Abstract
ABSTRACT We study the effect of photospheric footpoint motions on magnetic field structures containing magnetic nulls. The footpoint motions are prescribed on the photospheric boundary as a velocity field that entangles the magnetic field. We investigate the propagation of the injected energy, the conversion of energy, emergence of current layers, and other consequences of the nontrivial magnetic field topology in this situation. These boundary motions lead initially to an increase in magnetic and kinetic energy. Following this, the energy input from the photosphere is partially dissipated and partially transported out of the domain through the Poynting flux. The presence of separatrix layers and magnetic null points fundamentally alters the propagation behavior of disturbances from the photosphere into the corona. Depending on the field-line topology close to the photosphere, the energy is either trapped or free to propagate into the corona.
Highlights
From observations and field extrapolations (e.g., Longcope et al 2003; Platten et al 2014) we know that the solar magnetic field has a rather complex structure
We study the effect of photospheric footpoint motions on magnetic field structures containing magnetic nulls
We investigate the propagation of the injected energy, the conversion of energy, emergence of current layers, and other consequences of the nontrivial magnetic field topology in this situation
Summary
From observations and field extrapolations (e.g., Longcope et al 2003; Platten et al 2014) we know that the solar magnetic field has a rather complex structure. Magnetic field structures exist on much smaller scales, and we know that the lower corona is characterized by a so-called magnetic carpet structure of many short, differently oriented loops due to mixed polarities of opposite signs over a broad range of scales (e.g., Schrijver et al 1998) Such fields contain a large number of magnetic null points with a decreasing population density with height (Longcope et al 2003; Edwards & Parnell 2015). The second approach involves using a much simpler model for the coronal field and plasma, but has the advantage that the detailed time evolution of the coronal field structure and energy distribution may be followed Previous studies of this nature have focused on configurations in which the opposite magnetic polarities on the photosphere are well separated (e.g., Galsgaard et al 2000; Mellor et al 2005; De Moortel & Galsgaard 2006), and have demonstrated that reconnection and plasma heating take place. We conclude with drawing connections to the solar magnetic field
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