Solar Atmosphere as a Laboratory for Magnetic Reconnection

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

2. Magnetic Reconnection Inflow velocity Ion-Electron Heating Non-thermal acceleration Current sheet thickness Outflow velocity Turbulence/wave Slow shock 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.

3. Plasmas in universe weak collision collisionless collisional Comparative studies important 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 Assumption: typical magnetic field profile of a vertical flux tube • Ambipolar/Hall = ωci/νin • ωci : Ion-cyclotron freq ∝B • νin : Ion-neutral collision freq ∝ n by K.A.P. Singh Chromosphere: ambipolar > Hall, resistivity 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. Ohmic only In the presence of B=0 point By x 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. Ambipolar only In the presence of B=0 point By x 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 event Impulsive 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 We should observe this region! with spectroscopy Yohkoh+Hinode We understand very well 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 plasmatime scale for equilibrium is very short (kinetic regime or e-e or p-p collision) • Different temperature in different species→　Tp>Tetime 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 Fe13+ Fe14+ Fe15+ Fe16+ Fe17+ FeXIV FeXV FeXVI FeXVII FeXVIII ionization recombination α collisional and dielectronic recombination S collisional ionization These process linearly depend on density

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

17. Example of ionization calculationin Steady Reconnection model

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

19. Emission measure Post Flare loop 20 x 1 Mm 10^11/cc 15MK Ionization EQ Black:Jet NEQ、Red: Jet EQ、Blue:Post flare loop 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になるはず本当か？？ そもそも本当にSSは等温衝撃波か？ Ti=Teになるのも電離平衡のタイムスケールとほぼ同じ 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