Magnetic reconnection resulting from flux emergence: implications for jet formation in the lower solar atmosphere?

Abstract

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 × 10 4 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 (N e = 2 × 10 11 cm −3 ), valid for the typical quiet Sun chromosphere, a plasma jet would be observed with a temperature of 2-3 × 10 4 K and a velocity as high as 40 km s −1 . The opposite case of a medium with a lower electron density (N e = 2 × 10 10 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 × 10 5 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.

Generation of solar spicules and subsequent atmospheric heating

“…Our results support the hypothesis that fast spicules originate from magnetic reconnection (14,20,21). It is possible that a sub-photospheric local dynamo mechanism (22) or magnetoconvection process (13,23) generates weak magnetic fields close to the large-scale network fields.…”

“…Theoretical models of spicules have included driving by shock waves (2,3), AlfvŽn waves (11,12), amplified magnetic tension (13), or magnetic reconnection (14). However, observations of their formation process are limited, due to insufficient resolution and sensitivity.…”

Heating Mechanisms in the Low Solar Atmosphere Through Magnetic Reconnection in Current Sheets

“…Most of the previous numerical simulations which focus on the formations of EBs (e.g., Chen et al 2001;Isobe et al 2007;Archontis & Hood 2009), chromosphere jets (e.g., Ding et al 2010Ding et al , 2011Yang et al 2013) and micro-flares (e.g., Jiang et al 2012;Archontis & Hansteen 2014) are studied based on the single fluid MHD equations with an assumed anomalous resistivity. The topology structures and many characteristics in these numerical simulations can match well with the observation results.…”

Physical conditions in the chromosphere of a two-ribbon solar flare accompanied by a surge: 1

“…The results of numerical simulation of ejections caused by the outflow of a new magnetic flux prove that the magnetic reconnections in the solar lower atmosphere, including the chromosphere, are an effec tive mechanism generating the plasma motion in the chromosphere and transition layer that is observed in the ejections [10,15,21].…”