (model 2) at the day sidehigh-latitude magnetopause because of the highdamping rate of these wave in the Pc 3 frequency
range in the radial direction (for more details see [23,2]).
Furthermore, [24] demonstrated a high coherence
between the compressional component in space andthe H component on the ground after they performed acoherence analysis of a Pc 3 event observed both inspace (by a satellite) and on the ground.
On the other hand, the Pc 4 amplitudes showed apeak at dip equator and decreased with increasing
latitude up to middle latitudes. As for the equatorial Pc 4,
there are not so many studies related to the Pc 4 at theequatorial
regionbecausemost
researchers
concentrated on mid to high latitudes. In our results
concerning the equatorial Pc 4, we found a peak at the
dip equator in contrast to the Pc 3. However, the sourceof the equatorial Pc 4 is not fully understood, but the two
above-mentioned models can be used to explain thegeneration mechanism of the equatorial Pc 4. If weconsider the compressional upstream waves as a sourceof the equatorial Pc 4; In this case, the Pc 4 amplitude atthe dip equator will not attenuated due to shielding
effect because the shielding effect attenuation mainly
occurs in the shorter-period pulsations (Pc 3 range). On
the other, if we consider the source of the equatorial Pc
4 is the leak of the ionospheric currents caused by the
Pc 4 pulsations at higher latitudes (model 2), we canobserve an enhancement in the Pc 4 amplitudes at the
dip equator as it reported by [16]. Many studies showedthat there is enhancement of equatorial Pc 5 whose
main source is at high latitudes [25-26], so maybe we
can expect a similar mechanism for generating theequatorial Pc 4 pulsation. In our opinion, more detailed
studies are required in order to examine that exact
source of the equatorial Pc4 (including the phasedifference, coherence, polarization etc).
It is well known that the occurrence and intensity ofgeomagnetic
pulsationsarelinkedwiththeinterplanetary magnetic field (IMF) and the solar windvelocity (V) as revealed from many geomagnetic
observations (ex. [27]). Furthermore, the upstream
waves are generally controlled by the solar windparameters and the IMF. The transmission of upstream
waves into the Earth's magnetosphere can be linked

ISSN 1819-0839

with the cone angle (the angle between the IMF and
the Sun-Earth direction). Previous studies showed that,the transmission process will be better under small valuesof cone angel [27-28]. Hence, we examined the solar
wind velocity, the IMF magnitude and the cone angle
during the selected Pc 3-4 events in order to confirm thesource of the equatorial Pc 3-4 pulsations. Figure 7 shows
the comparison of the dynamic power spectrum of the
H component recorded at AAB station (panel [a]), andthe total magnitude of the IMF (panel [b]), the coneangle (panel [c]) and the solar wind velocity (panel [d])in the upstream region during 13 October 2008 (UT). The
IMF and Solar wind velocity data are obtained from theAdvanced Composition Explorer (ACE). We found,
about 85% of the Pc 3 events and 60% of the Pc 4
events occurred during solar wind velocity ranging
between 400-650 km/s. Furthermore, we found that the
shorter period of the magnetic pulsation (Pc 3) tend tooccur during IMF magnitude ranging between 4-6 nT.
While, the longer period (Pc 4) pulsations occur during
low IMF magnitudes (less than 2.5 nT).
These observations agree with the formula proposedby [23] concerning the interrelation between the IMF
magnitude and the frequency of the magnetic
pulsations observed on the ground. In addition, 80%
from the Pc 3-4 events occurred during cone angle lessthan 45°. From these results, the occurrence of theequatorial Pc 3s can be correlated with the upstream
activities, which support model 1 to be the predominantsource of the equatorial Pc 3. In addition, Pc 4s showed
less correlation; in this case, models 1 and 2 almost haveequal possibilities to be the source of the equatorial Pc 4.

Fig. 7: The comparison of the dynamic power spectrum of the
H component recorded at AAB station (panel [a]), and thetotal magnitude of the IMF in nT (panel [b]), the coneangle in degrees (panel [c]) and the solar wind velocity in
km/s (panel [d]) at the upstream region during 13
October 2008 (UT).

Summary and conclusion
Based on 46 magnetic pulsation events (Pc 3-4)
observed at selected MAGDAS African stations along
96° magnetic meridian array during three and a halfmonths starting from 4 October 2008, we studied the
behavior of Pc 3-4 amplitudes at equatorial and low
latitude stations. We identified the Pc 3-4 pulsation
events by constructing the dynamic power spectra forthe data recorded at each station. The Pc 3-4
amplitudes were calculated after applying the bandpass filters for both H and D components. From the71

E.M. Takla et al, A study of latitudinal dependence of Pc 3-4 amplitudes at 96º magnetic meridian stations in Africa

statistical analysis of our results, we obtained thelatitudinal profiles of the Pc 3-4 amplitude ratios.
The latitudinal profile of the Pc 3 amplitude ratio
indicates attenuation in the Pc 3 amplitudes at the dip
equator. This attenuation may be due to the ionosphericshielding effect. On the other hand, the Pc 4 amplitude
shows a peak at dip equator and decreased withincreasing latitude up to mid latitudes as it revealed
from the latitudinal profile of the Pc 4 amplitude ratio.
According to the obtained results, the main source ofthe equatorial Pc 3 must be related to thecompressional upstream waves, while the equatorial Pc
4 may be linked with the compressional upstream waves
and/or the Pc 4 excited at higher latitudes. These results
agree with the model of the excitation and propagationof MHD waves leading to Pc 3-4 activity on the Earth's
surface proposed by [15].
Acknowledgments
The first author is very grateful to the Egyptian Government,
Ministry of Higher Education for granting him a scholarship to do
his Ph.D studies at Kyushu University, Japan. The authors would
like to thank the MAGDAS Group for their ceaseless support ofthe observation and providing the geomagnetic data.
MAGDAS II Project was financially supported by Japan Society
for the Promotion of Science (JSPS) as Grant-in-Aid for Overseas
Scientific Survey (18253005). Moreover, we thank the ACE MAG
and SWEPAM instrument teams and the ACE Science Centerfor providing the ACE data.

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