1 / 22 Solar Flares and Magnetic Reconnection T. Yokoyama (NAOJ) Solar-B science meeting ISAS, NAOJ

2 / 22 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)

3 / 22 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 (McKenzie & Hudson 1999; Ohyama & Shibata 1997) –Inflow (Yokoyama et al. 2000)

4 / 22 Observational evidence for the magnetic reconnection model

5 / 22 Detection of reconnection inflow SOHO/EIT Yohkoh/SXT Yokoyama et al. (2000)

6 / 22 Detection of reconnection inflow

7 / 22 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 (McKenzie & Hudson 1999; Ohyama & Shibata 1997) –Inflow (Yokoyama et al. 2000)

8 / 22 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).

9 / 22 “Realistic” simulation of a flare Yokoyama & Shibata (2001)

10 / 22 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).

11 / 22 Localized resistivity for the necessary condition of fast reconnection Yokoyama & Shibata (1994)

12 / 22 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).

13 / 22 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

14 / 22 Enhancement of resistivity in the laboratory plasma Ono et al. (2001)

15 / 22 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

16 / 22 Scale-size of the anomalous resistivity  =  i  10 m  i  ; Ion Larmor radius Enormous gap of scale sizes Scale size of a flare: 10 4 km !  ; Thickness of the current sheet

17 / 22 Fractal current sheet Tajima & Shibata (1997) ~10 m ~10 4 km ~1 km

18 / 22 Turbulence ? in outflow Tanuma & Shibata (2003)

19 / 22 Turbulent reconnection Lazarian & Vishniac (1999) : large-scale magnetic Mach number of the turbulence

20 / 22 MHD simulations of turbulent reconnection Yokoyama (2003): very preliminary ! 4 -4 X= Without turbulence With turbulence pressure Y=0

21 / 22 MHD simulations of turbulent reconnection Yokoyama (2003): very preliminary ! Time

22 / 22 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.