Effect of transport coefficients on excitation of flare-induced standing slow-mode waves in coronal loops

TL;DR

This study uses 1D nonlinear MHD simulations to validate how altered transport coefficients, especially enhanced viscosity, influence the rapid formation and damping of standing slow-mode waves in flaring coronal loops, aligning with recent observations.

Contribution

It demonstrates that seismology-derived transport coefficients significantly affect wave excitation and damping, providing a better match to observations than classical coefficients.

Findings

Enhanced viscosity accelerates standing wave formation.

Damping time scales quadratically with wave period in the modified model.

Classical coefficients result in slower wave formation and linear damping scaling.

Abstract

Standing slow-mode waves have been recently observed in flaring loops by the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO). By means of the coronal seismology technique transport coefficients in hot ($\sim$10 MK) plasma were determined by Wang et al.(2015, Paper I), revealing that thermal conductivity is nearly suppressed and compressive viscosity is enhanced by more than an order of magnitude. In this study we use 1D nonlinear MHD simulations to validate the predicted results from the linear theory and investigate the standing slow-mode wave excitation mechanism. We first explore the wave trigger based on the magnetic field extrapolation and flare emission features. Using a flow pulse driven at one footpoint we simulate the wave excitation in two types of loop models: model 1 with the classical transport coefficients and model 2 with the seismology-determined transport coefficients. We find that model 2 can form the standing wave pattern (within about one period) from initial propagating disturbances much faster than model 1, in better agreement with the observations. Simulations of the harmonic waves and the Fourier decomposition analysis show that the scaling law between damping time ($\tau$) and wave period ($P$) follows $\tau\propto{P^2}$ in model 2, while $\tau\propto{P}$ in model 1. This indicates that the largely enhanced viscosity efficiently increases the dissipation of higher harmonic components, favoring the quick formation of the fundamental standing mode. Our study suggests that observational constraints on the transport coefficients are important in understanding both, the wave excitation and damping mechanisms.