Asymmetricreconnection
不揃いなリコネクション

Seiji Zenitani

M’pause reconnection: asymmetry
MPM’pause

solarwindPhan+ 2013
Phan & Paschmann 1996

Early predictions

thae’shM
MP

Petschek & Thorne 1967

M’sphere
M’sheath

Levy+ 1964

M’sphere

Sonnerup & Teh 2008

• Rotational discontinuity (RD) and slow-mode expansion fan (SEF) are expected• See Lin & Lee 1993 for detail.

Numerical development
HybridMHD

Nakamura & Scholer 2000

PIC
Hoshino & Nishida 1983

• Shock structures are roughly confirmed-Swisdak+ 2003

Minor details were difficult to tell: schemes, limited domain, and kinetic effects• Steep RD and downstream bulge on the M’sheath side

Renewed attention in late 00’s

• NASA MMS mission• 4 satellites• Extremely high resolution• Everything is ON SCHEDULE• Launch for Oct 2014
• During Phase 1 (2015-2016),
MMS will probe RX sites atthe M’pause

Basics properties in symmetric RX
Bin ρin Vin

L E

Energy conservation

Continuity© H. Odaδ

Bout
ρout pout
Vout
R ~ Vin / VA,in ~ 0.1
E ~ 0.1VA,inBin
Vout ~ VA,inDawn of the new MHD theory• Scaling analysis of different
upstream densities• Empirical hybrid relations

Borovsky+ 2007

Cassak=Shay model (1/2)• Immediate success• Full asymmetry• Conservation analysis• Useful hybrid relations

Cassak & Shay 2007

E ~ 0.1 vA B0vout ~ vA

Cassak=Shay model (2/2)• Too good to be true?
• Minor differences aside,
the results were verified bymany simulation works(Cassak & Shay 2007-2009,Malakit+ 2010)

Compressibility debate• Cassak=Shay balances• We became aware of the roles of- Compressibility- Enthalpy flux- ==> Missing pieces in Sweet-Parker theories.

• Theory (Birn+ 2010, 2011, Hesse+2011)• Simulation (Birn+ 2008, Aunai+ 2011)• Observation (Eastwood+ 2013)

Birn+ (2010) model• Consider the full balance equations, including the compressibility• Near-equipartition• Compression factor

Kinetic signatures in symmetric RX
Magnetic cavities

ByEz

y+3z-3
25.6
38.4

x

"Flipped" field lines
51.2

Zenitani et al., PoP 18, 122108 (2011)• Flipping of the filed lines (Sonnerup 1979)• Higher beta, stronger modulationØerosat+ 2001 NatureSee also Nagai+ 2001 JGRKinetic signatures• Many asymmetric signatures• Few impacts to the global evolution
Bipolar Hall fields

Pritchett 2008

Tanaka+ 2008

Density-gradient-driven (LHD) mode in 3D

Pritchett+ 2011, 2012

Kinetic feedback 1 - diamagnetic suppression• Diamagnetic effect may suppress reconnection (Swisdak+ 2003, 2010)• Derived a criteria• This remains controversial• Unclear theory: diamagnetic flow does not carry magnetic flux
• No confirmation by other groups (i.e., Aunai+ 2013)

Swisdak+ 2003

Observational support
Solar wind

Saturn M’pause

Phan+ 2010The Swisdak criteria:
Earth M’pause

Phan+ 2013

Masters+ 2012

Kinetic feedback 2 - anomalous slow down
B1=1.5

Density

N1 = 1N2 = 3B2 = -0.5
By = 0 or 1

• 64.0 di x 25.6 di, periodic in x, reflecting in zZ• mi : me = 25 : 1YX• Two runs: Coplaner (By=0) vs Guide-field (By ≠ 0)

Coplaner reconnection is slow!!
0.05

Guide-field (By ≠ 0) run

0.04

0.03

0.02

0.01

0020

4060

• Guide-field usually makes RX slow
• Coplaner (By=0) run is anomalously slow
• Consistent with previous work by Pritchett 2008

Coplaner80(By=0) run
Zenitani+ 2010 unpublished
Hesse+ 2013, Aunai+ 2013

Implications-Bz+Bz

Magnetopause

solar wind
dipole fielddF/dtt• Flux/energy/mass transfer by magnetopause reconnection canbe intermittent

Particle confinement?

Hesse+ 2013

• Larger bounce width• Wider current channel ==> Weaker E can drive the current

e-Dissipation region
Nonideal energy dissipation

Field reversal

Zenitani+ 2011

Electron distribution functionZYX• Highly anisotropic, structured
distributionVez• The “half-ring” population is
responsible for the energy
dissipation

VeyLower-origin meandering electrons

Vze

ZtimeXVyeZZXZXYX

Drifting electrons on the upper side

Vze

Z

Vye

timeXZZXZXYXElectron particle picture
e-e-ee-e-• Two current-carrying electrons

Drifting electrons• Meandering electrons(unconfined, dissipative)• drifting electrons(confined, non-dissipative)

Vze• We are still trying to understand• How do they mix each other?
• How to dissipate the energy?

Meandering electrons

VyeSummary• MHD properties– Shock structures– Cassak=Shay=Birn (CSB) model is successful• Kinetic signatures– Bipolar Hall field, density-gradient mode etc.
– Few impacts to global evolution• Major unsolved issues - kinetic effects, related to Δβ– Diamagnetic suppression (Swisdak+ 2003)– Anomalous slow down (Hesse+ 2013)• More simulations needed, using realistic parameters• Next-generation observations will come in 2015