Slow and sausage loop mode excitation due to local and global spontaneous perturbations

TL;DR

This study investigates how local and global energy perturbations in solar flaring loops excite slow and sausage magnetohydrodynamic modes, revealing that local microflare energies induce slow shocks while global heating triggers sausage modes.

Contribution

It demonstrates that local microflare energy depositions consistently excite slow modes, whereas global perturbations are necessary for observable sausage mode excitation, highlighting the importance of perturbation scale.

Findings

Local microflare energies induce slow shock waves and slow modes.

Global perturbations are required to excite sausage modes.

Sausage mode excitation depends on the nature of the energy source, not on plasma beta.

Abstract

We analyse the capability of different type of perturbations -associated with usual environment energy fluctuations of the solar corona- to excite slow and sausage modes in solar flaring loops. We perform numerical simulations of the MHD ideal equations considering straight plasma magnetic tubes subject to local and global energy depositions. We find that local loop energy depositions of typical microflares [$\sim$($10^{27}$-$10^{30}$) erg] are prone to drive slow shock waves that induce slow mode patterns. The slow mode features are obtained for every tested local energy deposition inside the loop. Meanwhile, to obtain an observable sausage mode pattern a global perturbation, capable to modify instantaneously the internal loop temperature, is required, i.e. the characteristic conductive heating time must be much smaller than the radiative cooling one. Experiments carried out by varying parameter $\beta$ show us that the excitation of sausage modes does not depend significantly on the value of this parameter but on the global or local character of the energy source.