平成26年度第2回STE現象報告会（Space Weather Event Report）(2015.3.4 Hotel Luigans)

GIC as a return current of theglobal ionospheric currents
during space weather
disturbances
T. Kikuchi(1), K.K. Hashimoto(2), S. Watari(3), Y. Ebihara(4)1: Solar-Terrestrial Environment Lab., Nagoya University
2: Kibi International University
3: National Institute of Information and Communications Technology
4: Research Institute for Sustainable Humanosphere, Kyoto University

Motivation and purpose
The midlatitude GICs are well correlated with the D-component magnetic
field [Watari et al., 2009] and are subject to diurnal and seasonal variations[Braendlein et al., JGR 2012]. The GIC has been suggested to be a return of
the ionospheric currents.

To understand the GIC in the ionosphere-ground current circuit, we
examined the correlation between the GIC and equatorial electrojet (EEJ) as
well as midlatitude H and D during the quasi-periodic DP2 fluctuations, SC,
Pi2 and so on.

To explain the flow of the ionospheric currents into the ground, we apply
the magnetosphere-ionosphere-ground transmission line model [Kikuchi,2014].

Quasi-periodic DP2 magnetic fluctuations at highlatitude and equator correlated with the IMF
Quasi-periodic DP2 magneticfluctuations are caused by convection
electric fields controlled by the IMF.
(Nishida, JGR 1968)

Quasi-periodic DP2 fluctuations caused by
IMF Bz fluctuations

Solar wind dynamicpressure
Interplanetary
magnetic field (IMF)

Equatorial electrojet(EEJ)(Kikuchi et al., JGR 2010)

am-H

DP2 currents at midequatorial latitudes(H/X-component)

pm-H

The am-H and pm-H components
are anti-correlated with each otherat mid latitudes.
EEJ is correlated with pm-H andanti-correlated with am-H.

EEJ

am: morning
pm: afternoon

am-D

DP2 currents at midequatorial latitudes(D/Y-component)

pm-D

The am-D and pm-D components
are anti-correlated with each otherat mid latitudes.
EEJ is correlated with am-D andanti-correlated with pm-D.

EEJ

GIC in the morning sector during the DP2 event

The am-GIC is correlatedwith EEJ.
Suggests that the GIC isconnected with the global
DP2 currents.

am-H

Another GIC event in themorning sector
The am-H and am-D components
are anti-correlated with each otherat mid latitudes.

am-D

EEJ is correlated with am-D andanti-correlated with am-H.

EEJ

GIC in the morning sector during the DP2 event

The am-GIC is correlatedwith EEJ.
Suggests that the GIC isconnected with the global
DP2 currents.

pm-H

GIC in the afternoon sector
during the DP2 event
The pm-H and pm-D components
are anti-correlated with each otherat mid latitudes.

pm-D

EEJ

EEJ is correlated with pm-H andanti-correlated with pm-D.

GIC in the afternoon sector during the DP2 event

The pm-GIC is anticorrelated with EEJ.
Suggests that the GIC isconnected with the global
DP2 currents.

am-H

GIC in the morning sector
during the SC event
The am-H and am-D components
are anti-correlated with each otherat mid latitudes.

am-DEEJ

EEJ is correlated with am-D andanti-correlated with am-H.

GIC in the morning sector during the SC event

The am-GIC is correlatedwith EEJ.
Suggests that the GIC isconnected with the global
SC currents.

GIC in the morning sector during the Pi2 event

The am-GIC is correlatedwith EEJ.
Suggests that the GIC isconnected with the global
Pi2 currents.

Induction or wave ?
×

∂B−
=E∂t
∂B−= ∇×E∂t

E 1Z=B µ0(Z: wave impedance)

Earth-ionosphere waveguide (transmission line)
model for the polar – equatorial current circuit(Kikuchi et al., 1978; Kikuchi and Araki, 1979)

ＴＭ0 mode waves carryelectric currents in theionosphere and on the ground,which are connected by thedisplacement currents on thewave front.

Magnetosphere-ionosphere-groundDP2 currents flow into theground from the(MIG) current circuit
magnetospheric dynamo(Kikuchi, JGR 2014)
down the magnetic field lines,
polar-equatorial ionosphere
Dynamo in the outerand wave front of the TM0
magnetospheremode waves in the EarthFAC-2
ionosphere waveguide.
FAC-1
Magnetic field line(-)(+)

H
Inner magnetosphere

Polar ionosphere
H

Induced currents on the ground

Earth

Pedersen currents

Low latitude
ionosphere
Wave front currents ofthe TM 0 mode waves

Magnetosphere-ionosphere-ground (MIG) transmission line
Transmission line parameters
d1 = 80 ,000 km (length of the FAC transmission line)(Kikuchi, JGR 2014)

d 2 = 8,000 km (length of the EIG transmission line)w = 2 ,000 km (width of the FAC and EIG transmission lines)l = 2 ,000 km (separation of the FAC transmission line)h = 100 km (separation of the EIG transmission line)
VA = 1, 000 km (Alfven speed)Σ1 =8 mho (height-integrated conductivity of the polar ionosphere)Σ 2 =0.2 - 30 mho (height-integrated ionospheric conductivity of the EIG)

Intrinsic impedanceZ 01 = µ0VA =1.26 ohm
Z=µ=376.7 ohm
020c

Characteristic impedance
Z1 = µ0VA =1.26 ohm
h=Z 2 376=.718.8 ohm
w

Reflection and transmission coefficients
CrR1Z 2 − Z1( R1 + Z 2 )= − 0.821
R1Z 2 + Z1( R1 + Z 2 )Ct =2 R1Z 2= 0.179
R1Z 2 + Z1( R1 + Z 2 )The transmitted electric and magnetic fields
excite the TM0 mode wave.

Transmission line equation
1  ∂ 2V
∂ 2V
∂V =+α ,22 2Vph  ∂t
∂x∂t 1  ∂2 I
∂2 I
∂I =+α  ,22 2Vph  ∂t∂x∂t where Vph 2 =1R(phase velocity) , α = (attenuation rate).
LCL

Ionospheric and ground surface currents
in the finite-length transmission line α I1 τ 2 − tn12  tα
 ∞  − α tn 1
− τα222∑ e U ( t − tn1 ) + tn1 ∫ e U ( t − τ )dτ 222 tn 1
 n =1 τ − tn1  
V2 ( x,t ) = V0 
α 
I1 
τ 2 − tn 2 2   tα∞  −α t− ταn22 dτ  − ∑  e 2 U ( t − tn 2 ) + tn 2 ∫ e 2 U ( t − τ ) 222
n =1 
τ − tn 2tn 2 

(5-11)

1 − α2 t  ∞α 2 ∞
α 2e ∑ U ( t − tn1 ) I 0 t − tn12  + ∑ U ( t − tn 2 ) I 0 t − tn 2 2  22Z2
 n1
 n 1=(5-12)=I 2 ( x ,t ) V0

tn12( n − 1 )d 2 + x
2nd 2 − xtn 2=cc(5-13)

The ionospheric currents are carried bymultiple TM0 mode waves propagating
along the finite-length transmission line.
The ionospheric currents are connectedwith the ground surface currents by thewave front currents of the multiple TM0mode waves.

Summary
The GIC has been suggested to be a return of the ionosphericcurrents [Watari et al., 2009; Braendlein et al., JGR 2012].
 In this paper, we have shown that the midlatitude GIC is wellcorrelated with the equatorial electrojet as well as the midlatitude
H- and D-components, suggesting that the GIC is closely
connected with the global ionospheric currents developing fromhigh latitude to the equator.
 The magnetosphere-ionosphere-ground transmission line model[Kikuchi, JGR 2014] helps understand the current flow from theionosphere to the ground, which are connected by the wave front
currents of the TM0 mode waves propagating in the Earthionosphere waveguide [transmission line].
