Magnetotail reconnection and flux circulation: Jupiter and Saturn compared
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:
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
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
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
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
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
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
time
Bz > 0 Bz < 0
Tailward flowsEarthward flows
Bz > 0 Bz < 0
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> 8.47 keV electron directional fluxes
Earth tail
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
time
Bz > 0 Bz < 0
Tailward flowsEarthward flows
Bz > 0 Bz < 0
ion velocitydistribution functions
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Earth tail
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
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+450 km/s -650 km/s
Earthward flow speed tailward flow speed
MHD flows
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Asymmetric outflows
+550 km/s -550 km/s(+450 km/s) (-650 km/s) -100 km/s
MHD flows
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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
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
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
Geotail Reconnection Events= Observations of Ion-Electron Decoupling Region
34 events 34/208 = 0.16
reconnection events at 20-30 RE
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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
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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
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
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
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
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
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
X-line tailward motion
Tailward motion of reconnection site
Hones et al., 1973
Substorm models
current continuity
current continuity?
Structure of the cross-tail current system
intense electron current layer
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
An initial onset in the pre-midnight sector
East-wst expansion of the onset region
at Geosynchronous orbit (6.6 Re)
Nagai JGR 1982
NagaiJGR 1987
Nagai JGR 1987
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
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
Nagai et al., 2005
threshold
Solar wind electric field
E = V x Bs Flux accumulation
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
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
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
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