1. 速報 “Fast Magnetic Reconnection via Jets and Current Microsheets”
by P. G. Watson & I. J. D. Craig
2003, ApJ, 590, L0000(in press)

2. Abstract
Numerical simulations of highly nonlinear magnetic reconnection provide evidence of ultrathin current microsheets.
These small-scale sheets are formed by strong jets from a primary large-scale current layer.
The size of the secondary microsheet is determined by the resistivity.
This scaling suggests that microsheets may provide fast reconnection sites in the solar corona.

3. Introduction(1/3)
Fast reconnection occurs in solar corona, in which the reconnection rate is independent of resistivity.
The purpose of the letter is to point out that the exhaust region of a large-scale current layer can provide the external source for small-scale secondary reconnection events.

4. Introduction(2/3)
Numerical simulations show that ejecta from the primary sheet act rather like a turbo mechanism, enhancing dissipation by supplying high-pressure collimated jets to sustain the microsheet.
Shibata et al. 1994

5. Introduction(3/3)
The microsheet is very much smaller than primary sheet, its length being controlled by the narrow exhaust jet of the primary current layer.
Such microsheets have the potential to act as extremely short-lived localized sites of energy release (e.g., X-ray bright points) in magnetically complex plasmas such as the solar corona.

6. Reconnection Model Simulations: Heerikhuisen, Craig & Watson(2000),
Watson & Craig(2001),
　Hirose, Litvinenko, Shibata, Tanuma et al.(in prep.)
Analytic models:
Craig & Henton(1995),
Craig & Fabling (1996),
Craig & Watson(2000)

7. Craig & Henton 1995
Hirose, Litvinenko, Shibata, Tanuma et al. (in prep.)

8. The Reconnection Simulations
Initial condition:
Including resistivity and viscousity
Simulation region: -1<x,y<1

9. Initial Condition
Primary current sheet

10. Results
Jet
Secondary current sheet
Jet

11. Results
Primary sheet: Fast reconnection  Saturation of sheet  Sweet-Parker
Secondary sheet: Fast reconnection
Typical model α=1, ε=0.3
(Resistivity is uniform: eta=ν=0.0001)

12. Results(V and B)

13. Results(Current)
Secondary sheet
Primary sheet

14. Results(J v.s. Time)
Secondary sheet
Primary sheet

15. Dependence of Results on Resistivity
slow
fast
fast
Much thinner than
primary one

16. Discussion and Conclusions
Secondary (small-scale) current sheet is created by the collision between two reconnection jets.
Fast reconnection can occurs in the secondary sheet even after the fast reconnection stops in the primary one.
Although the bulk of energy release probably occurs in the primary structure, microsheets powered by primary ejecta could well account for localized hot spots within the plasma(e.g., X-ray-bright points associated with solar flares).