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 12/8/2015 2:51 AM1

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. 12/8/2015 2:51 AM3 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. 12/8/2015 2:51 AM4 Magnetic field structure Outflows (electron Vx and ion Vx) Out-of-plane current (electron Vy and ion Vy) Magnetic Reconnection Simulation

5. 12/8/2015 2:51 AM5 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 12/8/2015 2:51 AM6

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

8. 12/8/2015 2:51 AM8 electron Vx ion Vx ion Vy electron Vy

9. 12/8/2015 2:51 AM9 58 electron Vx ion Vx ion Vy electron Vy electron E-t

10. 12/8/2015 2:51 AM10 -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 12/8/2015 2:51 AM11

12. time Bz > 0 Bz < 0 Tailward flowsEarthward flows Bz > 0 Bz < 0 ion velocity distribution functions 1057:44 1053:44 UT 12/8/2015 2:51 AM12 Earth tail

13. +450 km/s -650 km/s Earthward flow speed tailward flow speed MHD flows 12/8/2015 2:51 AM13 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 12/8/2015 2:51 AM14

15. time Bz > 0 Bz < 0 Tailward flowsEarthward flows Bz > 0 Bz < 0 counter-streaming inflows ion velocity distribution functions 12/8/2015 2:51 AM15

16. Vx = +64 km/s Vx= -269 km/s inflows 12/8/2015 2:51 AM16 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 12/8/2015 2:51 AM17 EarthTail

18. 12/8/2015 2:51 AM18 1 i 8 i 8 i = 1.5 R E 1 i = 1200 km Geotail 15 May 2003 V MR = -100 km/s

19. 12/8/2015 2:51 AM19 0700 UT 05 May 2007

20. 12/8/2015 2:51 AM Ve Vi Magnetic field (MGF) Plasma (LEP) Ion and electron Velocity Number density

21. 12/8/2015 2:51 AM21 electron Vx ion Vx ion Vy electron Vy

22. 12/8/2015 2:51 AM22 Ve Vi Ve electron Vx ion Vx ion Vy electron Vy electron E-t

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 12/8/2015 2:51 AM23

24. 12/8/2015 2:51 AM24 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. 12/8/2015 2:51 AM25 2 1 i 10 i

26. 12/8/2015 2:51 AM26 3D structure of magnetic reconnection Locations of Magnetic Reconnection Events 8 R E dawn-dusk width 10 i