Three-dimensional MHD modeling of propagating disturbances in fan-like coronal loops

TL;DR

This study uses 3D MHD simulations to show that propagating disturbances in coronal loops are primarily slow magnetosonic waves generated by nanoflare-driven upflows, reconciling wave and flow observations.

Contribution

It introduces a broadband velocity driver based on nanoflare energy distribution to model PDs, demonstrating their wave-dominated nature in coronal loops.

Findings

PDs are mainly slow magnetosonic waves.

Upflow pulses excite wave disturbances along loops.

Simulated PDs match observed propagation speeds.

Abstract

Quasi-periodic propagating intensity disturbances (PDs) have been observed in large coronal loops in EUV images over a decade, and are widely accepted to be slow magnetosonic waves. However, spectroscopic observations from Hinode/EIS revealed their association with persistent coronal upflows, making this interpretation debatable. Motivated by the scenario that the coronal upflows could be cumulative result of numerous individual flow pulses generated by sporadic heating events (nanoflares) at the loop base, we construct a velocity driver with repetitive tiny pulses, whose energy frequency distribution follows the flare power-law scaling. We then perform 3D MHD modeling of an idealized bipolar active region by applying this broadband velocity driver at the footpoints of large coronal loops which appear open in the computational domain. Our model successfully reproduces the PDs with similar features as the observed, and shows that any upflow pulses inevitably excite slow magnetosonic wave disturbances propagating along the loop. We find that the generated PDs are dominated by the wave signature as their propagation speeds are consistent with the wave speed in the presence of flows, and the injected flows rapidly decelerate with height. Our simulation results suggest that the observed PDs and associated persistent upflows may be produced by small-scale impulsive heating events (nanoflares) at the loop base, and that the flows and waves may both contribute to the PDs at lower heights.