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

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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

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time

Bz > 0 　　　　 Bz < 0

Tailward flowsEarthward flows

Bz > 0 　　　　 Bz < 0

ion velocitydistribution functions

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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 site04/20/23 01:29 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 site04/20/23 01:29 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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Ve

Vi

Vi

Ve

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Ve

Vi

Vi

Ve

electron Vx

ion Vx

ion Vy

electron Vy

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

-62.5 km/stailward velocity of reconnection site04/20/23 01:29 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

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Structure of electron jets in magnetic reconnection

Locations of Magnetic Reconnection Events

MHD ion-electron decoupling

out-of-plane current

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Structure of electron jets in magnetic reconnection

Locations of Magnetic Reconnection EventsBz turning

MHD

observation simulation at TΩi = 35

Vix / Vex 0.2-0.3 0.1

Vey / Vex 1.25 1.4

Vix 0.5 VA 0.3 VA

the full extent of the central 1 i 1 ielectron current layer

the full extent of 8 i 8 ithe ion-electron decouplingregion

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30 Magnetic Reconnection EventsIn 1996-2012

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Main Targets of This Paper

1.Detect the central intense electron current layer2.Get scales of magnetic reconnection

with Geotail observations

VA = 2,200 km/s i = 1,200 km (ion inertial length)

Geotail MGF 16 vectors /sLEP 12 s

electron g-factor 4x10 T 5.5x10

-4

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The simulation box size [−Lx/2,+Lx/2]×[−Lz/2,+Lz/2] Lx = 48D Lz = 24D

initial current sheet thickness D = 0.5λiΔ is equal to the Debye λi = 200Δ

The number of simulation grids 4800×2400

Particle number 1.5×10 particles for each species nCS Ti;CS/Te;CS = 5nBK = nCS Ti;BK = Te;BK = Te;CS

ion to electron mass ratio mi/me = 400

frequency ratio ωpe/Ωe = 4,ωpe ≡√4πnCSe2/me Ωe ≡ eB0/mec λi ≡ c/ωpi = c/√4πnCSe2/mi

The initial magnetic field the Harris sheet Bx(z) = B0 tanh(z/D) B0 the asymptotic magnetic field

D the current sheet half-thicknessThe perturbed magnetic flux function ψ(x, z) = ψ0 sin(2πx/Lx) cos(2πz/Lz)

B (x, z) = eˆy × ψ∇ (x, z)

at TΩi = 35 Vi x ∼ 0.3VA VA the Alfven speed B0/√4πminCS

9

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time

Bz > 0 　　　　 Bz < 0

Tailward flowsEarthward flows

Bz > 0 　　　　 Bz < 0

Vy < 0 dawnward

Vy > 0 duskward

electron velocitydistribution function

In the equatorial plane

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Earth tail

time

Bz > 0 　　　　 Bz < 0

Tailward flowsEarthward flows

Bz > 0 　　　　 Bz < 0

Hall electrons

electron velocitydistribution function

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Earth tail

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electron Vxion Vx

electron Vyion Vy

MHD flows

Vi = Ve

Errors are smallwhen energetic electrons are rich.