chapman conference “fundamental properties and processes of magnetotails”
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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. NagaiTokyo Institute of Technology. Launch on 24 July 1992. - PowerPoint PPT PresentationTRANSCRIPT
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.