Evidence for the dissipation region
in magnetotail reconnection
Seiji Zenitani (NAOJ)
Iku Shinohara (JAXA/ISAS), Tsugunobu Nagai (Tokyo Tech)
Ackn: M. Hesse, A. Klimas, M. Kuznetsova, C. Black (NASA/GSFC)

Outline•1. Introduction & theory•2. Structure of kinetic reconnection– (SZ, M. Hesse, A. Klimas, M. Kuznetsova, C. Black 2011)•3. Geotail observation– (SZ, T. Nagai, I. Shinohara 2012)– The 2003-05-15 event– Dissipation region (De)– EFD measurement in depth– Brief comparison with theory– Lorentz work (W)•4. Summary

1. Introduction

The dissipation region• The ideal condition• We expected a multi-scale structure

Ion Dissipation Region
Electron DissipationRegion (EDR)

ZX• We are interested in the innermost EDR– It is traditionally identified byWhere is the dissipation region?
Magnetotail reconnection

Z

Nonideal layer stretches
in the outflow directions+Bz

Magnetopause reconnection

-BzBy
ZX

Pritchett & Mozer 2009 PoPX

Karimabadi+ 2007 GRL

In a kinetic plasma,nonidealness ≠magnetic dissipation

Total energy
transfer
Generalizeddissipation
measure[Zenitani et al. 2011 PRL]Work by Lorentz force (Ideal MHD)

Birn & Hesse 2005

Nonideal energy transfer

Two elements : jμ and eμ• Spacelike current• Covariant electric field

4-currentElectron fluid 4-velocity

Electromagnetic tensor

... in the moving frame of electrons• Spacelike current
Electric current in this frame• Covariant electric field
Electric field in this frame• Their contraction
Energy transfer fromthe electromagnetic field
to plasmas

Electron-frame dissipation measure– ( j . E ) in the electron’s fluid frame– Unique quantity in a unique frame ⇒ Lorentz invariant• Di: ( j . E ) in the ion’s fluid frame• Dmhd : ( j . E ) in the nonrelativistic MHD frame• Useful relation →• Dmhd > 0 indicates the conventional “magnetic dissipation.”
Zenitani+ 2011 PRL

Nonidealness: (E + vexB)y ≠ 0AntiparallelZ

Guide-field

Symmetric Rx

Z

Asymmetric Rx

XX-+

The new measure: De

AntiparallelZ

Guide-field

Symmetric Rx

Z

Asymmetric Rx

Dissipation RegionXX

2. Structure of kinetic
reconnectionStructure of kinetic reconnection
ZpYX

e-Magnetic field lines from
2D kinetic (PIC) simulation+By (Quadrupole field)

Structure of kinetic reconnection
Dissipation Region

ZYBy (Quadrupole field)

e-XJJp+X
e-Outflow velocity -- electron overshoot
50-5

vix
vex

vixvexe-Electron shock (1/2)• Electron jet hits a shock-like
transition region,
where unmagnetizedelectrons get magnetizedelectronshockvex
ZX
v10ex

1

80.8

60.6

40.4

magnetizedelectrons

unmagnetizedelectrons
2038

410.2

44

4750

53056

10Reconnected Bz180.8

60.6

40.4

20.2038414447

X

50

53

t=42
t=40
t=38
t=36

056

Zenitani+ 2011 PoPElectron shock (2/2)
Bymagnetic cavity

vex

Unmagnetized ionsunmagnetizedelectrons
magnetizedelectrons

Hall physics• Sudden field-line bending at the electron shockA map of dissipation

Shock dissipation

Reconnection dissipation
De<0Dmhd<0:anti-dissipation
X• Two dissipation regions• The electron jet is anti-dissipative, although it was often called“outer electron dissipation [diffusion] region” in late 2000’s.

Composition of the dissipation measure• z-term↑ Inflow cut
0.1• Minor in antiparallel
configuration

0.05
0De
Jy E'yJz E'z-0.05
rho_c (ve . E)
-1

-0.5

00.5

1

• Minor for realistic(wpe/wce) parameters→ Outflow
0.1 cut0.05
0De-0.05
Jx E'xJy E'y-0.1
32• Charge-term

34

36

38

40

4244

Approximate measure
De : Electron-frame dissipation measure

De* : Approximate form

• Note: An ion version D*i does not work. Only D*e works.

3. Observation

Structure of kinetic reconnectionDissipation Region

ZY

By (Quadrupole field)

e-X

JJp+Xe-Outflow velocity -- electron overshoot50-5vixvex

vixvexe-GEOTAIL

20YEARS• 12s datasets• LEP 3D moment data (ni, vi, ve)• EFD data (Ex, Ey)• MGF data (B)Electron jet events

+vix

-vix

+vex

-vex
ve⊥x

2007-05-05
3000
2000
1000
0vi x

-1000
-2000
-3000
-4000
658

660

662

664

666

• Only three events with electron overshoot in2000s : 2003-05-15, 2007-05-05, 2010-08-28

668• c.f. Outflow crossing(Phan et al. 2007)

The 2003-05-15 event [Nagai et al. 2011 JGR]
Bz reversal• The best reconnection event ever• 15 May 2003, 1050 - 1100 UT• (X, Y, Z) = (-27.8, +3.3, +3.5 RE)
Bz

Plasma velocity [km/s]

2003-05-15

3000
2000

V⊥x (ion)V⊥x (electron)

1000
0-1000
-2000

1053

1054

1055
1056
1057
Time [UT] - 15 May 2003

Bz reversal

1058

-3000

Nonideal dissipation
Approximate measure
Dissipation [pWm-3]

Plasma velocity [km/s]
3000

60
De* (raw 105745)
V⊥x (ion)V⊥x (electron)

1000• LEP moment dataJ = eni (vi-ve)

0• EFD data (Ex, Ey)-20-1000• MGF data (B)

-40

-2000
Another-3000
dissipation1058
region?

4020

2000

0-60
1053

1054

10551056
1057
Time [UT] - 15 May 2003

Simulation
0.1
0.05

Devix
vex

0-0.05-525-vix

+vex

-vex

50-0.120+vix303540455055

EFD instrument

e-e-e-100m• 1 spin = 3 sec

Tsuruda+ 1994

Photoelectrons

EFD data during 1057:45UT-1057:58UT
EFD raw dataExtreme
subspin burst
ΔE ~ 50mV/m• We examine EFD raw data throughout the 2003-05-15 event• We correct E by dropping two invalid 3s-dataNonideal dissipation
Approximate measure
Dissipation [pWm-3]

Plasma velocity [km/s]

60

3000
De* (raw 105745)
V⊥x (ion)V⊥x (electron)

40
20

2000
1000

00-20

-1000

-40

-2000

-60
1053

1054

1055
1056
1057
Time [UT] - 15 May 2003

Simulation
0.10.05

Devix
vex

0-0.05

-525

1058

+vix

-vix

+vex

-vex

50-0.1
20

Corrected
Strange-3000

30

3540

455055

Ex correction (not incorporated)
EFD electric field data
Ex2.29 mV/mE corrected

Originalx[pWm-3]
Plasma velocity [km/s]Dissipation

Dissipation [pWm-3]
60
40
20

De*V⊥x (ion)V⊥x (electron)

0

3000

60

2000

40

1000

2000

Plasma velocity [km/s]
3000

De* (offset)V⊥x (ion)V⊥x (electron)

2000
1000
0-20

-1000

-20

-1000

-40

-2000

-40

-2000

-3000

-60
1053

-60
1053

1054

1055
1056
1057
Time [UT] - 15 May 2003

1058

• Key signatures are unchanged

1054

1055
1056
1057
Time [UT] - 15 May 2003

1058

-3000

Observation vs Theory• Observation• Retreat speed: ~100 [km/s] (Nagai et al.) → Length: 2400-3600 [km]• Dissipation rate: 45 [pWm-3]• Theory

Dissipation [pWm-3]• Length (20deloc): 1000-2000 [km]60

• Dissipation rate: <160 [pWm-3]

20• In reasonable agreement

40-vix+vex-vex

3000
De*V⊥x (ion)V⊥x (electron)

2000
1000

00

-20

-1000

-40

-2000

-60
1053

+vix

Plasma velocity [km/s]

1054

1055
1056
1057
Time [UT] - 15 May 2003

1058

-3000

We have ONLY 3 events in late-2000s. Why?
• Volume problem

1~2deShorter at a realistic mass ratio:
Overemphasized by artificiallyheavy electrons• Slow crossing needed for
GeotailLorentz work
Total energy transfer

Work by Lorentz force (Ideal MHD)

Nonideal energy transfer

Lorentz work: WL = ( j x B ). vi
Geotail
Dissipation [pWm-3]

PIC simulation: 1D cut
65 [pWm ]-3

Plasma velocity [km/s]

60

3000

40

2000

20

1000

00-20

-1000

-40

-2000

-60
1053

-3000

1054

1055
1056
1057
Time [UT] - 15 May 2003

1058

0.04

864
20-2-4-6-8
100.020-0.022030

4050

PIC simulation: 2D snapshot• Positive over reconnection region• Strong at a dipolarization front(tangential discontinuity)

60-0.04

Summary• Lorentz-invariant measure De for the dissipation region• Geotail observation of M’tail reconnection on 2003-05-15• Reconnection signatures– Plasma flow
• → Electron overshoot– Approximate measure D*e• → Dissipation region

+vix

-vix

– Lorentz work WL• → Dipolarization front+vex-vex• Observation vs Theory: Reasonable• First detection of the dissipation region in a planetary M’tailTak for din opmærksomhed!

• I am eagerly waiting for MMS!!
– Better time resolution, 3 components of E

Tak for din opmærksomhed!

Zenitani, Shinohara, & Nagai, Geophys. Res. Lett., 39, L11102 (2012)