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Magnetic Reconnection in the Magnetotail: Geotail Results

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1 Magnetic Reconnection in the Magnetotail: Geotail Results
Tsugunobu Nagai Tokyo Institute of Technology

2 Geotail 1992- IMP-6 ISEE IRM IMP-8 ISEE-3 Tail Geotail

3 Geotail distant tail near tail

4 Large-Scale Structure of the Magnetosphere

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6 Occurrence of Plasma Sheet
Cluster Geotail 静穏時(Kp ≦ 2+) –15 <X<–10 –20 <X<–15 –30 <X<–25 –25 <X<–20 朝側 夕側 Y |Z|

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9 Highly Energetic Event
Reconnection Event 6 Nagai et al. (1998) Highly Energetic Event

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14 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).

15 Event /02/18 quiet period Bz Bt Vx the 60-min interval

16 Event /02/18 10 sec Bz = -36 nT tail lobe Bt = 24 nT Bt = 36 nT the 3-min interval the 90-s interval

17 Event /02/18 strong acceleration of electrons 48 sec

18 Event /02/18 electron energy spectra Flux strong acceleration of electrons Energy thermal accelerated strong acceleration of electrons

19 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

20 1996/02/18 the 3-min interval

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33 Hall Currents

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36 . 170934UT

37 . 174014UT

38 . 180446UT

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43 Counterstreaming Ions
Magnetic Field Nagai et al., Phys. Plasmas 9, 3705, 2002

44 M. S. Nakamura Hybrid-code Simulation

45 Counterstreaming Ions
Magnetic Field Magnetic Reconnection in the Distant Tail Nagai et al., Phys. Plasmas 9, 3705, 2002

46 Tailward flows (< -300 km/s) with Bz < 0 882 events in Tailward flows (< -300 km/s) with Bz < 0 882 events in 90% %

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48 Hall Currents Reconnection

49 Occurrence of Plasma Sheet
Cluster Geotail 擾乱時(Kp ≧ 3–) –15 <X<–10 –20 <X<–15 –30 <X<–25 –25 <X<–20 朝側 夕側 Y |Z|

50 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

51 Occurrence of Plasma Sheet Thinning
朝側 夕側 Y Z Occurrence of Plasma Sheet Thinning 静穏時 擾乱時 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。

52 Occurrence of Plasma Sheet Thinning
朝側 夕側 Y X –3 < Z < 3 静穏時 Cluster 静穏時 Geotail 擾乱時 擾乱時 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

53 dawnとduskでBZが大きい 全体でBZ>0 遠尾部ほどBZが小さい dawn、duskでBZが大きい dawn
地球 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

54 elevation angle(磁力線とXY平面のなす角)で見ると
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

55 遠尾部midnightに集中 遠尾部ではduskにも分布 遠尾部に広く分布 近尾部duskにも分布 dawn-dusk非対称性
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

56 Plasma Sheet (plasma beta > 1) X GSM = -20 to -30 RE YGSM = -10 to +10 RE

57 Solar Wind Plasma Sheet Bs (nT) Btotal (nT) Velocity (km/s)
Density (/cc) Temperature (keV) Solar Wind Plasma Sheet

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60 Solar Wind Plasma Sheet Only Tail Intervals Solar Wind Input VBs
Temperature Solar Wind Plasma Sheet storm

61 Hall Currents Reconnection

62 Geotail 磁気圏尾部の 磁気リコネクションの観測 磁気圏尾部赤道面の近傍のみ XGSM で観測できる
Zns = -3 to +3 Re (Hones (1979) にすでに出ている) XGSM ZNS YGSM YGSM Geotail the first near tail season in

63 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

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