磁気圏における Magnetic Reconnection

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