1. Solar Atmosphere as a Laboratory for Magnetic Reconnection Shinsuke Imada (ISAS/JAXA)

2. Magnetic Reconnection Current sheet thickness Inflow velocity Outflow velocity Turbulence/wave Ion-Electron Heating Non-thermal acceleration Magnetic field Density Original idea is converting magnetic field energy to plasma kinetic energy. Recently plasma heating, particle acceleration and wave excitation are also well discussed in the category of magnetic reconnection. These energy conversion rates are heavily depending on the plasma conditions. In that sense it is very interesting to discuss magnetic reconnection in various plasma conditions. Slow shock

3. Plasmas in universe Comparative studies important collisionless weak collision collisional This figure shows the density and temperature relationship in the Sun, Earth, Lab, and astro plasmas. The magnetic reconnection is studied in various conditions, from collisionless to collisional regime.

4. What plasma parameter controls? What is the goal of magnetic reconnection study? I already mentioned that the importance of understanding of energy conversion. This figure shows the illustration of the energy conversion in two plasma conditions. In my opinion to answer this puzzles and answer what plasma condition controls the each energy conversion rates.

5. Dynamic activities seen in the chromosphere Many magnetic reconnection seem to be taken place in chromosphere. One of the most important findings by Hinode! I want to mention one of the most important findings by Hinode. Hinode observed very dynamical chromospheric activity which may be associated with magnetic reconnection. Thus now chromosphere is also a target of magnetic reconnection. Is magnetic reconnection the same as coronal reconnection?

6. Relative importance of diffusivities Ambipolar/Hall = ω ci /ν in ω ci : Ion-cyclotron freq ∝ B ν in : Ion-neutral collision freq ∝ n Chromosphere: ambipolar > Hall, resistivity by K.A.P. Singh Assumption: typical magnetic field profile of a vertical flux tube May be not.. Recently Isobe-san studied the magnetic reconnection in chromosphere. He discusses relative importance of magnetic diffusivity between Hall and ambipolar diffusivity in chromosphere, and found ambipolar diffusion is important in chromosphere.

7. x By In the presence of B=0 point Ohmic only Ambipolar diffusion does not work where B=0 Current is concentrated near B=0 => thinning of current sheet This movie shows the current sheet development in case of only ohmic diffusivity. The upper panel shows the magnetic field variation in space, and the bottom is current density. In the case of only ohmic diffusivity, the current will be diffusing.

8. x By In the presence of B=0 point Ambipolar only Ambipolar diffusion does not work where B=0 Current is concentrated near B=0 => thinning of current sheet On the other hand, in the case of ambipolar diffusivity, the magnetic field gradient go steeper and forms the this current sheet. This is because the ambipolar diffusion cannot work magnetic field is zero.

9. 2.5D simulation (still preliminary) Ohmic diffusion only Ohmic+Ambipolar Thin current sheet created by ambipolar diffusion Formation of islands => bursty reconnection Isobe et al, in preparation Thus very bursty/sporadic magnetic reconnection can be taken place in chromosphere.

10. Solar Flare LDE eventImpulsive event Tsuneta et al., 1996 Tsuneta et al., 1997 Let’s move to coronal magnetic reconnection which we have a large amount of knowledge. This is the very famous observation of solar flares, one is LDE and impulsive event. We can see many structure of flare loops, but we cannot see reconnection region itself in many event.

11. Standard model for Solar Flare Yohkoh+Hinode We understand very well We should observe this region! with spectroscopy Tsuneta et al., 1996

12. What we need? Typical dynamical timescale of reconnection 10(Mm)/1000(km/s) ~ 10s To observe steady reconnection, we should take one image within 10 sec Another important point is understanding of Thermal Non-Equilibrium plasma, to understand rapid and strong plasma heating.

13. Thermal Non-Equilibrium Plasma Non-Gaussian Distribution function → Power-law distribution, beam plasma time scale for equilibrium is very short (kinetic regime or e-e or p-p collision) Different temperature in different species → Tp>Te time scale for equilibrium is relatively long (e-p collision) Ionization non-equilibrium → strong heating or flare time scale for equilibrium is relatively long

14. Ion Temperature Imada et al., APJL 2009 Recently Imada et al proposed a method for estimating an ion temperature by using emission lines from different atomic species. This method do not assume Ionization equilibrium. This method will apply to solar flare near future.

15. Ionization Process α collisional and dielectronic recombination S collisional ionization FeXIV FeXV FeXVI ionizationrecombination FeXVII FeXVIII Fe13+ Fe14+ Fe15+ Fe16+ Fe17+ These process linearly depend on density

16. 10^9/cc 1MK Shock angle 85degree Example of ionization calculation 41MK 1200km/s outflow Without thermal conduction T=1MK at t<0 T=41MK t>0

17. Example of ionization calculation in Steady Reconnection model

18. Example of ionization calculation in case of N~10^8/cc

19. Emission measure Black:Jet NEQ 、 Red: Jet EQ 、 Blue:Post flare loop EQ Post Flare loop 20 x 1 Mm 10^11/cc 15MK Ionization EQ

20. Spatial resolution The necessary spatial resolution is the separation of each line peaks. ~1arcsec

21. Necessary for next generation Solar observation To observe the dynamics of magnetic reconnection, we need high throughput spectrometer (This is most important!) We need several emission lines to diagnose inside the reconnection region because of NIEQ (line ratio or filter ratio may not work) To diagnose electron temperature, it is important to observe continuum in X-ray range (photon counting in X-ray range is useful)

22. Spatial resolution needs 0.1~0.5 arcsec Dynamical range is also important to remove the effect of bright post flare loops (Occulter may be useful) If we can change the direction of slit, it is very useful! We want to see this region!

23. 熱伝導有りだと Ti=Te になるのも 電離平衡のタイム スケールとほぼ同 じ Ti ＜ Te になるはず 本当か？？ そもそも本当に SS は等温衝撃波か？ もし SS の加熱がイオ ン電子で異なれば違 いが見られる筈