Chapman Conference “Fundamental Properties and Processes of Magnetotails” 12 March 2013, Tuesday, 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 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)

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)

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

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

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

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

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.

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

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

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

+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

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

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

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 Imada et al tailward velocity of reconnection site 6/27/2016 6:53 PM17 EarthTail

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

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

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

6/27/2016 6:53 PM22 Ve Vi Ve electron Vx ion Vx ion Vy electron Vy

Vx = km/s Vx= km/s (+375 km/s -500 km/s) km/s tailward velocity of reconnection site 6/27/2016 6:53 PM23

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

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, Zenitani, S., I. Shinohara, and T. Nagai, Geophys. Res. Lett., 39, L11102, /27/2016 6:53 PM i 10 i

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

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

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

observationsimulation at TΩi = 35 Vix / Vex Vey / Vex 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

6/27/2016 6:53 PM30 30 Magnetic Reconnection Events In

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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 5.5x /27/2016 6:53 PM41

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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

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 UT 6/27/2016 6:53 PM46 Earth tail

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

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.