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

Geotail distant tail near tail

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

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

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

December 10, 1996

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

In Situ Observations of Magnetic Reconnection in

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)

In Solar Minimum Low B and Low V Solar Maximum High B and High V Solar Wind IMF Bt Velocity

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

Solar Minimum Solar Maximum in in Even Coverage of X GSM = -10 to -31 R E

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

Solar Minimum Solar Maximum in in X GSM = -25 to -31 R E X GSM = -17 to -31 R E

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

Solar Wind Velocity? circles events black dots events

Solar Wind Dynamic Pressure?

Southward IMF Bz

X = -25 R E circles events black dots events

Solar Wind Energy Input

X = -25 R E Near-Tail Midtail

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

Solar Wind Energy Input Near-tail Midtail

Near-Tail Midtail Accumulation of Solar Wind Energy Input

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

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

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

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

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

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 R E (from Nakamura et al., GRL 2004)

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

Cluster Near-tail Midtail Solar Wind Energy Input

Cluster Near-tail Midtail Accumulation of Solar Wind Energy Input

Past Spacecraft Observations Vela Hones et al., 1971; 1973 IMP Hones and Schindler, 1979 ISEE-11980Cattell and Mozer, 1984 ISEE Angelopoulos et al CDAW-6McPherron and Manka, 1985 IRM Baumjohann et al., 1988,1989,1990,1991 Geotail Nagai et al This study Cluster Nakamura et al., 2004

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

Past Spacecraft Observations ISEE-11980Cattell and Mozer, 1984 ISEE Angelopoulos et al CDAW-6McPherron and Manka, 1985 IRM Baumjohann et al., 1988,1989,1990,1991 CDAW R E Earthward Flows inside 20 R E

VELA 15RE IMP-6 ISEE-2 > 22RE ISEE-1 > 21 RE IRM > 18 RE Geotail > 25 RE Geotail Cluster 15-30RE

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.

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

VELA 15RE IMP-6 ISEE-2 > 22RE ISEE-1 > 21 RE IRM > 18 RE Geotail > 25 RE Geotail Cluster 15-30RE

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

Nagai et al. (2001) Reconnection event

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

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

1996/02/18 Event 48 sechighly acceleration of electrons

Hall Currents

170934UT.

174014UT.

180446UT.

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

M. S. Nakamura Hybrid-code Simulation

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

Tailward flows (< -300 km/s) with Bz < events in Tailward flows (< -300 km/s) with Bz < events in %