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Magnetic Reconnection in the Earth's Magnetosphere Tatsuki Ogino

Magnetic Reconnection in the Earth's Magnetosphere Tatsuki Ogino Solar-Terrestrial Environment Laboratory, Nagoya University 3-13 Honohara, Toyokawa, Aichi 442-8507, Japan. 複合系の物理. 開放系 磁気圏. 直接作用 対流( Poynting Flux ). 太陽地球システムの特徴. 外への流出. 外からの作用. 窓 磁気リコネクション. 窓 磁気リコネクション. 循環 蓄積.

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Magnetic Reconnection in the Earth's Magnetosphere Tatsuki Ogino

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  1. Magnetic Reconnection in the Earth's Magnetosphere Tatsuki Ogino Solar-Terrestrial Environment Laboratory, Nagoya University 3-13 Honohara, Toyokawa, Aichi 442-8507, Japan

  2. 複合系の物理 開放系 磁気圏 直接作用 対流(Poynting Flux) 太陽地球システムの特徴 外への流出 外からの作用 窓 磁気リコネクション 窓 磁気リコネクション 循環 蓄積 蓄積作用 プラズマ 磁場(電流) 太陽からの作用 エネルギーと物質 光・電磁波 太陽風 惑星間磁場(IMF) 結合系 渦度 沿磁力線電流 降下粒子 重イオン流出 光・電磁波の反射・放射 太陽風 地球起源イオン流出 エネルギー 消費 内部自立系 電磁圏・熱圏 (オーロラ)

  3. 磁気圏と電離圏の 大域的と局所的な 関係を調べる 磁気圏エネルギー 輸送をマクロとミクロな 物理から調べる

  4. Solar Wind and Magnetosphere Interaction Two important mechanism 1. Magnetic reconnection 2. Viscous interaction Kelvin-Helmholtz instability magnetic reconnection >> viscous interaction

  5. 2. Viscous interaction Kelvin-Helmholtz instability(Miura)

  6. 1. Magnetic reconnection Dungey (1961)

  7. Magnetic Reconnection of Earth's Magnetosphere 1. Effect of IMF Bz component southward IMF versus northward IMF Northward IMF Southward IMF

  8. Magnetic reconnection may be the most dominant mechanism. 1. How well the antiparallel field condition is satisfied. 2. How slow the relative velocity between the reconnection magnetic field lines is.

  9. How much can the reconnection process be understood by a superposition of the IMF and geomagnetic field? What are different from a simple superposition? (1) Movement of the reconnection field lines (convection) (2) Configuration of the reconnection region might change remarkably (3) Temporal variation of reconnection process (intermittency)

  10. Simple Superposition of the Geomagnetic Field and IMF Bx>0, By<0, Bz=0 Bx>0, By<0, Bz=-Bx

  11. solar wind Perpendicular flow to magnetopause (normal flow to reconnection line) Parallel flow along magnetopause (convection) MP flow normal to MP flow along MP

  12. Parallel flow along magnetopause (Tailward convection) solar wind normal flow to reconnection line tailword flow convection

  13. Problems of dayside magnetic reconnection in the earth’s magnetosphere • 1. Can the reconnection rate be understood by ? • Where (movement of place, 3D structure) • When (temporal variation) • 2. Can the reconnection potential φMR be distinguished from • the polar cap potential φPC ? • Length of reconnection line (?) • φPC increases when the reconnected magnetic field lines are • carried with the solar wind V , E 3. Total amount of reconnection rate   → Total flux across the open- closed boundary This measure is quite difficult

  14. Where magnetic reconnection occurs in the magnetosphere ・ Antiparallel condition Angle of reconnected field lines, θ Magnitude of reconnected field lines ・ Relative velocity of reconnected field lines ( ) Inclination of the magnetic dipole axis Weakest place of magnitude along the field lines Antiparallel field condition Magnetic equator reconnection line magnetic equator

  15. 2. Effect of IMF By and Bz Two important conditions (1) Anti-parallel field condition (2) Magnetosheath plasma flow How far is the reconnection region from the subsolar point.

  16. θ=60° コンピュータで見るジオスペース 名古屋大学太陽地球環境研究所 共同観測情報センター・教授 荻野竜樹

  17. Southward IMF Northward IMF

  18. 2. Effect of dipole tilt Tilt angle is 30 degrees

  19. 3D Magnetic Field Line Tilt Angle θ=30° Z 15Re Magnetic Equator Southward IMF Bz -5nT X -60Re 15Re -15Re Z 15Re Northward IMF Bz 5nT X -60Re 15Re -15Re

  20. Plasma Pressure Tilt Angle θ=30° Z 30Re Southward IMF Bz -5nT X -120Re 30Re -30Re Z 30Re Northward IMF Bz 5nT X -120Re 30Re -30Re

  21. Plasma Pressure X=-15Re Z 30Re Z 30Re Y Y -30Re 30Re -30Re 30Re -30Re -30Re Southward IMF Bz -5nT Northward IMF Bz 5nT

  22. Comparison of Shape of the Neutral Sheet Between Simulation and Observations by Fairfield and Gosling TAIL BOUNDARY Z 30Re Y -30Re 30Re G -30Re (Gosling et al. 1986 ) Southward IMF Bz -5nT F ・・・Fairfield near –30Re FS ・・・ Fairfield near –20Re G ・・・ Gosling near –15Re

  23. 3D visualization by VRML (Virtual Reality Modeling Language) dipole tilt and southward IMF

  24. Dipole Tilt Southward IMF Magnetic Axis Hinging Distance(10Re) θ Reconnection Point (X=‐10~‐20Re) Hinging Point Magnetic Equator Reconnection Point

  25. dipole tilt and northward IMF

  26. Dipole Tilt Northward IMF Reconnection Point Magnetic Axis Reconnection Point Magnetic Equator

  27. Energy Flux Energy Kinetic Thermal Poynting Kinetic Thermal Magnetic

  28. Energy θ=30° θ=0° 10-3 10-3 Kinetic Thermal エネルギー[J/m] エネルギー[J/m] Energy Magnetic Energy Thermal 0 0 30 0 30 0 X (Re) X (Re)

  29. Energy Flux θ=30° θ=0° 10-4 10-4 tailward Thermal tailward Poynting tailwardKinetic エネルギーフラックス [J/s] エネルギーフラックス [J/s] Energy Flux Energy Flux sunward Poynting 0 0 30 0 30 0 X (Re) X (Re)

  30. 3. Effect of dipole Tilt and IMF By component Tilt angle is 30 degrees Northern hemisphere is smmer

  31. Configuration of 3D magnetic field lines for dipole tilt and IMF By-component

  32. Reconnection for existence of dipole tile and IMF By Divergent flow B IMF From the subsolar point Geomagnetic field Anti-parallel reconnection Magnetic Equator

  33. 12 12 18 06 06 18 00 00 Figure 6.Ionospheric convection and potential in polar region χ= 30 º, θ= 315 º Comparison of throat regions in summer and winter Convection pattern, Energy flux Potential Summer and Northern Hemisphere A Green line is open-closed boundary Winter and Southern Hemisphere

  34. summer - - +- +- + + winter - - Angle of IMF Polar cap potential versus IMF angle (KV) 100 50 0 -50 270° 0 ° 90 ° 180 ° 270 °

  35. Summary 1. A almost closed magnetosphere is formed for pure northward IMF and no dipole tilt because high latitude tail reconnection simultaneously occurs in both hemispheres. 2. If there exists finite IMF By component, the earth's magnetosphere becomes open. 3. When the IMF has small duskward component (Bz>0 and By>0), magnetopause reconnection occurs in dusk side and high latitude region in the northern hemisphere. Open field lines become rich in the dawn polar region because reconnected open field lines convect from dusk to dawn in the dayside polar region. 4. If the dipole tilt exists, the earth's magnetosphere becomes again open even for pure northward IMF and a north-south asymmetry appears. Dayside reconnection occurs near the magnetic equator where the geomagnetic field is weakest along the field lines.

  36. 5. When the dipole tilt and IMF By and Bz components simultaneously exist, a complicated structure without any symmetric plane is formed in the magnetosphere. 6. Anti-parallel reconnection is the primary phenomenon at the dayside magnetopause for a finite By component and southward IMF when the dipole tilt exists. 7. This is because reconnection around the magnetic equator and noon-midnight meridian is suppressed due to poor satisfaction of anti-parallel field condition and increase of magnetosheath flow, and it occurs in the split anti-parallel field regions. 8. Polar convection in throat region becomes more east-west direction in summer hemisphere and that does more noon-midnight direction in winter hemisphere.

  37. 4. Effect of IMF Bx component Parker spiral Earth Sun

  38. Duskward IMF B=15nT,Bx=-By and Bz=0 Bx<0 X Y

  39. B=15nT,Bx=-By and Bz=|Bx| Bx<0 X Y

  40. X Duskward and southward IMF B=15nT,Bx=-By and Bz= -|Bx| Bx<0 Y

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