1. Magnetic reconnection in the magnetotail: Geotail observations T. Nagai Tokyo Institute of Technology World Space Environment Forum 2005 May 4, 2005 Wednesday 09:00 – 09:20 AM

2. Geotail distant tail near tail

3. Geotail Near-Tail Observations 10 x 31 R E orbits Solar Wind Magetosheath Plasma Sheet Bow Shock Magnetopause

4. Nagai et al. (JGR 1998) Ion Electron High-Speed Tailward Flowing Ions High Accelerated Electrons V=3000km/s Inflow Ions Outflow Ions Convection

5. Nagai et al. (1998) Electrons Ions 1406:12 UT January 27, 1996 Outer Boundary Region in Tailward Flows Tailward Field-Aligned Flows Inflowing Ions Inflowing Electrons Tailward Escaping Electrons Hall Currents in Magnetic Reconnection

6. December 10, 1996

7. Nagai et al. (JGR 2001) Electrons for Hall currents in the December 10, 1996, event Hall Current density ・・・・ 6 ～ 13 nA/m 2

8. In Situ Observations of Magnetic Reconnection in 1995 - 1997

9. Solar wind control of the radial distance of the magnetic reconnection site in the magnetotail T. Nagai and M. Fujimoto (Tokyo Institute of Technology) R. Nakamura and W. Baumjohann (OEAW) A. Ieda(Solar-Terrestrial Environment Laboratory) I. Shinohara (ISAS) S. Machida (Kyoto University) Y. Saito and T. Mukai (ISAS)

10. In 1995-1997 Solar Minimum Low B and Low V Solar Maximum High B and High V Solar Wind IMF Bt Velocity

11. Geotail Near-Tail Observations 10 x 31 R E orbits Plasma Sheet (β> 1) X GSM = -10 to -31 R E and Y GSM = -5 to +10 R E

12. Solar Minimum Solar Maximum in 1996-1998in 1999-2003 Even Coverage of X GSM = -10 to -31 R E

13. 1996/02/18 Reconnection Event highly accelerated electrons thermal accelerated electron energy spectra flux energy fast tailward flows with Bz < 0 magnetic field

14. Solar Minimum Solar Maximum in 1996-1998in 1999-2003 X GSM = -25 to -31 R E X GSM = -17 to -31 R E

15. Average Solar Wind Parameters Prior to Each Reconnection Event Total 34 Events SW parameters during 60 minutes prior to each reconnection event

16. Solar Wind Velocity? circles 1996-1998 events black dots1999-2003 events

17. Solar Wind Dynamic Pressure?

18. Southward IMF Bz

19. X = -25 R E circles 1996-1998 events black dots1999-2003 events

20. Solar Wind Energy Input

21. X = -25 R E Near-Tail Midtail

22. Average solar wind parameters for the period from -6 to +2 hours Reconnection Start Time 9 events 25 events Near-tail Midtail

23. Solar Wind Energy Input Near-tail Midtail

24. Near-Tail Midtail Accumulation of Solar Wind Energy Input

25. Solar Wind Velocity Near-Tail Midtail High Velocity 520 km/s Low velocty 460 km/s

26. Solar Wind Dynamic Pressure Near-Tail Midtail 2 nPa high velocity and low density 2 nPa low velocity and high density

27. Near-Tail Midtail Accumulation of Solar Wind Energy Input Solar Wind Input Energy x 2

28. High Efficiency of Solar Wind Energy Input Near-Tail Low Efficiency of Solar Wind Energy Input Midtail Solar Wind Energy Input

29. High Efficiency of Solar Wind Energy Input Low Efficiency of Solar Wind Energy Input Near-Tail Midtail

30. 1. Reconnection event analysis 34 events Tailward flow with Bz < 0 Electron acceleration 2.Tailward flow event analysis 174 events Tailward flow with Bz < 0 No electron acceleration Cluster events at 15-19 R E (from Nakamura et al., GRL 2004)

32. Cluster Near-tail Midtail 15 tailward flows 56 tailward flows 118 tailward flows IMF Bz

33. Cluster Near-tail Midtail Solar Wind Energy Input

34. Cluster Near-tail Midtail Accumulation of Solar Wind Energy Input

35. Past Spacecraft Observations Vela1967-1968Hones et al., 1971; 1973 IMP 61971-1973Hones and Schindler, 1979 ISEE-11980Cattell and Mozer, 1984 ISEE-21978-1979Angelopoulos et al. 1994 CDAW-6McPherron and Manka, 1985 IRM1985-1986Baumjohann et al., 1988,1989,1990,1991 Geotail1996-1998Nagai et al. 1998 1999-2003This study Cluster2001-2002Nakamura et al., 2004

36. Past Spacecraft Observations Vela1967-1968Hones et al., 1971; 1973 at 18 R E 15-18 R E Nishida and Nagayama (1973) …somewhere between X = -10 R E to -25 R E

37. Past Spacecraft Observations ISEE-11980Cattell and Mozer, 1984 ISEE-21978-1979Angelopoulos et al. 1994 CDAW-6McPherron and Manka, 1985 IRM1985-1986Baumjohann et al., 1988,1989,1990,1991 CDAW-613-14 R E Earthward Flows inside 20 R E

38. VELA 15RE IMP-6 ISEE-2 > 22RE ISEE-1 > 21 RE IRM > 18 RE Geotail 1996-1998 > 25 RE Geotail 1999- Cluster 15-30RE

39. Conclusions 1.Reconnection takes place in the near-Earth tail (midtail) under the high (low) solar wind energy input. 2.Controlling factor is efficiency of solar wind input energy, not the total amount of input energy. 3.Tail reconnection site can be controlled by solar cycle variations in the solar wind.

41. 1996 1999 2002 1997 2000 2003 1998 2001 2004

46. Near-Tail Midtail X GSM = -15 to -25 R E X GSM = -25 to -30 R E High Efficiency ofLow Efficiency ofSolar Wind Energy Input

47. VELA 15RE IMP-6 ISEE-2 > 22RE ISEE-1 > 21 RE IRM > 18 RE Geotail 1996-1998 > 25 RE Geotail 1999- Cluster 15-30RE

49. Nagai et al. (1998) Structure of Magnetic Reconnection Ions Electrons Type B Type A Type N a part of the Hall current system

51. Nagai et al. (2001) Reconnection event

52. Hall Current density ・・・・ 6 ～ 13 ｎＡ / m Nagai et al. (2001) 2

55. the 3-min interval the 90-s interval Bz = -36 nT Bt = 36 nT tail lobe Bt = 24 nT 10 sec Event 3 1996/02/18

56. 1996/02/18 Event 48 sechighly acceleration of electrons

58. Hall Currents

72. 170934UT.

73. 174014UT.

74. 180446UT.

77. .

78. .

79. Counterstreaming Ions Magnetic Field Nagai et al., Phys. Plasmas 9, 3705, 2002

80. M. S. Nakamura Hybrid-code Simulation

81. Counterstreaming Ions Magnetic Field Magnetic Reconnection in the Distant Tail Nagai et al., Phys. Plasmas 9, 3705, 2002

82. Tailward flows (< -300 km/s) with Bz < 0 882 events in 1995-2003 Tailward flows (< -300 km/s) with Bz < 0 882 events in 1995-2003 90%