Resistive jet simulations extending radially self-similar magnetohydrodynamic models

TL;DR

This paper uses resistive MHD simulations to explore how resistivity influences jet dynamics, especially in magnetized outflows, and introduces a new parameter to measure resistive effects in the energy equation.

Contribution

It extends self-similar MHD jet models by incorporating resistivity and introduces a new parameter, $ beta$, to evaluate resistive effects in the energy equation.

Findings

Resistive effects are significant when $ beta extless 1$ in magnetized jets.

Simulations show flows remain close to ideal-MHD solutions for $ beta extgreater 1$.

The new parameter $ beta$ effectively measures resistive influence on jet energetics.

Abstract

Numerical simulations with self-similar initial and boundary conditions provide a link between theoretical and numerical investigations of jet dynamics. We perform axisymmetric resistive magnetohydrodynamic (MHD) simulations for a generalised solution of the Blandford & Payne type, and compare them with the corresponding analytical and numerical ideal-MHD solutions. We disentangle the effects of the numerical and physical diffusivity. The latter could occur in outflows above an accretion disk, being transferred from the underlying disk into the disk corona by MHD turbulence (anomalous turbulent diffusivity), or as a result of ambipolar diffusion in partially ionized flows. We conclude that while the classical magnetic Reynolds number $R_{\rm m}$ measures the importance of resistive effects in the induction equation, a new introduced number, $\rbeta=(\beta/2)R_{\rm m}$ with $\beta$ the plasma beta, measures the importance of the resistive effects in the energy equation. Thus, in magnetised jets with $\beta<2$, when $\rbeta \la 1$ resistive effects are non-negligible and affect mostly the energy equation. The presented simulations indeed show that for a range of magnetic diffusivities corresponding to $\rbeta \ga 1$ the flow remains close to the ideal-MHD self-similar solution.