Three Species Collisionless Reconnection: Effect of O + on Magnetotail Reconnection
Magnetotail Current Sheet IKI26-30 September 2011 Magnetic Reconnection in the Current Sheet:
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Transcript of Magnetotail Current Sheet IKI26-30 September 2011 Magnetic Reconnection in the Current Sheet:
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Magnetotail Current Sheet IKI 26-30 September 2011
Magnetic Reconnection in the Current Sheet: Geotail Observations
Wednesday 28 September 2011, 1220-1300
T. Nagai Tokyo Institute of Technology
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The basic physical components on the magnetic reconnection site
1.The central electron current layer – the (electron) diffusion region
2.The ion-electron decoupling region – the Hall physics region
3.Inflows and Outflows – the MHD region
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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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The basic physical components on the magnetic reconnection site
1.The central electron current layer – the (electron) diffusion region
2.The ion-electron decoupling region – the Hall physics region
3.Inflows and Outflows – the MHD region
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0700 UT
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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 Vperp x
electron Vperp y
10 nA/m2
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0630 UT
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electron Vx
electron Vy
ion Vx
ion Vy
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electron Vx
electron Vy
electron Vperp x
electron Vperp y
20 nA/m2
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1055 UT
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electron Vx
ion Vx
ion Vy
electron Vy
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Geotail Observationsin the Plasma Sheet(plasma > 1)
in 1994-2010 X = -18 to -30 RE
Y = -20 to +20 RE
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electron Vxion Vx
electron Vyion Vy
MHD flows
Vi = Ve
Errors are smallwhen energetic electrons are rich.
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Tailward Flows with Bz < 0
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Tailward flows with Bz < 0
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Reconnection events
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Physical Size ofthe Magnetic Reconnection Site
in the X direction
in the Y direction
?
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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
-4
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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
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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
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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
1057:44 1053:44 UT
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> 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
1057:44 1053:44 UT
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Earth tail
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time
Bz > 0 Bz < 0
Tailward flowsEarthward flows
Bz > 0 Bz < 0
Hall electrons
electron velocitydistribution function
1057:44 1053:44 UT
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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
1057:44 1053:44 UT
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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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time
Bz > 0 Bz < 0
Tailward flowsEarthward flows
Bz > 0 Bz < 0
counter-streaming inflows
ion velocitydistribution functions
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ion-electron decoupling Ve >> Vi
intense electron current layer
large Vey
spatial scales?
Important Questions
MHD MHD
1057:44 1053:44 UT
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+450 km/s -650 km/s
Earthward flow speed tailward flow speed
MHD flows
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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 site04/22/23 01:21 42
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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
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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
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ion-electron decoupling region
8 i
central electron current layer
1 iMHD MHD
Vx peakFlux peak
Ion ele ele ion
Earth tail
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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., 200504/22/23 01:21 49
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; 200104/22/23 01:21 50
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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
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ion-electron decoupling region
8 i
central electron current layer
1 iMHD MHD
Vx peakFlux peak
Ion ele ele ion
Earth tail
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Geotail Observationsin the Plasma Sheet(plasma > 1)
in 1994-2010 X = -18 to -30 RE
Y = -20 to +20 RE
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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, A04222, 2010JA016283, 2011.
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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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1. What are the major latest achievements in the topic of the section?
2. What major results are still expected/possible given the available data (ongoing projects) ?
3. What are major questions to be answered by future missions?
Some comments:
Location of magnetic reconnection
A mechanism (or mechanisms) of the current sheet thinning
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Location of Magnetic Reconnection
Aurora Onset Location
Morning
Midnight
Evening
X = -20 to -30 RE and Y = -5 to +10 RE
Invariant Latitude degrees MLT
Grocott et al. 2009
High Occurrence
Nagai et al., 1998a
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Magnetic reconnection at a substorm onset
Fast Tailward Flows
Bz < 0
Fast tailward Flowswith Bz < 0
Fast Earthward Flowswith Bz > 0
Ieda et al. 2008
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Evidence of Magnetic Reconnection
1. Acceleration of electrons2. Hall current system
Ions
Electrons
Accelerated electrons
1530 1540 UT February 18, 1996
High speed ion flows & Bz <0
Nagai et al., 2001
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Geotail observations at 25 RE
1996/02/18
strong acceleration of electrons
strong acceleration of electrons
thermal
accelerated
electron energy spectra
Flux
Energy
1530 1540 UT
> 2000 km/s tailward flowing ions
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Geotail observations at 25 RE
1996/02/18
strong acceleration of electrons
1530 1540 UT
> 2000 km/s tailward flowing ions
48 sec
Time scale ofclosed field line reconnection open field lines reconnection
12 sec
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X-line tailward motion
Tailward motion of reconnection site
Hones et al., 1973
Substorm models
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current continuity
current continuity?
Structure of the cross-tail current system
intense electron current layer
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Location of Magnetic Reconnection
Aurora Onset Location
Morning
Midnight
Evening
X = -20 to -30 RE and Y = -5 to +10 RE
Invariant Latitude degrees MLT
Grocott et al. 2009
High Occurrence
Nagai et al., 1998a
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An initial onset in the pre-midnight sector
East-wst expansion of the onset region
at Geosynchronous orbit (6.6 Re)
Nagai JGR 1982
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NagaiJGR 1987
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Nagai JGR 1987
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Location of Magnetic Reconnection
Aurora Onset Location
Morning
Midnight
Evening
X = -20 to -30 RE and Y = -5 to +10 RE
Invariant Latitude degrees MLT
Grocott et al. 2009
High Occurrence
Nagai et al., 1998a
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IMF Bz prior to magnetic reconnection onset
The site of magnetic reconnection
Near-Earth X = -15 to -25
Middle X = -25 to -31
Typical growth phase 4 minnorthward turning(IMF-triggered 60%)
Nagai et al., 2005Hsu and McPherron, 2003
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Nagai et al., 2005
threshold
Solar wind electric field
E = V x Bs Flux accumulation
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Near-Tail
Midtail
The solar wind energy input controls the magnetic reconnection site.
Solar wind Electric field
E = V x Bs
Nagai et al., 2005
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Position of magnetic reconnection tailward edge of thin current sheet
thin current sheet
substorm onset
Asano et al., JGR 2004
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IMF Bz southward turning
More taillike configuration(the growth phase)
The thinning
Geotail observations in the plasma sheetIn the growth phase
Nagai GRL 1997
No drastic changes
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plasma sheet structureprior to an onset
Near the equatorial plane Bx = 0
Increase of number density
Decrease of temperature
Increase of total pressure
Bx
By
Bz
Bt
Vx
ion
electron
density
Ti
Pt Pp
magnetic reconnection
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A mechanism (or mechanisms) of the current sheet thinning
Miho Saito, D. Fairfield, G. Le, L.-N. Hau, V. Angelopoulos, J. McFadden, H.-U. Auster, J. Bonnell, and D. Larson (2011),
Structure, force balance, and evolution of incompressible cross-tail current sheet thinning,
J. Geophys. Res., doi:10.1029/2011JA016654, in press.
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P5 THA
P2 THC
P3 THD
P4 THE
IMF Bz southward turning
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Z=0.20Z=0.15Z=0.10Z=0.05Z=0.00
X=0.0X=0.4X=0.8X=1.2
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[−Lx/2,+Lx/2]×[−Lz/2,+Lz/2] Lx = 48D Lz = 24D D = 0.5λi λi = 200Δ Debye length simulation grids is 4800×2400 1.5×109 particles
mi/me = 400 ωpe/Ωe = 4
Ti;CS/Te;CS = 5
Initial Current Thickness 0.5 i (Harris Current Sheet) Bx(z) = B0 tanh(z/D)
Results at time i t = 35 Vi x 0.3VA ∼
2D Full Particle Simulations
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Typical Plasma Parameters
Alfven velocity 2200 km/sBlobe = 20 nTDensity = 0.04 cm-3(plasma sheet)
ion inertial length 1200 km Density = 0.04 cm-3
i = V / i = c / pi
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The initial magnetic field the Harris sheet Bx(z) = B0 tanh(z/D) B0 the asymptotic magnetic field
D the current sheet half-thickness
nCS the current sheet has number densityTi;CS/Te;CS = 5 ion to electron temperature ratio
nBK = nCS a uniform background plasmaTi;BK = Te;BK = Te;CS
The perturbed magnetic flux function ψ(x, z) = ψ0 sin(2πx/Lx) cos(2πz/Lz)B (x, z) = eˆy × ψ∇ (x, z)
nCS the current sheet has number densityTi;CS/Te;CS = 5 ion to electron temperature ratio
nBK = nCS a uniform background plasmaTi;BK = Te;BK = Te;CS
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The simulation box size is [−Lx/2,+Lx/2]×[−Lz/2,+Lz/2] Lx = 48D and Lz = 24D
Periodic boundary conditions are imposed in the x directionconducting walls are set at the z boundaries
ion to electron mass ratio mi/me = 400
frequency ratio ωpe/Ωe = 4,initial current sheet thickness D = 0.5λiωpe ≡√4πnCSe2/me, Ωe ≡ eB0/mec, and λi ≡ c/ωpi = c/√4πnCSe2/mi
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The spatial grid size Δ is equal to the Debye length of the background plasma, and λi = 200Δ
The number of simulation grids is 4800×2400
1.5×109 particles for each species
Vi x ∼ 0.3VA at TΩi = 35
VA the Alfven speed is defined by B0/√4πminCS
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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
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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