Abstract
Aims. We study the emergence of a non-twisted flux tube from the solar interior into the solar atmosphere. We investigate whether the length of the buoyant part of the flux tube (i.e. {\lambda}) affects the emergence of the field and the dynamics of the evolving magnetic flux system. Methods. We perform three-dimensional (3D), time-dependent, resistive, compressible MHD simulations using the Lare3D code. Results. We find that there are considerable differences in the dynamics of the emergence of a magnetic flux tube when {\lambda} is varied. In the solar interior, for larger values of {\lambda}, the rising magnetic field emerges faster and expands more due to its lower magnetic tension. As a result, its field strength decreases and its emergence above the photosphere occurs later than in the smaller {\lambda} case. However, in both cases, the emerging field at the photosphere becomes unstable in two places, forming two magnetic bipoles that interact dynamically during the evolution of the system. Most of the dynamic phenomena occur at the current layer, which is formed at the interface between the interacting bipoles. We find the formation and ejection of plasmoids, the onset of successive jets from the interface, and the impulsive heating of the plasma in the solar atmosphere. We discuss the triggering mechanism of the jets and the atmospheric response to the emergence of magnetic flux in the two cases.
Highlights
Active region formation and dynamic phenomena on the Sun have been associated with magnetic flux emergence from both a theoretical and observational perspective (e.g. Parker 1955; Tsinganos 1980; Priest 1982; Zwaan 1985; Shibata 1999; Archontis et al 2004; Schrijver 2009)
In numerical flux emergence models, a typical initial condition for the subphotospheric magnetic field is a twisted magnetic flux tube, which undergoes a buoyant rise towards the solar surface
We advance the work by Archontis et al (2013) on the emergence of weakly twisted fields by adding two key elements: firstly, we use a non-twisted flux tube and secondly, we study the effect of λ on the overall dynamics of the emerging flux system
Summary
Active region formation and dynamic phenomena on the Sun have been associated with magnetic flux emergence from both a theoretical and observational perspective (e.g. Parker 1955; Tsinganos 1980; Priest 1982; Zwaan 1985; Shibata 1999; Archontis et al 2004; Schrijver 2009). The effect of λ (which affects the curvature of the emerging part of flux tube) on the emergence of weakly twisted flux tubes was studied by Archontis et al (2013) They used similar initial conditions to Murray et al (2006) and Toriumi & Yokoyama (2011) for a flux tube with α = 0.1, but assumed half the length of the buoyant part of the flux tube (λ = 10). In this case, the weakly twisted flux tube did not fail to emerge above the photophere.
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