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Dynamical Properties of Solar Current Loops with Line-Tied Footprints: Effects of Toroidal Forces.

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The effects were studied of toroidal forces in current loops embedded in an ambient plasma such as the corona. These forces occur in current carrying plasmas with curvature. The model loop is characterized by twisted magnetic field lines. The magnetic field and current density have toroidal and poloidal components. A current loop was assumed to evolve while maintaining a half-torus configuration. The important geometrical constraint that footpoints are generally immobile on the relevant time scales was not taken into account. In the present paper, the dynamical properties of current loops similar to those of the earlier work are examined with the requirement that the footpoints remain stationary in the photosphere. The behavior of the present, more realistic model is qualitatively similar to that of the earlier model. In particular, the velocities which the apex can achieve under the action of toroidal forces and the magnetic energy released in the form of drag heating are similar in their respective magnitudes. In the present calculation, the ratio eta of the height of the apex and the footpoint separation is a physical parameter. It is found that a low-lying loop small eta can evolve to a taller larger eta loop in a quasi-equilibrium fashion if the current is increased slowly while holding the footpoint separation fixed. Time evolution of the loops and the magnetic energy converted via drag heating are presented. Results are also presented for loops with relatively strong current. It appears that the toroidal forces can lead to a wide range of plasma motion. The accompanying drag heating can take place with a correspondingly wide range of rates. Solar physics. JHD

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  • Astrophysics

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