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January 19, 2011 Construction of Magnetic Reconnection

January 19, 2011 Construction of Magnetic Reconnection in the near-Earth Magnetotail with Geotail T. Nagai Tokyo Institute of Technology I. Shinohara ISAS/JAXA. MHD Picture of Magnetic Reconnection. inflow. outflow. Bz > 0 Bz < 0.

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January 19, 2011 Construction of Magnetic Reconnection

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  1. January 19, 2011 Construction of Magnetic Reconnection in the near-Earth Magnetotail with Geotail T. Nagai Tokyo Institute of Technology I. Shinohara ISAS/JAXA

  2. MHD Picture of Magnetic Reconnection inflow outflow Bz > 0 Bz < 0

  3. Particle Picture of Magnetic Reconnection Ion flows Electron flows unit ViA unit VeA

  4. Hall Magnetic Fields

  5. Outflows Ve Ve Vi Vi Bz > 0Bz < 0 MHD Ion-electron decoupling MHD

  6. electron current layer - Vey Bz > 0Bz < 0

  7. 15 May 2003 near 1055 UT the spacecraft Geotail at 28 RE in situ observations of magnetic reconnection Geotail

  8. Bz < 0 Bz > 0 Earthward flows Bz > 0Bz < 0 Tailward flows Ion Et Earthward flows Tailward flows

  9. Main Targets of This Paper • 1. Detect the central intense electron current layer • 2. Get scales of magnetic reconnection • with Geotail observations • VA = 2,200 km/s • li = 1,200 km (ion inertial length) • Geotail MGF 16 vectors /s • LEP 12 s • electron g-factor 4x10 • DT 5.5x10 -4 -3

  10. Bz < 0 Bz > 0 Earthward flows 5 minutes Bz > 0Bz < 0 Tailward flows Ion Et Earthward flows Tailward flows

  11. Ion observations Bz > 0Bz < 0 Bz < 0 Bz > 0 Earthward flows 1000 km/s ion flow VA = 2200 km/s Tailward flows

  12. Ion flows vs. electron flows Ion Et Bz > 0Bz < 0 Bz < 0 Bz > 0 Vi Vx > 3000 km/s electron flows Vy > 6000 km/s electron flows Ve Ve

  13. Ion and electron flows perpendicular to the magnetic field Bz > 0Bz < 0 Bz < 0 Bz > 0 V Earthward flows Vx > 2000 km/s electron flows Vy > 3000 km/s electron flows Ve Tailward flows Ve

  14. Electron observations acceleration and heating electron Et Bz > 0Bz < 0 Bz < 0 Bz > 0 V Vx > 2000 km/s electron flows Vy > 3000 km/s electron flows Ve Ve

  15. Bz > 0Bz < 0 Earthward flows Tailward flows 1057:44 1053:44 UT time Earth tail Bz > 0Bz < 0 > 8.47 keV electron directional fluxes

  16. Bz > 0Bz < 0 Earthward flows Tailward flows 1057:44 1053:44 UT time Earth tail Bz > 0Bz < 0 electron velocity distribution function In the equatorial plane Vy < 0 dawnward Vy > 0 duskward

  17. Bz > 0Bz < 0 Earthward flows Tailward flows 1057:44 1053:44 UT time Earth tail Bz > 0Bz < 0 electron velocity distribution function Hall electrons

  18. Bz > 0Bz < 0 Earthward flows Tailward flows 1057:44 1053:44 UT time Earth tail Bz > 0Bz < 0 ion velocity distribution functions

  19. Bz > 0Bz < 0 Earthward flows Tailward flows 1057:44 1053:44 UT time Bz > 0Bz < 0

  20. Bz > 0Bz < 0 Earthward flows Tailward flows time 1057:44 1053:44 UT counter-streaming inflows Bz > 0Bz < 0 ion velocity distribution functions

  21. Important Questions ion-electron decoupling Ve >> Vi MHD MHD large Vey 1057:44 1053:44 UT intense electron current layer spatial scales?

  22. Asymmetric outflows MHD flows +450 km/s -650 km/s Earthward flow speed tailward flow speed

  23. MHD flows +550 km/s -550 km/s (+450 km/s) (-650 km/s) -100 km/s tailward velocity of reconnection site

  24. Asymmetric inflows inflows Vx = +64 km/s Vx= -269 km/s

  25. inflows Cluster results -100 km/s Baker et al. 2002 Imada et al. 2007 Vx = +164 km/s Vx= -169 km/s (+264 km/s -269 km/s) -100 km/s tailward velocity of reconnection site

  26. ion-electron decoupling region MHD MHD 1 li Earth tail central electron current layer 8 li Vx peak Flux peak Ion ele ele ion 8 li = 1.5 RE 1 li = 1200 km

  27. The simulation box size [−Lx/2,+Lx/2]×[−Lz/2,+Lz/2] Lx = 48D Lz = 24D initial current sheet thickness D = 0.5λi Δ is equal to the Debye λi = 200Δ The number of simulation grids 4800×2400 Particle number 1.5×10 particles for each species nCS Ti;CS/Te;CS= 5 nBK= nCSTi;BK = Te;BK= Te;CS ion to electron mass ratio mi/me = 400 frequency ratio ωpe/Ωe = 4, ωpe≡√4πnCSe2/meΩe≡ eB0/mecλi ≡ c/ωpi= c/√4πnCSe2/mi The initial magnetic field the Harris sheet Bx(z) = B0 tanh(z/D) B0 the asymptotic magnetic field D the current sheet half-thickness The perturbed magnetic flux function ψ(x, z) = ψ0 sin(2πx/Lx) cos(2πz/Lz) B (x, z) = eˆy ×∇ψ(x, z) at TΩi = 35 Vi x ∼ 0.3VAVA the Alfven speed B0/√4πminCS 9

  28. the X-line position PIC simulation results the northern earthward side of the reconnection site (upper-left quadrant)

  29. observation simulation at TΩi = 35 Vix / Vex 0.2-0.3 0.1 Vey / Vex 1.25 1.4 Vix 0.5 VA 0.3 VA the full extent of the central 1 li 1 li electron current layer the full extent of 8 li 8 li the ion-electron decoupling region

  30. 8 li = 1.5 RE ion-electron decoupling region Geotail Survey of Tailward Flows with Bz < 0 in 1995-2003 209 events Nagai et al., 2005

  31. Geotail Reconnection Events = Observations of Ion-Electron Decoupling Region 34 events 34/208 = 0.16 reconnection events at 20-30 RE Nagai et al., 1998; 2001

  32. Most of Events are MHD Flows Reconnection Events 34 events 34/208 = 0.16 reconnection events at 20-30 RE 10 RE x 0.16 = 1.6 RE 8 li = 1.5 RE ion-electron decoupling region

  33. ion-electron decoupling region MHD MHD 1 li Earth tail central electron current layer 8 li Vx peak Flux peak Ion ele ele ion 8 li = 1.5 Re 1 li = 1200 km

  34. Main conclusions • In the magnetic reconnection site of the near-Earth magnetotail • the central intense electron current layer 1 li • ion-electron decoupling region 8 li • MHD regions outside the i-e decoupling region • Nagai, T., I. Shinohara, M. Fujimoto, A. Matsuoka, T. Saito, and T. Mukai, • J. Geophys. Res., 116, 2010JA016283, 2011.

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