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磁気圏における Magnetic Reconnection

磁気圏における Magnetic Reconnection. ー　 MHD 的描像から粒子的描像へ　－. 長井嗣信 東京工業大学. 地球磁気圏での magnetic reconnection. 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. Dungey model (J. W. Dungey, Phys. Rev. Lett., 6, 47, 1961). Geotail Observations Sun. Solar Wind. Bow Shock. Magetosheath. Magnetopause. Magnetotail.

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磁気圏における Magnetic Reconnection

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  1. 磁気圏におけるMagneticReconnection ー　MHD的描像から粒子的描像へ　－ 長井嗣信 東京工業大学

  2. 地球磁気圏でのmagnetic reconnection 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 Dungey model (J. W. Dungey, Phys. Rev. Lett., 6, 47, 1961)

  3. Geotail Observations Sun Solar Wind Bow Shock Magetosheath Magnetopause Magnetotail

  4. 磁気圏尾部での磁気リコネクションの証拠Geotail以前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 Earthward Flows with Bz > 0 Bz < 0 Fast tailward Flows with Bz < 0 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 Fast Tailward Flows 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

  5. オーロラ爆発の全天カメラ像 a substorm onset (aurora breakup) SIT-TV at Syowa 427.8 nm Kadokura (2002)

  6. 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

  7. Spacecraft Geotail Launch July 22, 1992 Orbit30 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)

  8. Geotail

  9. 磁気リコネクションの観測例 High-Speed Tailward Flowing Ions Bz < 0 Highｌｙ Accelerated Electrons Vx < 0 Ion Electron V=3000km/s EQ off EQ boundary Outflow Ions Convection Heated Inflow Ions High V Outflow Ions XGSM=-28.9 YGSM=5.8 ZGSM=-2.6 RE Less Heated Inflow Ions Low V プラズマの3次元速度分布関数の観測 Outflow Ions

  10. 磁気圏尾部での磁気リコネクションの観測例 Z 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 太陽の方向 X Bx > 0 北半球 Bx < 0　　南半球 Bx =0 赤道面　（電流層）

  11. Distribution Functions Magnetic Field Direction B B B V V V Convection 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)

  12. High-Speed Tailward Flowing Ions Highｌｙ Accelerated Electrons Ion Electron V=3000km/s Boundary off EQ EQ Less Heated Inflow Ions Low V C B A Outflow Ions Heated Inflow Ions High V Outflow Ions Outflow Ions Convection

  13. Magnetotail Reconnection Event High-Speed Tailward Flowing Ions Highｌｙ Accelerated Electrons EQ Magnetic Field Direction B V Convection Ion Electron A near the equatorial plane Outflow Ions Convection

  14. Magnetotail Reconnection Event High-Speed Tailward Flowing Ions Highｌｙ Accelerated Electrons EQ Tailward convection flows with Bz < 0 Vi > 2500 km/s Alfven velocity ~2900 km/s Ion Electron Outflow Ions Convection A near the equatorial plane

  15. Magnetotail Reconnection Event High-Speed Tailward Flowing Ions Highｌｙ Accelerated Electrons Magnetic Field Direction B V Convection Ion Electron B off the equatorial plane

  16. Magnetotail Reconnection Event High-Speed Tailward Flowing Ions Highｌｙ Accelerated Electrons Tailward field-aligned Flows with Bz < 0 V > 2800 km/s Ion Electron B off the equatorial plane

  17. MHD magnetic reconnection simulation (T. Sato, 1979)

  18. 磁気リコネクションの観測例 High-Speed Tailward Flowing Ions Highｌｙ Accelerated Electrons Ion Electron V=3000km/s Boundary off EQ EQ Less Heated Inflow Ions Low V C B A Outflow Ions Heated Inflow Ions High V Outflow Ions Outflow Ions Convection

  19. Distribution Functions Magnetic Field Direction B B B V V V Convection Stationary Field-aligned flows + Convection flows B V// V V// Convection flows with counter-streaming components V

  20. Magnetotail Reconnection Event High-Speed Tailward Flowing Ions Highｌｙ Accelerated Electrons EQ Tailward convection flows with Bz < 0 Vi > 2500 km/s Ve > 4000 km/s ion-electron decoupling Alfven velocity ~2900 km/s Ion Electron V=2500km/s A near the equatorial plane Outflow Ions Convection

  21. Magnetotail Reconnection Event High-Speed Tailward Flowing Ions Highｌｙ Accelerated Electrons off EQ B Ion Electron V=3000km/s Heated Inflow Ions High V Outflow Ions B off the equatorial plane

  22. Magnetotail Reconnection Event High-Speed Tailward Flowing Ions Highｌｙ Accelerated Electrons Ion Electron V=3000km/s Boundary Less Heated Inflow Ions Low V C Outflow Ions C boundary

  23. Magnetotail Reconnection Event High-Speed Tailward Flowing Ions Highｌｙ Accelerated Electrons Ion Electron V=3000km/s Boundary Less Heated Inflow Ions Low V C Outflow Ions Inflowing Electrons Hall Current Electrons C boundary Tailward Escaping Electrons

  24. 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

  25. Classical MHD steady magnetic reconnection Sweet-Parker reconnection Petscheck reconnection reconnection rate

  26. 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

  27. Geospace Environmental Modeling (GEM) Magnetic Reconnection Challenge (Birn et al. J. Geophys. Res., 2001)

  28. 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

  29. 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

  30. Ion-Electron Decoupling at the li Scale - electron + ion Magnetic field + ion - electron electron diffusion region le ion diffusion region li ~ 40 le

  31. ホール電流系の形成 - electron + ion Magnetic field + ion ホール電流 j - electron electron diffusion region le ion diffusion region li ~ 40 le

  32. ホール磁場の形成 　　４重極構造 - electron + ion Magnetic field + ion ホール電流 j - electron ホール磁場 By < 0 electron diffusion region le ion diffusion region li ~ 40 le

  33. ホール電場の形成 - electron + ion Magnetic field E + ion - electron ExBで紙面向こうむきの ドリフト (dawnward motion) electron diffusion region le ion diffusion region li ~ 40 le

  34. 一般化したオームの法則でMHDで無視した項の役割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 • le li b li • 非対角成分　　 1/2 1/2 le = c / wpe5.3/ n (/cc) km li = c /wpi 227/ n (/cc) km V. M. Vasyliunas, Rev. Geophys. Space Phys. 1975 1/2

  35. 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

  36. 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

  37. 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　ｎT 0.01 /cc Alfvén速度　4000 km/s ion inertial length 500 km li = VA / Wi= c / wpi

  38. 2D Full Particle Simulations I. Shinohara me/mi 1/100 Particles 33,554,432 (Av. 128 /grid) Grid Size 512 x 512 Ion Inertial Length 32 grids Electron Inertial Length 3.2 grids Initial Current Thickness 0.5 li (Harris Current Sheet) Double-Periodic Boundary Conditions Results at time Wi t = 18.0

  39. 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

  40. 磁場の分布 南北方向Bz イオンの速度 電子の速度

  41. Magnetotail Reconnection Event High-Speed Tailward Flowing Ions Highｌｙ Accelerated Electrons EQ Tailward convection flows with Bz < 0 Vi > 2500 km/s Ve > 4000 km/s ion-electron decoupling Alfven velocity ~2900 km/s Ion Electron V=2500km/s Outflow Ions Convection

  42. 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

  43. 10 sec Bz = -36 nT tail lobe Bt = 24 nT Bt = 36 nT the 3-min interval the 90-s interval

  44. electron energy spectra Flux strong acceleration of electrons Energy thermal accelerated strong acceleration of electrons

  45. Currents and By The Hall current system

  46. Magnetotail Reconnection Event High-Speed Tailward Flowing Ions Highｌｙ Accelerated Electrons Ion Electron V=3000km/s Boundary Less Heated Inflow Ions Low V C Outflow Ions Inflowing Electrons Hall Current Electrons Tailward Escaping Electrons

  47. Reconnection Event High-Speed Ion Flows Earthward Flows Tailward Flows Highly Accelerated Electrons December 10, 1996

  48. Earthward Tailward Hall Current System Northern hemisphere Southern hemisphere

  49. 2 Hall Current density ・・・・ 6～13 ｎＡ/m

  50. 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

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