Terminator effects and dayside ionosphericcurrent system on Pi2 pulsations

Imajo Shun1), Akimasa Yoshikawa2)1), Teiji Uozumi2), Shinichi Ohtani3) ,Aoi Nakamizo4) , Peter J. Chi5)1) Department of Earth and Planetary Science, Kyushu University
2) International Center for Space Weather Science and Education, Kyushu University
3) Johns Hopkins University Applied Physics Laboratory4) Corporate Planning Department, National Institute of Information and Communications Technology
5) Earth Planetary and Space Sciences, University of California

Figure 7. It is obviousthat the DP 2 fluctuationsis strongly
confinedto the region above60ø and decreasesmonotonously
at midlatitudeand low latitude,while it is stronglyenhancedat
the equatorialstations.In the caseof the peak at 1300UT, themagnitudebeing 103 nT at 71ø decreasesto 41 nT at 57ø, andto 7 nT at low latitudes,but increasesagainto 22 nT at Mokolo(1400 LT) and 37 nT at Sao Luiz (tOO0LT). The equatorial

磁気圏起源擾乱の赤道強化現象

50SaoLuiz.__

Pi2地磁気脈動を含む多くの磁気圏起源の擾乱•,----•.••..,•/•,•• Eusebio(DP2, Pc5, SCなど)は昼間側磁気赤道で振幅が増す._.

enhancement

u.........

12I .........

I .........

I .........

131415is about

3 in Africa

and 4 in Brazil.

Itshouldbe notedthat the magnitudeof the DP 2 fluctuationsat
the dip equator are almostcomparableto that at subauroral
latitudes.Tsunomuraand Araki [1984] calculatedglobalelectric field and current by assumingthe realisticionosphericconductivityand the region t current flowinginto and out of0-50

ratio

16Time JUT]H

0of Sao Luiz.

-2210ou[] 1218 UT•........
./x
1300
UT..

•50n• SaoLuiz"'%.
.....

Santa Maria is 4.0. On the other hand, the ratios of the diurnal/•.•Mokolo

0-1-221H0-102000210

昼側磁気赤道magneticvariation at Sao Luiz to Eusebioand to Belem on aorelativelyquiet day (E Kp = t0 on April 28, 1993)is 1.4 and8o60
40200-20
1.7, respectively.The enhancementratio of the DP 2 fluctuaCorrectedGeomogneticLotifude[deg]tions is larger thanH that of the diurnal variation, but it is Figure 7. Latitudinalprofilesof the magnitudeof the DP 2
apparent that the equatorial enhancementof the DP 2 flucfluctuationsrecordedon April 20, 1993, at the IMAGE statuations is caused by the concentrationof the ionospherictions and the European and African chain stations.Two procurrent which is due primarily to the enhancedionospheric filesare depictedfor the peaksat 1218and 1300UT with solidconductivity.
anddashedcurves,respectively.
The magnitude(a)
Amplitude
ratio at SaoLuiz is
It is worthwhileto point out that the Z componentnega- also plotted
equatorial40
enhance0 to indicate
10 the remarkable
2030
G.M. latitude
tivelycorrelateswith the H componentat SaoLuiz and Belem, ment3 at the dip equator.Here the magnitudeis comparabletowhilethe relationispositiveat Eusebio(Figure6b). Thisresult that at subauroral latitudes.

1hhmm
2012 Mar 26

a...•componentat Eusebiois in the oppositesenseto that at othertwo stations,indicatingthat the electrojetflowsslightlysouth

-1-2

150

Sao Luiz as at other stations, and the fluctuations in the Z

Wed Oct 22 16:06:39 2014

ASB
L= 1.6
MLT=11.3hr[nT]

DP 2 variation Js enhancedat all three equatorial stations
comparedto the low-latitudestation(seetext). Among thesestations,the magnitudeof the H componentis twiceaslargeat

昼側低緯度BCL
L= 1.0
MLT= 8.9hr
[nT]

1

夜側FRD
L= 2.4
MLT=20.9hr[nT]

Figure 6. DP 2 fluctuationsobservedon April 20, 1993, at
典型的なPi2の波形
the Brazilian equatorial stations,Belem, Sao LuJz, and Euse2
bio on the (a) H and (b) Z component.The magnitudeDP2of theKikuchi et al. [JGR,1996]

Pi2地磁気脈動

032I'I,

no10i--

10(b)z•mo3

Phase difference(b)Shinoharaet al. [GRL,1997]

夜側起源のPi2がどのようにして伝わり昼間側赤道に大きな振幅をもたらすか?
010203040 G.M. latitude

0J30I10'I昼間側Pi2と電離圏電流
過去の研究では、昼間側地上低緯度のH成分磁場は極域電場の侵入による東西の電離層電流振動が原因であると解釈される。

[Kikuchi and Araki,1979, JASTP; Shinohara et al.,1998, JGR]
昼夜境界=電気伝導道が急激に変化するところ電場の伝播 [Shinohara, 1998](e.g. 大気導波管 [Kikuchi and Araki, 1979])
オーロラ嵐に伴う電流振動ソース
日陰領域(very low conductivity)

日射領域(high conductivity)
磁気赤道日射領域(very high conductivity)

昼夜境界

高伝導度領域で強化された電離圏電流

日射領域のPi2が電離圏電流が関与していれば朝夕昼夜境界付近でなんらかの変化が見られるはずSunrise effect on Pi2 and Pc4 range wave
darknesssunlight

Criticalfrequency

ASO H
H is comparable with D

H is larger than D
ASO D

LT at ASO

Saka et al. [JASTP, 1980]

複数観測点での同時観測はでは未だ検証されていない。

Imajo, S., A. Yoshikawa, T. Uozumi, S. Ohtani, A. Nakamizo, R.
Marshall, B. M. Shevtsov, V. A. Akulichev, U. Sukhbaatar, A.
Liedloff, and K. Yumoto (2015), Pi2 pulsations observed aroundthe dawn terminator. J. Geophys. Res. Space Physics, 120, 2088–2098. doi: 10.1002/2013JA019691.

quadrant, while those in the sunlit Northern H
in the northeast quadrant. The major axes rot
Hemisphere and counterclockwise in the Sou

朝側昼夜境界でのPi2 (21:50 UT on 16 September 2011)
H component (North-south)

D component (East-west)

100 km0 km

Figure 1. Map of the stations and the terminator a200 km
September 2011. The solid curves are the locations
three diﬀerent altitudes: 0 km (yellow), 100 km (redIMAJO ET AL.

©2015. American Geophysical Union. All R
Imajoet al. [JGR, 2015]

igure 2. (a) AL index, the (b) H component, and (c) D component magnetic variations around the dawn terminator at
1:50 UT on 16 September 2011. The arrow in Figure 2a indicates the timing of the Pi2 event. ΔTsr is the time diﬀerence
between the sunrise• time defined at 100 km in altitude and the event time, where negative values indicate that a station
was in darkness while positive values indicate that a station was in sunlight.

H成分はほぼ同位相。

•

昼夜境界付近を境にD成分の位相が反転する。

D oscillations at the sunlit stations (ASB and TWV) exceeds those of the H oscillations in all the events. The H
日陰、日射領域共に、南北半球でD成分の位相が反転する。
oscillations are in•phasein each event. On the other hand, all events show an antiphase relationship of theD oscillations between HVD and ASB in the Northern Hemisphere and between LRM and DAW in theSouthern Hemisphere.

朝側昼夜境界でのPi2 (その他の例)
relative location of stations
D-component oscillations in the dark and sunlit
hemispheres were in antiphase, whereas the H
ASB
HVDcomponent oscillated in phase.
equatorAt the sunlit stations (ASB, TWV), D-component
amplitudes were larger than the H-component amplitudes.
LRMTWV

4

HVD H

3

ASB H

2

LRM H

1

TWV H

0−16nT5

D comp3
2.5

24−Sep−2011 20:47:00

2.5

H comp

2

HVD H

1.5

ASB H

1

LRM H

0.5

TWV H0−0.532.5

D comp

HVD D

2

HVD D

3

ASB D

1.5

ASB D

2

LRM D

1

LRM D

1

TWV D

0.5

TWV D−12050

02055
2100
UT[hhmm]

2105

−0.5
2040

2045
2050
UT[hhmm]2055

08−Sep−2011 21:07:00

H comp

HVD H

1.5

ASB H

1

LRM H

0.5

TWV H

02.5

402nT

H compSouthern hemispherenT502−Oct−2011 20:57:00

Event CD comp

2

HVD D

1.5

ASB D

1

LRM D

0.5

TWV DnT

6dawn terminator

Event B

Northern hemisphere

Event A

nT

•nT•

02100

2105
2110
UT[hhmm]

2115

Imajo et al. (2015, JGR)

統計解析 (位相反転のタイミング)
朝側ASBのD成分とそのとき夜側にあるTAMのH成分の位相差を計算した•

D成分の位相反転のタイミングはは地方時(b)よりむしろ日の出からの時刻(b)に従う。

•

D成分の位相反転は100km高度の昼夜境界の約0.5時間昼間側で起こる。
Longitudinal dependence of cross phase betweensunrise
ASB-Dtimeand TAM-H

cross phase [gedrees]270(b)

Dependence with sunrise reference time

180

180
900darkness

100

sunlight

500−3−2−101∆Tsr(ASB) [hour]-90º ≤ (cross phase) < 90º90º ≤ (cross phase) ≤ 270º

23900−90[%][%]−90−4Dependence with local time270

cross phase [gedrees](a)at the winter solsticesunrise timeat the winter solstice4100500123456LT(ASB) [hour]

78

Imajo et al. (2015)9夕方側昼夜境界付近のPi2
Journal of Geophysical Research: Space Physics•

日の入境界から約2-3時間昼間側でD成分の位相の反転が見られる•

位相の反転する経度から昼間側のD成分の振幅は非10.1002/2013JA0196

relative location of stations
HVD
equator

PPI
LZH

ASB

常に小さい

dusk terminator

Event D
23−Aug−2011 10:12:00

Event E
03−Sep−2011 10:02:00

Event F
05−Sep−2011 08:22:00

Imajo et al. [JGR, 2015]

昼夜境界付近のPi2の解釈
多点磁場観測を用いた等価電流分布から検証
大体こういうcurrent closureになっているはず

オーロラ帯

?

ASB (TWV)

dusk
電流の摂動
磁場の摂動

dawn
HVD (LRM)

カレントウェッジ振動モデル[Lester et al., 1983]

Pi2の等価電流の定義
水平成分に関して主軸に沿った変動のみに注目する
水平成分の磁場変動()の極大時に関して等価電流の方向をマッピングする
Equivalentcurrent
of Pi 2filt=[40range
ASB 2012/02/03
10:30:56 intarval=5min
150]

magnetic
perturbationof filt=[40Pi 2150]range
ASB 2012/02/03
10:30:56 intarval=5min

0.50.5

H [nT]

H [nT]

90°時計回りに回転
0−0.5−0.50D [nT]

0.5

電離圏電流

地上磁力計0−0.5−0.5

磁場変動

0D [nT]0.5

AL index, 昼間側Pi2の波形 (23:10 UT on 2 February 2012)
0Pi2 onset

AL index

0.4
0.2
0.0
1.00.80000
Feb 030100

H-comp

0.5

1.0
H

0.0
-0.5

0.4
0.2
0.0
1.0
0.8

0.5

H

0.0
-0.5

2310

2320

① ② ③ ④-0.5hhmm
2012 Feb 02

•
•
•

H

0.023102320

TUC
L= 1.7
MLT=14.8h
[nT]

0.5

-1.0

0.5
0.0

D-0.5

0.5

D0.0-0.5-1.0
1.0
Sun Aug 16 14:20:22 2015

0.4

午後TUC
L= 1.7
MLT=14.8h[nT]-1.01.00.6

D-comp-1.01.0

HON
L= 1.2
MLT=11.8h
[nT]

正午

HON
L= 1.2
MLT=11.8h
[nT]

-1.0
1.00.6hhmm
2012 Feb 02

ASB
L= 1.6
MLT= 8.1h[nT]

午前

Sun Aug 16 14:20:20 2015

ASB
L= 1.6
MLT= 8.1h[nT]
HON
L= 1.2
MLT=11.8h[nT]
TUC
L= 1.7
MLT=14.8h
[nT]

1.0

0.6

0.2
0.02300

AL

0.5
-0.5
-1.0

水平方向の振幅のピークはほぼ一致する
D/H振幅比は午前側が大きい

D0.0hhmm
2012 Feb 02

午前-午後でD成分の位相が反転

Sun Aug 16 14:20:25 2015

-150-200-250hhmm
2200
2012
Feb 02

1.00.8

Wed Mar 25 15:55:16 2015

-100

ASB
L= 1.6
MLT= 8.1h[nT]

Prov. AE
(1-min)
[nT]

-50

2310

2320

①

Equivalent currents at the first local maximum
90
60
30

90

120 150 180 -150 -120 -90

-60

-30

030

60

-30
1nT

2012-02-02/23:13:41

-60

-90
90 are directed• The meridional component of equivalent current vectors
equatorward in the prenoon sector and poleward in the postnoon sector.
60• The meridional component in the postnoon sector is smaller than in theprenoon sector.

Time variation of equivalent current①②906090603090

120 150 180 -150 -120 -90-60-30

030
30

6090

120 150 180 -150 -120 -90-60-30-30

2012-02-02/23:13:41

2012-02-02/23:14:18④60

120 150 180 -150 -120 -90-60-30

0

2012-02-02/23:15:11-60-9060

60
30

30

60

90

120 150 180 -150 -120 -90

-30
1nT

30-909030
9060-60

1nT-9090③30-30-60

1nT

0-60

-30

0-30

1nT

2012-02-02/23:15:52-60-90• 午前午後で赤道方向に出入りするような逆成分の南北成分電流が見られる• 午前側でより南北電流の卓越した非対称性が見られる• 電流系形状を維持したままPi2周期で振動している

ASB
L= 1.6
MLT= 6.8hr[nT]

Event 2 (2012-03-22/21:35:00)
2.0
1.5
1.0
0.5
0.0hhmm2012 Mar 22

210-1-2①②③ ④
2130

H-comp

2140

2130

90

①2140

2
10-1-2

D-comp
2130

2140

90

②60

60

30
120 150 180 -150 -120 -90-60

-30

030
30

60

90

120 150 180 -150 -120 -90

-60

-30

-30

2012-03-22/21:34:28

2012-03-22/21:34:54-30

0

2012-03-22/21:35:20

-60
-90

60

90

30
30

60

90

120 150 180 -150 -120 -90-30
1nT30

60

30
-60

90-90
90

④60

120 150 180 -150 -120 -9060-60

1nT-9090③30-30-60

1nT0-60-30

0-30

1nT

2012-03-22/21:35:45-60-90ASB
L= 1.6
MLT= 8.6hr[nT]

Event 3 (2012-03-02/23:35:00)
1.0
0.8
0.6
0.4
0.2
0.0hhmm2012 Mar 02①④③②2330

H-comp

1.0
0.5
0.0
-0.5
-1.0

2340

2330

90①2340

1.0
0.5
0.0
-0.5
-1.0

D-comp
2330

2340

90

②60

6030
90

120 150 180 -150 -120 -90-60-30

030
30

60

90120 150 180 -150 -120 -90-60-30-30

2012-03-02/23:33:28

2012-03-02/23:34:05④60120 150 180 -150 -120 -90-60-300

2012-03-02/23:34:40-60-90606030306090

120 150 180 -150 -120 -90-30
1nT30-909030
9060-60

1nT-9090③30-30-60

1nT

0-60-300-30

1nT

2012-03-02/23:35:14-60-90

variation at the ground will be more like the equivalentcurrent system which closes in the ionosphere.
Solid and dashed curves in the figure are thedemarcationlines for the reversal of the signs of the

電離層電流系の数値計算

1FIG .

Tsunomuraand Araki [PSS, 1984]
2. GLOBALDISTRIBUTIONOF
THE IONOSPHERIC CURRENTSFORTHEREALISTICCONDUCTIVITYMODEL.

The shaded zone is the source-current

Yoshikawa et al. [AGU fall meeting, 2012]

region.

昼間側Pi2の等価電流はdawnとduskにFACを置いた
時の昼間側電離圏電流系とゆがみ方がよく似ている

夜側に局在したFACでも同様の昼間側電離圏電流系が出来るのか?

Ionospheric current derived by global potential solver
We solve ionospheric potential
produced by fixed FACs ina similar frame work of Nakamizo et al. [2012]
We derive ionospheric current

fromand• Time-variable effects are negligible.
• Relative value of outputs does not depend on the magnitude of FACs.
• Conductivity tensor are calculated by the same method as Nakamizo et al. with input
parameters at the case study event. This method includes the modifications by auroral
precipitation [Hardy et al., 1987] and equatorial Cowling conductivity [Tsunomura, 1999].

downward

grid size : 514 (longitude) x 513 (latitude)(The grid size of the figure is reduced by 1/8)

upwardCalculated ionospheric current distribution※The upper range is smaller thanthe maximum value for visibility ofdayside current intensity

Upward FACHeight integrated current
density[(A/m2)*2.1*10^5]

Downward FAC

westward current• The zonal current reaches a peak at the equator because of higher
conductivities modified by the Cowling effect.
• The simulated dayside current system shows the prenoon-postnoon
asymmetry similar to equivalent current distributions of dayside Pi2.
• The order of the current density in the dayside low-latitude region isapproximately 1/100 of the current density in the nightside auroral region.

偏ったFAC配置の場合
対称な場合

夕方側寄り

朝方側寄り

• 昼間側で閉じる電流系の非対称性に対するFACの非対称性の依存は小さい• イベントごとのFACの構造は昼間側電流系にあまり影響しないと考えられる

Pi2のグローバル電流系による解釈
current perturbation
magnetic perturbation on the ground[nT]

auroral region

Sun Jul 5 14:58:53 2015

1HONTUC

20-1

DAVASB-22310hhmm
2012 Feb 02

ASB D
HON H
DAV H
TUC D

2320

DawnDusk• 真夜中、真昼、朝夕昼夜境界付近では逆向きに東西成分磁場変動が打ち消し合い位相が反転する。

Oscillatory FACs

Oscillatory current source• 午前-午後のD/Hの振幅比の違いはFACによって作られる電離圏電流の歪んだ構造から説明出来る。

END
Thank you for your attention
Acknowledgement:This work was supported in part by JSPS Core-to-Core Program, B. Asia-Africa Science Platforms and byGrant-in-Aid for JSPS Fellows (15J02300). MAGDAS/CPMN magnetic data were provided by theprinciple investigator of MAGDAS/CPMN project (http://magdas.serc.kyushu-u.ac.jp/). We thank thenational institutes that support INTERMAGNET for promoting high standards of magnetic observatory
practice (www.intermagnet.org). Magnetic data from KAK, CBI and, KNY are provided by JMA. We
acknowledge NASA contract NAS5-02099 and V. Angelopoulos for use of data from the THEMISMission. U.S. Geological Survey magnetometers: Original data provided by the USGS Geomagnetism
Program (http://geomag.usgs.gov). McMAC magnetometers: Peter Chi for use of the McMAC data and
NSF for support through grant ATM-0245139. We acknowledge the Inter-University Upper Atmosphere
Global Observation Network (IUGONET) project funded by the Ministry of Education, Culture, Sports,Science and Technology (MEXT), Japan.