# Investigating `dark' energy in the solar corona using forward modeling of MHD waves

## TL;DR

This study uses 3D MHD simulations to demonstrate that the apparent energy discrepancy in solar coronal Alfvénic waves is due to line-of-sight superposition effects, revealing that the true wave energy is hidden in non-thermal line widths.

## Contribution

The paper provides the first comprehensive simulation-based evidence that line-of-sight superposition accounts for the observed energy discrepancy, eliminating the need for additional 'dark' energy sources.

## Key findings

- LOS superposition reduces Doppler velocities and increases non-thermal line widths.
- Simulated correlation matches observed wedge-shaped pattern.
- True wave energy is 0.2-1% of observed energy, explaining the discrepancy.

## Abstract

It is now well established that the Alfv\'enic waves are ubiquitous in the solar corona. However, the Alfv\'enic wave energy estimated from the Doppler velocity measurements in the corona was found to be four orders of magnitude less than that estimated from non-thermal line widths. McIntosh & De Pontieu (2012) suggested that this discrepancy in energy might be due to the line-of-sight (LOS) superposition of the several oscillating structures, which can lead to an underestimation of the Alfv\'enic wave amplitudes and energies. McIntosh & De Pontieu (2012) termed this coronal `dark' or `hidden' energy. However, their simulations required the use of an additional, unknown source of Alfv\'enic wave energy to provide agreement with measurements of the coronal non-thermal line widths. In this study, we investigate the requirement of this unknown source of additional `dark' energy in the solar corona using gravitationally stratified 3D magnetohydrodynamic (MHD) simulations of propagating waves. We excite the transverse MHD waves and generate synthetic observations for the Fe XIII emission line. We establish that the LOS superposition greatly reduces the Doppler velocity amplitudes and increases the non-thermal line widths. Importantly, our model generates the observed wedge-shaped correlation between Doppler velocities and non-thermal line widths. We find that the observed wave energy is only 0.2-1\% of the true wave energy which explains 2-3 orders of magnitude of the energy discrepancy. We conclusively establish that the true wave energies are hidden in the non-thermal line widths. Hence, our results rule out the requirement for an additional `dark' energy in the solar corona.