Magnetic Reconnection in the Magnetotail

T. Nagai and M. FujimotoTokyo Institute of Technology

Pre-Geotail Era

Fast plasma flows with Bz < 0 or Bz > 0

Signatures of Magnetic Reconnection

in the MHD level

MHD-code Simulations M. Ugai, T. Sato,…

Pre – Geotail Era

IMP-6October 1972

Hayakawa et al. (1982) Nishida (1984)

The Geotail Era

The first near-Earth tail survey in the 1995/1996 winter season

1. Location of magnetic reconnection for substorm onsets

2. Structure of magnetic reconnection

Onsets on the ground Plasma flows in the tail

Nagai and Machida (1998)

Nagai et al. (1998)

Fast flows for substorm onsets

20 Re 30 Re

Ieda et al. (1998)Machida et al. (1999)Miyashita et al. (1999)Ueno et al. (1999)R. Nakamura (1999)Miyashita et al. (2000)Machida et al. (2000)Miyashita et al. (2001)R. Nakamura et al. (2001)

Ueno et al. (1999)

Location of Magnetic Reconnection

Structure of Magnetic Reconnection

On the basis of velocity distribution functions

Ion and Electron Dynamics

Identify the magnetic reconnection event

Plasmoid at XGSM = -141.51

Machida et al. (1994)

Tailward ions

Tailward electrons

Nagai et al. (1998) Highly Energetic Event

Reconnection Event

Electrons

Ions

Nagai et al. (1998) 1404:59 UT January 27, 1996

Near the Equatorial Plane

Convection Flows V > 2500 km/s

Peak is shifted tailward

Nagai et al. (1998)

Electrons

Ions

1404:34 UT January 27, 1996

Off the Equtorial Plane

Field-Aligned Flows

Inflowing Ions (convection)

Strongly Accelerated

Nagai et al. (1998)

Structure of Magnetic Reconnection

Ions Electrons

Type 　 B

Type 　 N

Nagai et al. (1998)

Electrons

Ions

1406:12 UT January 27, 1996

Outer Boundary Region in Tailward Flows

Tailward Field-Aligned Flows

Inflowing Ions

Inflowing Electrons

Tailward Escaping Electrons

Nagai et al. (1998)

Electrons

Ions

1335:35 UT February 18, 1996

Earthward Field-Aligned Flows

Inflowing Electrons

Earthward Escaping Electrons

Outer Boundary Region For Earthward Flows

Nagai et al. (1998)

Structure of Magnetic Reconnection

Ions Electrons

Type 　 B

Type 　 A

Type 　 N

a part of the Hall current system

The Hall Current System

1. Structure of the current system

2. Current carrier

3. Current density

4. Effect in the magnetic field By

The Hall current system

B. U. O. Sonnerup (1979)

Ion-Electron Decoupling

M.S. Nakamura et al.(1998)

Hybrid simulationfor reconnection

Vex

Nagai et al. (2001)

Reconnectionevent

Nagai et al. (2001)

Electrons for Hall currentsin the December 10, 1996, event

Hoshino (1998)Particle simulation for reconnection

Hall Current density ・・・・ 6 ～ 13 ｎＡ /mNagai et al. (2001)

2

1119:32 UTAugust 3,1996Earthward Flow at XGSM = -10.20

Fujimoto et al. (2001)

1347:19 UTJanuary 10,1995Tailward Flow at XGSM = -46.34

Fujimoto et al. (1997)

Examples of the Hall currents’ Electrons

Earth

Tail

Earth

Tail

By Effect by the Hall current system

Nakabayashi and Machida(1997)

Hoshino (2001)

By > 0

By < 0

By Effect in the Hall current system

Nagai et al. (2001)

The most outer region

+ -+-

Unsolved Questions

With Geotail or with Future Missions

1. Source of anomalous resistivity

2. Ion dynamics near the diffusion region

3. Electron dynamics near the diffusion region

4. Large By magnetic field with large Bz

Source of Anomalous Resistivity

Lower Hybrid Waves ?

Shinohara et al. (1998)

Ion

Electron

February 19, 20011523:02 UT

Complex Ion Distributions

DawnDusk

Ion

Electron

February 10, 20001825:59 UT

Dawn Dusk

Anomalous Electron Distributions

Large By in Earthward Flows

Bz<0

Bz>0

Large negative Bz

1 sec

Future Mission

SCOPE (Scale Coupling in Plasma Environment)

1. High time resolution in particle observations2. Full energy coverage in particle observations3. Multi-point observations to know the s/c location relative to the neutral line