Chromospheric Jet observed with Hinode & Collisional Reconnection in the Chromosphere : Evidence of Propagating Alfvén Waves and Magnetic Reconnection

○1Naoto Nishizuka, 2Masaki Shimizu, 1Tahei Nakamura, & 1Kazunari Shibata (nisizuka@kwasan.kyoto-u.ac.jp)

1Kwasan and Hida observatories, Kyoto university, 2Department of Mechanical Engineering and Science Graduate

School of Engineering, Kyoto University Ca II H broad band filter images taken with Hinode/SOT

1.Introduction The solar corona is a fully ionized collisionless plasma as well as laboratory and the magnetospherere. Space satellite missions have revealed that magnetic reconnection can release energy rapidly both in the magnetosphere and the solar corona. On the other hand, the solar chromosphere is a weakly ionized collisional plasma, in which we can expect collisional reconnection and reconnection in a plasma with neutral particles. Such a reconnection has never been studied before, so ‘’chromospheric reconnection” is a new field of science. Recent Hinode observations revealed that the solar chromosphere is more dynamic than previously thought. New chromospheric observations with Hinode revealed that jets are ubiquitous in the chromosphere and some of the jets show evidence of magnetic reconnection (Shibata et al. 2007; Katsukawa et al. 2007).

Various chromospheric Jet

(Shibata et al. 2007, Science)

2.Observation & Simulation

Comparison of snapshot jet image between Observation and Simulation

Evidence of propagating Alfvén wave

Simulation model: Basic equations and initial condition

Comparison between Hot / Cool components of the jet and MHD Simulation

3.Summary

◆2D resistive MHD simulation. /Yokoyama & Shibata (1995). ◆plasma β is 4 in the flux sheet , 0.01-0.06 in the corona. ◆CIP-MOCCT scheme, grid points ( 2000 x 1000 ), size 0.2 ◆We assumed anomalous resistivity (Ugai 1985), η=0 for Vd < Vc and η∝( Vd/Vc-1)2 for Vd > Vc : Vd = J/ρ.

MHD simulation results reproduce remarkably well the dynamics and structure of cool and hot jets and their relative timings. We note that both observations and simulations show the generation of Alfven waves when magnetic reconnection occurs: the jet under-goes apparent motion perpendicular to the jet direction at amplitudes of 5-15 km s-1. This velocity is also comparable to that observed for polar X-ray jets (Cirtain et al. 2007). These Alfvén waves are generated by reconnection (Yokoyama 1998; Takeuchi & Shibata 2001), and may contribute to the heating and accelerat-ion of solar wind when the magnetic field is open (Parker 1988; Axford & McKenzie; Suzuki & Inutsuka 2005). Furthermore, a chromospheric jet was well reproduced by our simulation. This may indicate evidence of fast reconnection in the chromosphere, suggesting that not only microscopic but also macroscopic physics are important for reconnection.

Asymmetric reconnection : (Petschek & Thorne 1967) Reconnection occurs between hot plasma and cool plasma. Hot and Cool jets were ejected side by side. Hot jet preceded cool jet.

Energy flux of propagating Alfvén wave : FAlfvén ~1/4πB⊥B||v⊥ ~ρv⊥2vA ~ 8 x 106 erg s-1 cm-2

B||/(4πρ)1/2 ~V|| ~ 200 km s-1, B⊥/B|| ~V⊥/V||~ 0.1, Hence B||~ 20 G, B⊥~2 G

ABSTRACT: Hinode discovered a beautiful giant jet with both cool and hot components at the solar limb on 2007 February 9. Simultaneous observations by the Hinode SOT, XRT, and TRACE 195A satellites revealed that hot (~5 x106 K) and cool (~104 K) jets were located side by side and that the hot jet preceded the associated cool jet (~1–2 min.). A current-sheet-like structure was seen in optical (Ca II H), EUV (195A ), and soft X-ray emissions, suggesting that magnetic reconnection is occurring in the transition region or upper chromosphere. Alfvén waves were also observed with Hinode SOT. These propagated along the jet at velocities of ∼200 km s-1 with amplitudes (transverse velocity) of ~5–15 km s-1 and a period of ~200 s. We performed two-dimensional MHD simulation of the jets on the basis of the emerging flux-reconnection model, by extending Yokoyama and Shibata’s model. We extended the model with a more realistic initial condition (~106 K and 10-7 g cm-3 corona) and compared our model with multiwavelength observations. The improvement of the coronal temperature and density in the simulation model allowed for the first time the reproduction of the structure and evolution of both the cool and hot jets quantitatively, supporting the magnetic reconnection model. The generation and the propagation of Alfvén waves are also reproduced self-consistently in the simulation model. The fact that our simulation explains observations very well may be also evidence of fast reconnection in the chromosphere.

Reconnection rate and Energy release rate: Fast Reconnection occurs in the Chromosphere !?

Fourier spectrum of Alfven wave associated with reconnection [Yokoyama & Shibata 1998]

(Left) Schematic picture of magnetic reconnection. (Right)Time evolution of kinetic and thermal energies of hot/cool jets. Thermal energy is much larger than kinetic energy of hot and cool jets.

Solar chromosphere: Magnetic Reynolds# Rm=LvA/η~106-108 (cf.1014 in the corona) Sweet-Parker: M0~Rm-1/2~10-3-10-4 (Spitzer resistivity) Petchek-type: M0~π/8ln(Rm)~0.03-0.05

Reconnection rate is 0.02-0.1, which means fast reconnection occurs in the collisonal plasma. We should also consider collisions by neutral particles. (Ambipolar Effect)

Physical parameters across a current sheet)

(a-c) Time evolution of a Chromospheric jet observed with Hinode, (d-f) Density distribution of MHD simulation

log Density log Temperature

Vertical distributions of initial parameters

t=91.0

t=95.0

t=98.0

t=102.0

t=106.0 t=106.0

t=102.0

t=98.0

t=95.0

t=91.0