High-Lundquist Number Scaling in Three-Dimensional Simulations of Parker's Model of Coronal Heating

TL;DR

This study extends 2D simulations of Parker's coronal heating model to 3D, demonstrating that in high-Lundquist number regimes, the heating rate becomes independent of resistivity, with magnetic energy buildup affected by current layer formation.

Contribution

First 3D simulations of Parker's model showing resistivity-independent heating rates at high Lundquist numbers, confirming previous 2D findings and analyzing magnetic energy dependence.

Findings

Heating rate becomes resistivity-independent at high Lundquist numbers.

Magnetic energy buildup is weaker in 3D due to current layer disruption.

Scaling analysis indicates dissipation time influences energy and heating rate.

Abstract

Parker's model is one of the most discussed mechanisms for coronal heating and has generated much debate. We have recently obtained new scaling results in a two-dimensional (2D) version of this problem suggesting that the heating rate becomes independent of resistivity in a statistical steady state [Ng and Bhattacharjee, Astrophys. J., 675, 899 (2008)]. Our numerical work has now been extended to 3D by means of large-scale numerical simulations. Random photospheric footpoint motion is applied for a time much longer than the correlation time of the motion to obtain converged average coronal heating rates. Simulations are done for different values of the Lundquist number to determine scaling. In the high-Lundquist number limit, the coronal heating rate obtained so far is consistent with a trend that is independent of the Lundquist number, as predicted by previous analysis as well as 2D simulations. In the same limit the average magnetic energy built up by the random footpoint motion tends to have a much weaker dependence on the Lundquist number than that in the 2D simulations, due to the formation of strong current layers and subsequent disruption when the equilibrium becomes unstable. We will present scaling analysis showing that when the dissipation time is comparable or larger than the correlation time of the random footpoint motion, the heating rate tends to become independent of Lundquist number, and that the magnetic energy production is also reduced significantly.