Magnetic Reconnection resulting from Flux Emergence: Implications for Jet Formation in the lower solar atmosphere?

J. Y. Ding, M. S. Madjarska, J. G. Doyle, Q.M. Lu, K. Vanninathan, and Z. Huang

Fig. 2. Evolution of the magnetic field (solid lines), temperature (colour), and velocity (arrows) at four times for case A1 (a), A2 (b), B1 (c), and B2 (d). The characteristic parameters of magnetic field strength and electron number density are given above each case plot. Note that the colour-coding is different for each run.

Aims We aim at investigating the formation of jet-like features in the lower solar atmosphere, e.g. chromosphere and transition region, as a result of magnetic reconnection.

Methods. Magnetic reconnection as occurring at chromospheric and transition regions densities and triggered by magnetic flux emergence is studied using a 2.5D MHD code. The initial atmosphere is static and isothermal, with a temperature of 2 x 104 K. The initial magnetic field is uniform and vertical. Two physical environments with different magnetic field strength (25 G and 50 G) are presented. In each case, two sub-cases are discussed, where the environments have different initial mass density.

Results. In the case where we have a weaker magnetic field (25 G) and higher plasma density (Ne = 2x 1011 cm−3), valid for the typical quiet Sun chromosphere, a plasma jet would be observed with a temperature of 2–3 x 104 K and a velocity as high as 40 km s−1. The opposite case of a medium with a lower electron density (Ne = 2 x 1010 cm−3), i.e. more typical for the transition region, and a stronger magnetic field of 50 G, up-flows with line-of-sight velocities as high as ∼90 km s−1 and temperatures of 6 × 105 K, i.e. upper transition region – low coronal temperatures, are produced. Only in the latter case, the low corona Fe IX 171 Å shows a response in the jet which is comparable to the O V increase.

Conclusions. The results show that magnetic reconnection can be an efficient mechanism to drive plasma outflows in the chromosphere and transition region. The model can reproduce characteristics, such as temperature and velocity for a range of jet features like a fibril, a spicule, a hot X-ray jet or a transition region jet by changing either the magnetic field strength or the electron density, i.e. where in the atmosphere the reconnection occurs.

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Last Revised: 2011 September 29th