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Chapman Conference “Fundamental Properties and Processes of Magnetotails”

Chapman Conference “Fundamental Properties and Processes of Magnetotails” 12 March 2013, Tuesday, 1205-1220 p.m. Structure of Magnetic Reconnection in the Earth’s Magnetotail Geotail Observations T. Nagai Tokyo Institute of Technology. Launch on 24 July 1992.

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Chapman Conference “Fundamental Properties and Processes of Magnetotails”

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  1. Chapman Conference “Fundamental Properties and Processes of Magnetotails” 12 March 2013, Tuesday, 1205-1220 p.m. Structure of Magnetic Reconnection in the Earth’s Magnetotail Geotail Observations T. Nagai Tokyo Institute of Technology

  2. Launch on 24 July 1992 20th Anniversary of Geotail Observations Prof. Atsuhiro Nishida “Person of Cultural Merit” in 2012 (an official Japanese recognition and honor)

  3. 20-year Geotail observations 2 clear-cut encounters of the magnetic reconnection site observation observation time probability ion-electron decoupling region 336 s 0.000,000,53 (96+240) electron diffusion region 36 s 0.000,000,057 (12+24)

  4. Magnetic Reconnection Simulation Magnetic field structure Outflows (electron Vx and ion Vx) Out-of-plane current (electron Vy and ion Vy)

  5. 15 May 2003 1055 UT

  6. Bz < 0 Bz > 0 Earthward flows 5 minutes Bz > 0Bz < 0 Tailward flows ion energy-time diagrams Earthward flows Tailward flows

  7. Magnetic field (MGF) Plasma (LEP) Ion and electron Velocity Number density Vi Vi Vi Vi Ve Ve Ve Ve

  8. electron Vx ion Vx ion Vy electron Vy

  9. electron Vx ion Vx ion Vy electron Vy 58

  10. +vix -vix -vex +vex S. Zenitani, I. Shinohara, and T. Nagai, Geophys. Res. Lett., 39, L11102, 2012. Direct detection of the dissipation region

  11. Spatial Scales ion-electron decoupling Ve >> Vi MHD MHD large Vey 1057:44 1053:44 UT intense electron current layer

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

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

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

  15. Bz > 0Bz < 0 Earthward flows Tailward flows time counter-streaming inflows Bz > 0Bz < 0 ion velocity distribution functions

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

  17. inflows Earth Tail 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

  18. Geotail 15 May 2003 1 li 8 li VMR = -100 km/s 8 li = 1.5 RE 1 li = 1200 km

  19. 05 May 2007 0700 UT

  20. Magnetic field (MGF) Plasma (LEP) Ion and electron Velocity Number density Vi Vi Vi Vi Ve Ve Ve Ve

  21. Ve Vi Vi Ve

  22. Ve Vi Vi Ve electron Vx ion Vx ion Vy electron Vy

  23. Vx = +437.5 km/s Vx= -437.5 km/s (+375 km/s -500 km/s) -62.5 km/s tailward velocity of reconnection site

  24. 1 li 13 li VMR = -62.5 km/s 8 li = 1.5 RE 1 li = 1200 km

  25. Main conclusions • In the magnetic reconnection site of the near-Earth magnetotail • the central intense electron current layer (10 nA/m ) 1 li • ion-electron decoupling region 10 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, A04222, 2011. • Zenitani, S., I. Shinohara, and T. Nagai, • Geophys. Res. Lett., 39, L11102, 2012. 2 1 li 10 li

  26. 3D structure of magnetic reconnection Locations of Magnetic Reconnection Events 10 li 8 RE dawn-dusk width

  27. Structure of electron jets in magnetic reconnection Locations of Magnetic Reconnection Events MHDion-electron decoupling out-of-plane current

  28. Structure of electron jets in magnetic reconnection Bz turning Locations of Magnetic Reconnection Events MHD

  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. 30 Magnetic Reconnection Events In 1996-2012

  31. Main Targets of This Paper • Detect the central intense electron current layer • 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

  32. 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

  33. 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

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

  35. MHD flows Vi = Ve Errors are small when energetic electrons are rich. electron Vx ion Vx electron Vy ion Vy

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