Forward modelling of heating within a coronal arcade

TL;DR

This study uses numerical models and forward modelling to analyze coronal arcade heating, identifying observable signatures such as wave types and magnetic structures, and evaluating the limitations of Doppler velocity measurements.

Contribution

It compares two coronal arcade models driven by different footpoint motions, highlighting how frequency analysis can distinguish heating mechanisms and assessing the accuracy of kinetic energy estimates.

Findings

High-frequency signals indicate short timescale footpoint motions.

Alfvénic and fast wave signatures are identifiable in synthetic data.

Doppler velocities underestimate true kinetic energy due to multiple factors.

Abstract

Aims. We investigate the synthetic observational signatures from numerical models of coronal heating in an arcade to determine what features are associated with such heating, and what tools can be used to identify them. Methods. We consider two simulations of coronal arcades driven by footpoint motions with different characteristic timescales. Forward modelling is then used, and the synthetic emission data is analysed. Results. The total intensity and Doppler velocities clearly show the magnetic structure of the coronal arcade. Contrasts in the local Doppler shift also highlight the locations of separatrix surfaces. The distinguishing feature of the AC and DC models is that of the frequencies. Through FFT analysis of the Doppler velocities, when short timescale footpoint motions are present, higher frequencies are observed. For longer timescale motions, the dominant signal is that of lower frequencies; however, higher frequencies were also detected, which matched the natural Alfv\'en frequency of the background magnetic field. Alfv\'enic wave signatures were identified in both models with fast wave signatures observable in the AC model. Finally, the estimates of the kinetic energy using the Doppler shifts were found to significantly underestimate within these models. Conclusions. Observables identified within this article were from features such as Alfv\'en waves, fast waves, the arcade structure and separatrix surfaces. The two models were differentiated by examining the frequencies present. The Doppler velocities cannot provide accurate estimates of the total kinetic energy or the component parallel to the LOS. This is due to some plasma outside the formation temperature range of the ion, the multi-directional driver, and cancellation of the velocity along the LOS. The impact each factor has on the estimation is dependent on the set up of the model and the chosen emission line.