Magnetic Reconnectionin Large and Fully Kinetic System
Keizo Fujimoto1,2, Takahiro Obara2
1. University of Alberta, Edmonton, Alberta, CANADA
2. NiCT, Koganei, Tokyo, JAPANfujimoto@phys.ualberta.ca

Introduction
Important phenomena relating with space weather forecasting[Solar flares][Magnetospheric substorm](http://vestige.lmsal.com/TRACE/)
CAWSES International Workshop on
Space Weather Modeling(http://www2.
nict.go.jp/dk/c232/)

Introduction
Main issues on magnetic reconnection in solar flares andmagnetospheric substorm
1.

What is the mechanism to quickly initiate reconnection?
When and where can reconnection be triggered in thesystems of interest?

2.

What is the mechanism to support a quasi-steady fast reconnection?
Is it possible to explain the energy release associated withsolar flares and magnetospheric substorm by reconnection
alone?

3.

How and where can plasmas be accelerated and heated?
What is the energy transport processes associated withreconnection?
CAWSES International Workshop on
Space Weather ModelingIntroduction
What is the fast reconnection?
Fast reconnection: Ey〜0.1 VA0B0(VA0, B0: Alfven velocity and magnetic field in the lobes.)¾ Within 10 minutes, about 15 Re of magnetic flux in lobes can bereconnected in the Earth magnetotail.
¾ Within 50 seconds, most of the magnetic field in the flux tube with an area
1018 cm2 and a length 109 cm can be reconnected in the solar flares.

CAWSES International Workshop on
Space Weather ModelingIntroduction
Quasi-steady models of fast reconnection
9 MHD model:[Petschek, 1964]

9 Kinetic model （GEM Reconnection Challenge, 2001）：
Inside the electron diffusion region

Outside the electron diffusion region

Due to periodic
boundaries

Inclusion of the Hall term is sufficientcondition for fast reconnection. [e.g.,Birn et al., 2001][Hesse et al., 2001]

However, steady-state reconnection is not achieved.
CAWSES International Workshop on
Space Weather ModelingEM code with adaptive mesh refinement (AMR) technique
AMR techniqueParticle splitting algorithm∆r = ∆L/N1/2

N: Number of particles in the cell.

x1,2 = x0 ± ∆r; x3,4 = x0
y1,2 = y0; y3,4 = y0 ± ∆r
V1,2,3,4 = V0;
q1,2,3,4 = q0/4;
m1,2,3,4 = m0/4

CAWSES International Workshop on
Space Weather ModelingTime evolution of the reconnection rate

CAWSES International Workshop on
Space Weather ModelingWhy do the reconnection rate decrease?

CAWSES International Workshop on
Space Weather Modeling

How can the electron diffusion region be elongated?

[Fujimoto, Phys. Plasmas, 2006]

mi/me=1
mi/me=100

Curvatureof field line
Electron current
CAWSES International Workshop on
Space Weather Modeling

Comparison with observations(Simulation result)
Consistent with observations. （e.g., Asano et al., 2004）

Expected mechanism to enhance Ey
Buneman-type instability
can be excited.

Electronpressure tensor

Electron Anomalousinertia
resistivity
CAWSES International Workshop onSpace Weather ModelingSummary and Conclusions
We have investigated the time evolution of magnetic reconnection in large
and fully kinetic systems. Our kinetic code employs the AMR and particle
splitting techniques.
1. Inclusion of the Hall term is NOT sufficient for quasi-steady fastreconnection.
The polarization field, which is caused by the inertia difference
between ions and electrons, elongates the electron diffusion region,
so that quasi-steady reconnection is not achieved.
2. Inclusion of the Hall term is NOT necessarily required for fast reconnection.
Even in the system without the Hall effects (mi/me = 1), fast reconnection
can occur.

CAWSES International Workshop on
Space Weather ModelingSummary and Conclusions
Buneman-type instability is expected to give an anomalous resistivity,
enhancing the reconnection rate. However, it is not clear how much itaffects the system.

We need to extend the present 2-D code to the 3-D code and investigate theeffects of the anomalous resistivity on magnetic reconnection.

CAWSES International Workshop on
Space Weather Modeling