SolarB science meeting 2003 2 3 5 ISAS

Solar-B science meeting 2003. 2. 3 -5. ISAS, NAOJ Solar Flares and Magnetic Reconnection T. Yokoyama (NAOJ) 1

Introduction • Present status of our understanding (observation, theory) • Open questions on magnetic reconnection theory • (What to be observed) • Warning : very biased ! Carmichael (1964); Sturrock (1966); Hirayama (1974); Kopp & Pneuman (1976) 2

Present status of our understanding — observation • Observational pieces of evidence – Cusps (Tsuneta et al. 1992) – Above-the-loop HXR source (Masuda et al. 1994) – Outflow/ejection (Mc. Kenzie & Hudson 1999; Ohyama & Shibata 1997) – Inflow (Yokoyama et al. 2000) 3

Observational evidence for the magnetic reconnection model 4

Detection of reconnection inflow Yohkoh/SXT SOHO/EIT Yokoyama et al. (2000) 5

Detection of reconnection inflow 6

Present status of our understanding — observation • Observational pieces of evidence – Cusps (Tsuneta et al. 1992) – Above-the-loop HXR source (Masuda et al. 1994) – Outflow/ejection (Mc. Kenzie & Hudson 1999; Ohyama & Shibata 1997) – Inflow (Yokoyama et al. 2000) 7

Present status of our understanding — theory • “Realistic” simulations (e. g. Yokoyama & Shibata 2001) • What is the condition for the fast reconnection ? – The localized resistivity is necessary (Ugai 1992; Kulsrud 2001). 8

“Realistic” simulation of a flare Yokoyama & Shibata (2001) 9

Present status of our understanding — theory • “Realistic” simulations (e. g. Yokoyama & Shibata 2001) • What is the condition for the fast reconnection ? – The localized resistivity is necessary (Ugai 1992; Kulsrud 2001). 10

Localized resistivity for the necessary condition of fast reconnection Yokoyama & Shibata (1994) 11

Present status of our understanding — theory • “Realistic” simulations (e. g. Yokoyama & Shibata 2001) • What is the condition for the fast reconnection ? – The localized resistivity is necessary (Ugai 1992; Kulsrud 2001). 12

Open questions on magnetic reconnection • Local enhancement of magnetic diffusion – Had been a conjecture (Coppi & Friedland 1971) – Finding in laboratory plasma (Ono et al. 2001; Ji et al. 2001) • Scale-matching between the macro and the micro 13

Enhancement of resistivity in the laboratory plasma • Ono et al. (2001) 14

Open questions on magnetic reconnection • Local enhancement of magnetic diffusion – Had been a conjecture (Coppi & Friedland 1971) – Finding in laboratory plasma (Ono et al. 2001; Ji et al. 2001) • Scale-matching between the macro and the micro 15

Enormous gap of scale sizes • Scale-size of the anomalous resistivity d = ri ~ 10 m 　d ; Thickness of the current sheet ri ; Ion Larmor radius • Scale size of a flare: 104 km ! 16

Fractal current sheet • Tajima & Shibata (1997) ~1 km ~104 km ~10 m 17

Turbulence ? in outflow • Tanuma & Shibata (2003) 18

Turbulent reconnection • Lazarian & Vishniac (1999) : large-scale magnetic Mach number of the turbulence 19

MHD simulations of turbulent reconnection • Yokoyama (2003): very preliminary ! 4 Without turbulence pressure Y=0 -4 -32 X=0 32 With turbulence 20

MHD simulations of turbulent reconnection • Yokoyama (2003): very preliminary ! Time 21

Summary • We have many observational pieces of evidence which support the reconnection model of solar flares. • The localized resistivity is necessary for magnetic reconnection, and is now found in the laboratory plasma in the micro-scale. • But there is still an enormous gap between the micro-scale of the anomalous resistivity and the size of a solar flare. • The scale matching problem is very important. The MHD turbulence may be a key process. 22