January 19, 2011

Construction of Magnetic Reconnection in the near-Earth Magnetotail with Geotail

T. Nagai Tokyo Institute of TechnologyI. Shinohara ISAS/JAXA

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MHD Picture of Magnetic Reconnection

inflow

outflowBz > 0 Bz < 0

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Ion flows

Electron flows

unit ViA

unit VeA

Particle Picture of Magnetic Reconnection

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Hall Magnetic Fields

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Ve Ve

Vi Vi

Outflows

Bz > 0 　　　　 Bz < 0

MHD Ion-electron decoupling MHD

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- Vey

electron current layer

Bz > 0 　　　　 Bz < 0

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15 May 2003

near 1055 UT

the spacecraftGeotail at 28 RE

in situ observations ofmagnetic reconnection

Geotail

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Tailward flows

Earthward flows

Bz < 0 Bz > 0

Tailward flows

Earthward flows

Ion Et

Bz > 0 　　　　 Bz < 0

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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

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Tailward flows

Earthward flows

Bz < 0 Bz > 0

Tailward flows

Earthward flows

Ion Et

5 minutesBz > 0 　　　　 Bz < 0

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Bz < 0 Bz > 0

Tailward flows

Earthward flows1000 km/s ion flow

VA = 2200 km/s

Bz > 0 　　　　 Bz < 0

11

Ion observations

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Bz < 0 Bz > 0

Vx > 3000 km/s electron flows

Vy > 6000 km/s electron flows

Ve

Vi

Ve

Bz > 0 　　　　 Bz < 0

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Ion flows vs. electron flows

Ion Et

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Vx > 2000 km/s electron flows

Vy > 3000 km/s electron flows

VBz < 0 Bz > 0

Ve

Ve

Bz > 0 　　　　 Bz < 0

Tailward flows

Earthward flows

13

Ion and electron flows

perpendicular to the magnetic field

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Vx > 2000 km/s electron flows

Vy > 3000 km/s electron flows

VBz < 0 Bz > 0

Ve

Ve

Bz > 0 　　　　 Bz < 0

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Electron observations

acceleration and heating

electron Et

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time

Bz > 0 　　　　 Bz < 0

Tailward flowsEarthward flows

Bz > 0 　　　　 Bz < 0

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15

> 8.47 keV electron directional fluxes

Earth tail

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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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16

Earth tail

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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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time

Bz > 0 　　　　 Bz < 0

Tailward flowsEarthward flows

Bz > 0 　　　　 Bz < 0

ion velocitydistribution functions

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Earth tail

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time

Bz > 0 　　　　 Bz < 0

Tailward flowsEarthward flows

Bz > 0 　　　　 Bz < 0

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1057:44 1053:44 UT

time

Bz > 0 　　　　 Bz < 0

Tailward flowsEarthward flows

Bz > 0 　　　　 Bz < 0

counter-streaming inflows

ion velocitydistribution functions

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1057:44 1053:44 UT

ion-electron decoupling Ve >> Vi

intense electron current layer

large Vey

spatial scales?

Important Questions

MHD MHD

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+450 km/s -650 km/s

Earthward flow speed tailward flow speed

MHD flows

22

Asymmetric outflows

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

MHD flows

tailward velocity of reconnection site 2319:47

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

inflows

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Asymmetric inflows

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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 site 2519:47

ion-electron decoupling region

8 i

central electron current layer

1 iMHD MHD

Vx peakFlux peak

Ion ele ele ion

Earth tail

8 i = 1.5 RE 1 i = 1200 km 2619:47

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

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28

PIC simulation results

the northern earthward sideof the reconnection site(upper-left quadrant)

the X-line position

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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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Geotail Survey ofTailward Flows with Bz < 0 in 1995-2003

209 events

Nagai et al., 2005 30

8 i = 1.5 RE ion-electron decoupling region

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Geotail Reconnection Events= Observations of Ion-Electron Decoupling Region

34 events 34/208 = 0.16

reconnection events at 20-30 RE

Nagai et al., 1998; 20013119:47

Most of Events are MHD FlowsReconnection Events 34 events

34/208 = 0.16

reconnection events at 20-30 RE 10 RE x 0.16 = 1.6 RE

3219:478 i = 1.5 RE ion-electron decoupling region

ion-electron decoupling region

8 i

central electron current layer

1 iMHD MHD

Vx peakFlux peak

Ion ele ele ion

Earth tail

8 i = 1.5 Re 1 i = 1200 km 3319:47

Main conclusions

In the magnetic reconnection site of the near-Earth magnetotail

1.the central intense electron current layer 1 i2.ion-electron decoupling region 8 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, 2010JA016283, 2011.

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