Magnetic Reconnection in the Magnetotail
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Magnetic Reconnection in the Magnetotail
T. Nagai and M. FujimotoTokyo Institute of Technology
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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,…
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Pre – Geotail Era
IMP-6October 1972
Hayakawa et al. (1982) Nishida (1984)
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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
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Nagai and Machida (1998)
Nagai et al. (1998)
Fast flows for substorm onsets
20 Re 30 Re
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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
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Structure of Magnetic Reconnection
On the basis of velocity distribution functions
Ion and Electron Dynamics
Identify the magnetic reconnection event
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Plasmoid at XGSM = -141.51
Machida et al. (1994)
Tailward ions
Tailward electrons
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Nagai et al. (1998) Highly Energetic Event
Reconnection Event
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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
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Nagai et al. (1998)
Electrons
Ions
1404:34 UT January 27, 1996
Off the Equtorial Plane
Field-Aligned Flows
Inflowing Ions (convection)
Strongly Accelerated
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Nagai et al. (1998)
Structure of Magnetic Reconnection
Ions Electrons
Type B
Type N
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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
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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
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Nagai et al. (1998)
Structure of Magnetic Reconnection
Ions Electrons
Type B
Type A
Type N
a part of the Hall current system
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The Hall Current System
1. Structure of the current system
2. Current carrier
3. Current density
4. Effect in the magnetic field By
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The Hall current system
B. U. O. Sonnerup (1979)
Ion-Electron Decoupling
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M.S. Nakamura et al.(1998)
Hybrid simulationfor reconnection
Vex
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Nagai et al. (2001)
Reconnectionevent
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Nagai et al. (2001)
Electrons for Hall currentsin the December 10, 1996, event
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Hoshino (1998)Particle simulation for reconnection
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Hall Current density ・・・・ 6 ~ 13 nA /mNagai et al. (2001)
2
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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
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By Effect by the Hall current system
Nakabayashi and Machida(1997)
Hoshino (2001)
By > 0
By < 0
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By Effect in the Hall current system
Nagai et al. (2001)
The most outer region
+ -+-
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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
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Source of Anomalous Resistivity
Lower Hybrid Waves ?
Shinohara et al. (1998)
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Ion
Electron
February 19, 20011523:02 UT
Complex Ion Distributions
DawnDusk
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Ion
Electron
February 10, 20001825:59 UT
Dawn Dusk
Anomalous Electron Distributions
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Large By in Earthward Flows
Bz<0
Bz>0
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Large negative Bz
1 sec
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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