Chapman Conference“Fundamental Properties and Processes of Magnetotails” 12 March 2013, Tuesday, 1205-1220 p.m.

Structure of Magnetic Reconnection in the Earth’s Magnetotail

Geotail Observations

T. Nagai Tokyo Institute of Technology

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20th Anniversary of Geotail Observations

Launch on 24 July 1992

Prof. Atsuhiro Nishida

“Person of Cultural Merit” in 2012(an official Japanese recognition and honor)

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20-year Geotail observations

2 clear-cut encounters of the magnetic reconnection site

observation observation time probability

ion-electron decoupling region 336 s 0.000,000,53

(96+240)

electron diffusion region 36 s 0.000,000,057 (12+24)

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Magnetic field structure

Outflows (electron Vx and ion Vx)

Out-of-plane current(electron Vy and ion Vy)

Magnetic Reconnection Simulation

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1055 UT

15 May 2003

Tailward flows

Earthward flows

Bz < 0 Bz > 0

Tailward flows

Earthward flows

ion energy-time diagrams

5 minutesBz > 0 　　　　 Bz < 0

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Ve

Ve

Ve

Ve

Vi

Vi

Vi

Vi

Magnetic field(MGF)

Plasma (LEP)

Ion and electron

Velocity

Number density

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electron Vx

ion Vx

ion Vy

electron Vy

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electron Vx

ion Vx

ion Vy

electron Vy

electron E-t

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-vix+vix

+vex-vex

Direct detection of the dissipation region

S. Zenitani, I. Shinohara, and T. Nagai, Geophys. Res. Lett., 39, L11102, 2012.

ion-electron decoupling Ve >> Vi

intense electron current layer

large Vey

Spatial Scales

MHD MHD

1057:44 1053:44 UT

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time

Bz > 0 　　　　 Bz < 0

Tailward flowsEarthward flows

Bz > 0 　　　　 Bz < 0

ion velocitydistribution functions

1057:44 1053:44 UT

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Earth tail

+450 km/s -650 km/s

Earthward flow speed tailward flow speed

MHD flows

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Asymmetric MHD outflows

+550 km/s -550 km/s(+450 km/s) (-650 km/s) -100 km/s

MHD flows

tailward velocity of reconnection site04/22/23 04:26 14

time

Bz > 0 　　　　 Bz < 0

Tailward flowsEarthward flows

Bz > 0 　　　　 Bz < 0

counter-streaming inflows

ion velocitydistribution functions

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Vx = +64 km/s Vx= -269 km/s

inflows

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Asymmetric inflows

Vx = +164 km/s Vx= -169 km/s (+264 km/s -269 km/s)

-100 km/s

inflows

Cluster results

-100 km/s Baker et al. 2002Imada et al. 2007

tailward velocity of reconnection site04/22/23 04:26 17

Earth Tail

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1 i8 i

8 i = 1.5 RE 1 i = 1200 km

Geotail 15 May 2003

VMR = -100 km/s

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0700 UT

05 May 2007

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Ve

Ve

Ve

Ve

Vi

Vi

Vi

Vi

Magnetic field(MGF)

Plasma (LEP)

Ion and electron

Velocity

Number density

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electron Vx

ion Vx

ion Vy

electron Vy

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Ve

Vi

Vi

Ve

electron Vx

ion Vx

ion Vy

electron Vy

electron E-t

Vx = +437.5 km/s Vx= -437.5 km/s (+375 km/s -500 km/s)

-62.5 km/stailward velocity of reconnection site04/22/23 04:26 23

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8 i = 1.5 RE 1 i = 1200 kmVMR = -62.5 km/s

1 i13 i

Main conclusions

In the magnetic reconnection site of the near-Earth magnetotail

1.the central intense electron current layer (10 nA/m ) 1 i2.ion-electron decoupling region 10 i3.MHD regions outside the i-e decoupling region

Nagai, T., I. Shinohara, M. Fujimoto, A. Matsuoka, T. Saito, and T. Mukai, J. Geophys. Res., 116, A04222, 2011.

Zenitani, S., I. Shinohara, and T. Nagai,Geophys. Res. Lett., 39, L11102, 2012.

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2

1 i

10 i

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3D structure of magnetic reconnection

Locations of MagneticReconnection Events

8 REdawn-dusk width

10 i