Magnetic Reconnection in the
Magnetotail: Geotail Results
Tsugunobu Nagai
Tokyo Institute of Technology
Geotail
1992-
IMP-6
IMP-8
ISEE
IRM
ISEE-3 Tail
Geotail
Geotail
distant tail
near tail
Large-Scale Structure of the Magnetosphere
Occurrence of Plasma Sheet
Cluster
Geotail
静穏時(Kp ≦ 2+)
–15 <X<–10
–20 <X<–15
–25 <X<–20
|Z|
Y 夕側
–30 <X<–25
朝側
|Z|
Reconnection Event
Nagai et al. (1998)
Highly Energetic Event
the first onset of the second substorm
1996/02/18
two multiple-onset substorms
with similar magnitudes
The Hall current of the first substrom
is discussed in J. Geophys. Res. (2001).
Event 3 1996/02/18
quiet period
Bz
Bt
Vx
the 60-min interval
Event 3 1996/02/18
10 sec
Bz = -36 nT
tail lobe
Bt = 24 nT
the 3-min interval
Bt = 36 nT
the 90-s interval
Event 3 1996/02/18
strong acceleration of electrons
48 sec
electron energy spectra
Event 3 1996/02/18
Flux
strong acceleration
of electrons
Energy
thermal
accelerated
strong acceleration of electrons
Particle-code simulation
for magnetic reconnection
by I. Shinohara
Bz ~ lobe Bt
10 sec
Bz = -36 nT
tail lobe
Bt=24 nT
Bt = 36 nT
the 90-s interval
1996/02/18
the 3-min interval
Hall Currents
.
170934UT
.
174014UT
.
180446UT
.
.
Counterstreaming Ions
Magnetic Field
Nagai et al., Phys. Plasmas 9, 3705, 2002
M. S. Nakamura
Hybrid-code Simulation
Counterstreaming Ions
Magnetic Field
Magnetic Reconnection in the Distant Tail
Nagai et al., Phys. Plasmas 9, 3705, 2002
90%
Tailward flows
(< -300 km/s)
with Bz < 0
Tailward flows
(< -300 km/s)
with Bz < 0
882 events
in 1995-2003
882 events
in 1995-2003
90%
Hall Currents
Reconnection
Occurrence of Plasma Sheet
Cluster
Geotail
擾乱時(Kp ≧ 3–)
–15 <X<–10
–20 <X<–15
–25 <X<–20
|Z|
Y 夕側
–30 <X<–25
朝側
|Z|
Occurrence of Plasma Sheet
Active Times vs. Quiet Times
擾乱時のプラズマシートは・・・
midnightで薄く、朝夕両側で厚い
静穏時よりも薄い
全体的に静穏時より出現率が小さい
擾乱時(Kp ≧ 3–)
Geotail
静穏時(Kp ≦ 2+)
Geotail
Z
Occurrence of Plasma Sheet Thinning
静穏時
Geotail
–20 <X<–10
–30 <X<–20
Cluster
–20 <X<–10
 ニュートラルシート(Z=0)付近で起こるイベントは、
近尾部側、とくに静穏時では少ない。
Y夕側
擾乱時
朝側
朝側
Occurrence of Plasma Sheet Thinning
X
夕側
–3 < Z < 3
静穏時
Geotail
擾乱時
Y
静穏時
Cluster
静穏時では、イベントの発生がmidnightおよび夕側に偏っている
尾部側へ向かってイベントが増加する
擾乱時
1.
dawnとduskでBZが大きい
dawn
静穏時(Kp≦2+)
• 全体でBZ>0
• 遠尾部ほどBZが小さい
• dawn、duskでBZが大きい
地球
dusk
elevation angle(磁力線とXY平面のなす角)で見ると
 BZ 
  asin 
 B 
• BZで見るよりはっきりと
dawn、duskで大きい
• 遠尾部ほど小さい
静穏時(Kp≦2+)
• 遠尾部midnightに集中
• 遠尾部ではduskにも分布
擾乱時(Kp≧3-)
• 遠尾部に広く分布
• 近尾部duskにも分布
• dawn-dusk非対称性
Plasma Sheet (plasma beta > 1)
X GSM = -20 to -30 RE
YGSM = -10 to +10 RE
Solar Wind
Bs (nT)
Btotal (nT)
Velocity (km/s)
Density (/cc)
Density (/cc)
Plasma Sheet
Temperature (keV)
Velocity (km/s)
Only Tail Intervals
Solar Wind
storm
Solar Wind Input VBs
Plasma Sheet
Temperature
Hall Currents
Reconnection
磁気圏尾部の
磁気リコネクションの観測
XGSM
磁気圏尾部赤道面の近傍のみ
で観測できる
ZNS
YGSM
Zns = -3 to +3 Re
(Hones (1979) にすでに出ている)
Geotail
the first near tail season
in 1995-1996
YGSM
磁気リコネクションの観測例
Flow Reversal
Minimum B near Flow Reversal
Bz>0
Bz<0
Vx>0
Bz=10nT
Vx<0
Bt=0.25 nT
ダウンロード

Magnetic Reconnection in the Magnetotail: Geotail Results