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速報 “ Fast Magnetic Reconnection via Jets and Current Microsheets”. by P. G. Watson & I. J. D. Craig 2003, ApJ, 590, L0000(in press). Abstract. Numerical simulations of highly nonlinear magnetic reconnection provide evidence of ultrathin current microsheets. - PowerPoint PPT Presentation
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速報“ Fast Magnetic Reconnection via J
ets and Current Microsheets”
by P. G. Watson & I. J. D. Craig
2003, ApJ, 590, L0000(in press)
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.
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.
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
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.
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)
Craig & Henton 1995
Hirose, Litvinenko, Shibata, Tanuma et al. (in prep.)
The Reconnection Simulations
• Initial condition:
• Including resistivity and viscousity
• Simulation region: -1<x,y<1
/)cos(
/)sin()sin(
ˆ),,(
ˆ),,(
x
yx
ztyxB
ztyxv
Initial Condition
Prim
ary current sheet
Results
Secondary current sheet
Jet
Jet
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)
Results(V and B)
Results(Current)
Primary sheet
Secondary sheet
Results(J v.s. Time)
Secondary sheet
Primary sheet
Dependence of Results on Resistivity
fast
slowfast
Much thinner than primary one
Discussion and Conclusions• Secondary (small-scale) current sheet is created by t
he 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).