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. NagaiTokyo Institute of Technology 6/27/2016 6:53 PM1

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

3. 6/27/2016 6:53 PM3 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. 6/27/2016 6:53 PM4 Magnetic field structure Outflows (electron Vx and ion Vx) Out-of-plane current (electron Vy and ion Vy) Magnetic Reconnection Simulation

5. 6/27/2016 6:53 PM5 1055 UT 15 May 2003

6. Tailward flows Earthward flows Bz 0 Tailward flows Earthward flows ion energy-time diagrams 5 minutes Bz > 0 Bz < 0 6/27/2016 6:53 PM6

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

8. 6/27/2016 6:53 PM8 electron Vx ion Vx ion Vy electron Vy

9. 6/27/2016 6:53 PM9 58 electron Vx ion Vx ion Vy electron Vy

10. 6/27/2016 6:53 PM10 -v ix +v ix +v ex -v ex Direct detection of the dissipation region S. Zenitani, I. Shinohara, and T. Nagai, Geophys. Res. Lett., 39, L11102, 2012.

11. ion-electron decoupling Ve >> Vi intense electron current layer large Vey Spatial Scales MHD 1057:44 1053:44 UT 6/27/2016 6:53 PM11

12. time Bz > 0 Bz < 0 Tailward flowsEarthward flows Bz > 0 Bz < 0 ion velocity distribution functions 1057:44 1053:44 UT 6/27/2016 6:53 PM12 Earth tail

13. +450 km/s -650 km/s Earthward flow speed tailward flow speed MHD flows 6/27/2016 6:53 PM13 Asymmetric MHD outflows

14. +550 km/s -550 km/s (+450 km/s) (-650 km/s) -100 km/s MHD flows tailward velocity of reconnection site 6/27/2016 6:53 PM14

15. time Bz > 0 Bz < 0 Tailward flowsEarthward flows Bz > 0 Bz < 0 counter-streaming inflows ion velocity distribution functions 6/27/2016 6:53 PM15

16. Vx = +64 km/s Vx= -269 km/s inflows 6/27/2016 6:53 PM16 Asymmetric inflows

17. Vx = +164 km/s Vx= -169 km/s (+264 km/s -269 km/s) -100 km/s inflows Cluster results -100 km/s Baker et al. 2002 Imada et al. 2007 tailward velocity of reconnection site 6/27/2016 6:53 PM17 EarthTail

18. 6/27/2016 6:53 PM18 1 i 8 i 8 i = 1.5 R E 1 i = 1200 km Geotail 15 May 2003 V MR = -100 km/s

19. 6/27/2016 6:53 PM19 0700 UT 05 May 2007

20. 6/27/2016 6:53 PM Ve Vi Magnetic field (MGF) Plasma (LEP) Ion and electron Velocity Number density

21. 6/27/2016 6:53 PM21 Ve Vi Ve

22. 6/27/2016 6:53 PM22 Ve 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 6/27/2016 6:53 PM23

24. 6/27/2016 6:53 PM24 8 i = 1.5 R E 1 i = 1200 km V MR = -62.5 km/s 1 i 13 i

25. Main conclusions In the magnetic reconnection site of the near-Earth magnetotail 1.the central intense electron current layer (10 nA/m ) 1 i 2.ion-electron decoupling region 10 i 3.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. 6/27/2016 6:53 PM25 2 1 i 10 i

26. 6/27/2016 6:53 PM26 3D structure of magnetic reconnection Locations of Magnetic Reconnection Events 8 R E dawn-dusk width 10 i

27. 6/27/2016 6:53 PM27 Structure of electron jets in magnetic reconnection Locations of Magnetic Reconnection Events MHD ion-electron decoupling out-of-plane current

28. 6/27/2016 6:53 PM28 Structure of electron jets in magnetic reconnection Locations of Magnetic Reconnection Events Bz turning MHD

29. observationsimulation at TΩi = 35 Vix / Vex0.2-0.30.1 Vey / Vex1.251.4 Vix0.5 V A 0.3 V A the full extent of the central1 i 1 i electron current layer the full extent of 8 i 8 i the ion-electron decoupling region 6/27/2016 6:53 PM29

30. 6/27/2016 6:53 PM30 30 Magnetic Reconnection Events In 1996-2012

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41. Main Targets of This Paper 1.Detect the central intense electron current layer 2.Get scales of magnetic reconnection with Geotail observations  V A = 2,200 km/s  i = 1,200 km (ion inertial length) Geotail MGF16 vectors /s LEP12 s electron g-factor 4x10  T 5.5x10 -4 -3 6/27/2016 6:53 PM41

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45. 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 number1.5×10 particles for each species n CS Ti; CS /Te; CS = 5 n BK = n CS Ti;BK = Te; BK = Te; CS ion to electron mass ratio mi/me = 400 frequency ratio ωpe/Ωe = 4, ω pe ≡√4πn CS e2/m e Ω e ≡ eB 0 /m e c λi ≡ c/ω pi = c/√4πn CS e2/m i The initial magnetic field the Harris sheet Bx(z) = B 0 tanh(z/D) B 0 the asymptotic magnetic field D the current sheet half-thickness The perturbed magnetic flux function ψ(x, z) = ψ 0 sin(2πx/Lx) cos(2πz/Lz) B (x, z) = eˆy × ∇ ψ(x, z) at TΩi = 35 Vi x ∼ 0.3V A V A the Alfven speed B 0 /√4πm i n CS 9 6/27/2016 6:53 PM45

46. time Bz > 0 Bz < 0 Tailward flowsEarthward flows Bz > 0 Bz < 0 Vy < 0 dawnward Vy > 0 duskward electron velocity distribution function In the equatorial plane 1057:44 1053:44 UT 6/27/2016 6:53 PM46 Earth tail

47. time Bz > 0 Bz < 0 Tailward flowsEarthward flows Bz > 0 Bz < 0 Hall electrons electron velocity distribution function 1057:44 1053:44 UT 6/27/2016 6:53 PM47 Earth tail

48. 6/27/2016 6:53 PM48 electron Vx ion Vx electron Vy ion Vy MHD flows Vi = Ve Errors are small when energetic electrons are rich.