磁気圏における magnetic reconnection
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磁気圏における Magnetic Reconnection. ー MHD 的描像から粒子的描像へ -. 長井嗣信 東京工業大学. 地球磁気圏での magnetic reconnection. 昼側での磁気リコネクション. 夜側での磁気リコネクション. Dungey model (J. W. Dungey, Phys. Rev. Lett., 6, 47, 1961). Geotail Observations Sun. Solar Wind. Bow Shock. Magetosheath. Magnetopause. Magnetotail. - PowerPoint PPT PresentationTRANSCRIPT
磁気圏におけるMagnetic Reconnection
長井嗣信東京工業大学
ー MHD 的描像から粒子的描像へ -
地球磁気圏での magnetic reconnection
Dungey model (J. W. Dungey, Phys. Rev. Lett., 6, 47, 1961)
昼側での磁気リコネクション
夜側での磁気リコネクション
Geotail Observations
Sun
Solar Wind
Magetosheath
Magnetotail
Bow Shock
Magnetopause
磁気圏尾部での磁気リコネクションの証拠 Geotail 以前 サブストーム(オーロラ爆発) ( 1960 年代より)
Fast Tailward Flows
Bz < 0
Fast tailward Flowswith Bz < 0
Fast Earthward Flowswith Bz > 0
地球半径の 30倍の距離での磁気圏尾部での磁場とプラズマの観測
磁気圏尾部の磁場はダイポール磁場が引き伸ばされたものだからすべて北向き
Kadokura (2002)SIT-TV at Syowa427.8 nm
オーロラ爆発の全天カメラ像a substorm onset (aurora breakup)
人工衛星 Geotail による観測 (1992-)
研究テーマ
MHD 的磁気リコネクションの確立
Spacecraft GeotailLaunch July 22, 1992
Orbit 30 RE x 10 RE
period 5 days
Magnetic field 1/16 sec 0.01 nT
Plasma 12 sec ion and electron 0 – 40 keV 3D velocity distribution functions MHD parameters (n, T, V)
Geotail
プラズマの 3 次元速度分布関数の観測
Ion Electron
High-Speed Tailward Flowing Ions
High ly Accelerated Electrons
V=3000km/s
Heated Inflow IonsHigh V
Outflow Ions
Outflow IonsConvection
磁気リコネクションの観測例
EQ
off EQ
boundary
Bz < 0
XGSM=-28.9 YGSM=5.8 ZGSM=-2.6 RE Less HeatedInflow IonsLow V
Outflow Ions
Vx < 0
磁気圏尾部での磁気リコネクションの観測例
南向き磁場を持つ反地球向き高速プラズマ流電子の加熱・加速
X
Z
Bx > 0 北半球Bx < 0 南半球
Bx =0 赤道面 (電流層)
太陽の方向
Magnetic Field Direction B
Distribution Functions
V Convection
B B
V V
Stationary Field-aligned flows Convection flows
プラズマ速度分布関数の MHD 的描像 B – V 座標系
磁力線に沿う流れ field-aligned flows
磁力線に垂直な流れ convection flows (frozen-in)
Ion Electron
High-Speed Tailward Flowing Ions
High ly Accelerated Electrons
V=3000km/s
Heated Inflow IonsHigh V
Outflow Ions
Outflow IonsConvection
Boundary
off EQ
EQ
Less HeatedInflow IonsLow V
Outflow Ions
C
B
A
A near the equatorial plane
Ion Electron
High-Speed Tailward Flowing Ions
High ly Accelerated Electrons
Outflow IonsConvection
Magnetotail Reconnection Event
EQ
Magnetic Field Direction B
V Convection
A near the equatorial plane
High-Speed Tailward Flowing Ions
High ly Accelerated Electrons
Outflow IonsConvection
Magnetotail Reconnection Event
EQ
Ion Electron
Tailward convection flows with Bz < 0 Vi > 2500 km/s
Alfven velocity ~2900 km/s
B off the equatorial plane
Ion Electron
High-Speed Tailward Flowing Ions
High ly Accelerated Electrons
Magnetotail Reconnection Event
Magnetic Field Direction B
V Convection
B off the equatorial plane
Ion Electron
High-Speed Tailward Flowing Ions
High ly Accelerated Electrons
Magnetotail Reconnection Event
Tailward field-aligned Flows with Bz < 0 V > 2800 km/s
MHD magnetic reconnection simulation (T. Sato, 1979)
Ion Electron
High-Speed Tailward Flowing Ions
High ly Accelerated Electrons
V=3000km/s
Heated Inflow IonsHigh V
Outflow Ions
Outflow IonsConvection
磁気リコネクションの観測例
Boundary
off EQ
EQ
Less HeatedInflow IonsLow V
Outflow Ions
C
B
A
Magnetic Field Direction B
Distribution Functions
V Convection
B B
V V
Stationary Field-aligned flows + Convection flows
V
B
Convection flowswith counter-streaming components
V
V//
V//
High-Speed Tailward Flowing Ions
High ly Accelerated Electrons
V=2500km/s
Outflow IonsConvection
Magnetotail Reconnection Event
EQ
Ion Electron
Tailward convection flows with Bz < 0 Vi > 2500 km/s Ve > 4000 km/s ion-electron decoupling Alfven velocity ~2900 km/s
A near the equatorial plane
High-Speed Tailward Flowing Ions
High ly Accelerated Electrons
V=3000km/s
Heated Inflow IonsHigh V
Outflow Ions
Magnetotail Reconnection Event
off EQB
Ion Electron
B off the equatorial plane
Ion Electron
High-Speed Tailward Flowing Ions
High ly Accelerated Electrons
V=3000km/s
Magnetotail Reconnection Event
Boundary
Less HeatedInflow IonsLow V
Outflow Ions
C
C boundary
Ion Electron
High-Speed Tailward Flowing Ions
High ly Accelerated Electrons
V=3000km/s
Magnetotail Reconnection Event
Boundary
Less HeatedInflow IonsLow V
Outflow Ions
C
Tailward Escaping Electrons
Inflowing Electrons
Hall Current Electrons
C boundary
人工衛星 Geotail による観測 (1992-)
研究テーマ
MHD 的描像の磁気リコネクションの確立
粒子的描像の磁気リコネクションの世界への発展
Classical MHD steady magnetic reconnection
Sweet-Parker reconnection Petscheck reconnection
reconnection rate
イオンと電子の運動を考慮した磁気リコネクションモデル
粒子的描像
Geospace Environmental Modeling (GEM) Magnetic Reconnection Challenge (Birn et al. J. Geophys. Res., 2001)
B. U. O. Sonnerup (1979)
Ion-Electron Decoupling
イオンー電子の二流体による磁気リコネクションモデル
イオン慣性長程度でのスケールでの物理
Ion NOT frozen-in
Electron still frozen-in
Ion-Electron Decoupling (non-MHD)
Hall Effect
electron-ion+
electron
ion+
-
Magnetic field
electron diffusion region e
ion diffusion region i ~ 40 e
Ion-Electron Decoupling at the i Scale
electron-ion+
electron
ion+
-
Magnetic field
electron diffusion region e
ion diffusion region i ~ 40 e
j ホール電流
ホール電流系の形成
electron-ion+
electron
ion+
-
Magnetic field
electron diffusion region e
ion diffusion region i ~ 40 e
j ホール電流
ホール磁場 By < 0
ホール磁場の形成 4重極構造
electron-ion+
electron
ion+
-
Magnetic field
electron diffusion region e
ion diffusion region i ~ 40 e
ホール電場の形成
E
ExB で紙面向こうむきのドリフト (dawnward motion)
一般化したオームの法則で MHD で無視した項の役割
電子慣性項 電子圧力項 ホール項 異常抵抗項
eii
非対角成分
1/2
e = c / pe 5.3/ n (/cc) km
i = c / pi 227/ n (/cc) km
V. M. Vasyliunas, Rev. Geophys. Space Phys. 1975
1/2
1/2
Energy = 1 keV B = 10 nT
Velocity Larmor Radius Period
Proton 440 km/s 460 km 6.6 sec
Electron 18800 km/s 11 km 0.004 sec
Proton 4600 sqrt(E) / B km 66 / B sec
Electron 110 sqrt(E) / B km 0.036 / B sec
地球磁気圏尾部での典型的物理量
1 RE = 6371.2 km 地球半径
磁気圏尾部 幅 40 RE 厚さ 10 RE
磁場 20 nT 密度 0.3 /cc 温度 3 keV イオン
磁気リコネクション領域での物理量
プラズマの厚さ 1 イオン慣性長
外部の磁場とプラズマ 20 n T 0.01 /cc Alfvén 速度 4000 km/s
ion inertial length 500 km i = V / i = c / pi
me/mi 1/100
Particles 33,554,432 (Av. 128 /grid)
Grid Size 512 x 512
Ion Inertial Length 32 gridsElectron Inertial Length 3.2 grids
Initial Current Thickness 0.5 i (Harris Current Sheet)Double-Periodic Boundary Conditions
Results at time i t = 18.0
2D Full Particle Simulations I. Shinohara
イオンの運動
電子の運動
イオンのアルフベン速度
電子のアルフベン速度
磁場の分布南北方向 Bz
イオンの速度
電子の速度
High-Speed Tailward Flowing Ions
High ly Accelerated Electrons
V=2500km/s
Outflow IonsConvection
Magnetotail Reconnection Event
EQ
Ion Electron
Tailward convection flows with Bz < 0 Vi > 2500 km/s Ve > 4000 km/s ion-electron decoupling Alfven velocity ~2900 km/s
磁場の分布南北方向 Bz
イオンの速度
電子の速度
Intense Bz
MHD weak Bz in the outflow region
the 3-min interval the 90-s interval
Bz = -36 nT
Bt = 36 nTtail lobeBt = 24 nT
10 sec
strong acceleration of electrons
strong acceleration of electrons
thermalaccelerated
electron energy spectra
Flux
Energy
The Hall current systemCurrents and By
Ion Electron
High-Speed Tailward Flowing Ions
High ly Accelerated Electrons
V=3000km/s
Magnetotail Reconnection Event
Boundary
Less HeatedInflow IonsLow V
Outflow Ions
C
Tailward Escaping Electrons
Inflowing Electrons
Hall Current Electrons
December 10, 1996
High-Speed Ion Flows
Highly Accelerated Electrons
Reconnection Event
Earthward Flows
Tailward Flows
Hall Current System
Earthward Tailward
Northern hemisphere
Southern hemisphere
Hall Current density ・・・・ 6 ~ 13 nA /m2
The Hall current loops exist with the double-current structure in the narrow regions near the separatrix layers.
By is created by the Hall current loop
By = 0.3 Bt lobe
M.S. Nakamura et al.(1998)
Hybrid simulationfor reconnection
Vex電子流体として外向きの流れ
Hoshino (1998)Particle simulation for reconnection
外向きの電子流と内向きの電子流の共存
Ion Electron
High-Speed Tailward Flowing Ions
High ly Accelerated Electrons
V=3000km/s
Magnetotail Reconnection Event
Boundary
Less HeatedInflow IonsLow V
Outflow Ions
CDawnward ion drift
Dawnward ion drift ExB drift Hall Electric Field
イオン 紙面向こう方向に流れながら赤道面方向へ
Geotail による観測により解明された磁気リコネクションの構造
MHD的描像 粒子的描像イオンの流入の加速 イオンと電子の分離した運動電子の流入と加速・加熱 ホール電流系とそれによる磁場を運ぶ Alfvenic Flows 4重極構造のホール磁場
ホール電場
Cluster Observations Henderson et al., GRL 2006
EH the Hall electric field
JxB/en
Cluster Observations Henderson et al., GRL 2006
Edivp the electric field by div Pe
-div Pe /en
EH >> Edivp
EH
Edivp
Hall current
Geotail 1996/01/27 Va 2900 km/s n 0.02/cc B 19 nT Vi -2500 km/s Ve -4000 km/s
j 7.5 nA/m**2
Geotail 6-13 nA/m**2 Eh 10 mV/m
Cluster 2003/08/24 Jx 20 nA/m**2 Bz 2.7 nT
E hall 4.22 mV/m Vdrift 500 km/s
Henderson Ez hall 6 mV/m Ez Pe 1 mV/m
電子圧力の非対角成分による電場
i scale
Geotail で解明された物理過程 ion dynamics
Geotail では解明できない物理過程 electron dynamics
磁気リコネクション electron diffusion region で起きる
1.何が dissipation を担うか 電子圧力の非対角成分 電子慣性 ホール項の役割 electron-positron plasmas
2. trigger mechanismresistive tearing modecollisionless electron tearing mode
ion tearing mode3. reconnection rate は何により決まるか4. scale of electron diffusion region
short vs. elongated
Trigger Mechanism Tearing Mode
A one-dimensional currant sheet a Harris current sheet model
ideal MHD stable (frozen-in constraint)
resistive MHD resistive tearing mode collisional(Furth, Killeen, and Rosenbluth, 1963)
kinetic electron tearing mode (electron Landau resonance)(Coppi et al., 1966)
ion tearing mode (ion Landau resonance)(Schindler, 1974)
temperature anisotropy Tperp/ Tpara
Difficulty
A magnetotail field configuration a normal magnetic field BnLembege and Pellat (1982), Pellat et al. (1991), Quest et al. (1996)Bn a strong stabilizing effect for electron tearing
Electron stabilization Galeev and Zelenyi (1976), Lembege and Pellat (1982)a stabilization effect for ion tearingelectron pitch angle scattering due to magnetic turbulences
Nonlinear ion tearing-like modeGaleev et al. (1978)electron effect is uncertain
Cross-scale coupling
Diffusion region electron scale
Acceleration processes ion scale
Boundary conditions MHD scaleMagnetospheric Phenomena
elongated electron diffusion region? 5 e 5-20 i super-Alfvenic agyrotropic electron jet
Secondary island quenching reconnection process2D world 3D world new instabilities?
Cluster 2003 tail observation Cluster separation 200-250 km Separation can be ≤ c/wpi
Curlometer technique ideal to estimate the current density profile. Structure within a thin current sheet can be resolved.
This talk
Thin current sheet crossings (>50 nA/m2) 2003/08/24 1820-1920, 2003/10/01 1940-2040
Discuss: Spatial/temporal changes in the current sheet structure
69
Cluster at postmidnight: X=-17,Y=-4,Z=-3 RE
Slow CS traversal and current density enhancement before onset
Multiple neutral sheet crossings during fast flow intervals
Substorm current sheet with fast flow
Pi2 onset
tailward flow
earthward flow
growth phase
20030824
72
Current sheet crossings
Check whether dBx/dz profile is the same for the two pairs of the observation stability of the CS during a crossing
(Coordinates determined from MVA)
73
Current sheet profile near X-line
Curlometer resolved current profile near reconnection region1903:28-1903:391843:17-1843:25
Reconnection observationReconnection observation
Ion and electron decoupling Hall electric current
JVionVelec.
electron demagnetized (electron diffusion)
ion demagnetized (ion diffusion)
Cluster fast (<4 fci-1) current sheet crossing likely
observed Hall current system in a current sheet with (full) thickness of ~ c/wpi in regions of tailward and
Earthward of X-line(s)
Cluster Reconnection Event on August 24, 2003
Bz
Vx
Ions
ElectronsNakamura et al. 2006
(-16.8, -3.8, 3.3 Re)
Hall Current System
Earthward Tailward
Northern hemisphere
Southern hemisphere
Nagai et al. (JGR 2001)
Cluster ObservationsAsano et al. 2006
The Hall current loops exist with the double-current structure in the narrow regions near the separatrix layers.
Geotail Observations
Nagai et al. JGR 2003
磁気中性線付近での荷電粒子の運動
S. W. H Cowley 1985
異常抵抗を作るものAnomalous Resistivity
波動
Lower Hybrid Waves ?
Shinohara et al. (1998)
SCOPE
In planning phase at ISAS/JAXALaunch ~2017
High-time resolutionElectron measurements
The daughter s/cdedicated to wave-particleInteraction issue
Ion scale dynamics monitors
Electron scale
Ion scale
SCOPE ele.-scale kernel~100km
Ion-scale shell~1000km
MHD-scale monitors
ESA-ISAS “CrossScale”
太陽フレアーの磁気リコネクション
1. image2.直接測定可能な物理量は?3. image は直接物理過程を反映しているか?
磁気圏サブストームの磁気リコネクション
1.その場 (in situ) での物理量2. image は得られない3.物理過程のどこの物理量を測定しているか?
磁気圏サブストームの磁気 Reconnection
新しい段階の研究を進めるための方針
多点での同時観測 (理論との融合)
次期磁気圏探査衛星 SCOPE Scale COupling of Plasma Environment
1 親衛星 electron scale 3 子衛星 XYZ方向 MHD scale 1 孫衛星 親の近傍 wave correlation
Magnetic reconnection in the magnetosphere
Magnetotail reconnection (Nightside)
1. Symmetrical(the tail current sheet embedded in the plasma sheet, the tail lobe)
2. Spontaneous (undriven)3. Accumulation of the magnetic field sin the tail lobes4. No preference location (localized, thin current sheet, finite Bn)5. Quasi-steady?6. Trigger process (substorm onset)
Magnetopause reconnection (Dayside)
1. Asymmetric (High-density, Intense-magnetic field, turbulence magnetosheath)2. Forced (driven)3. High-solar wind pressure (intense sheath flows)4. IMF interaction (Bz <0, component merging (sub-solar) vs. anti-parallel merging (near cusp))5. Quasi-steady vs. transient (Flux Transfer Events)6. Solar wind-magnetosphere interaction
オーロラ領域での編隊飛行観測
斜め上から見てオーロラの形状だけでなく鉛直構造も知る
TV-カメラと粒子計測
複数の衛星をGTOにいれた磁場の形状をモニターすると同時に粒子観測