Estimating the "Dark" Energy Content of the Solar Corona

TL;DR

This paper investigates the true energy content of Alfvenic waves in the solar corona by reconciling different observational measurements, revealing that line-of-sight superposition hides significant wave flux and contributes to non-thermal line broadening.

Contribution

It introduces a simple forward model to resolve measurement discrepancies and provides the first direct evidence linking non-thermal line broadening to hidden wave energy in the corona.

Findings

Line-of-sight superposition explains low observed wave amplitudes.

Strong correlation between line broadening and wave activity.

Reveals large non-thermal linewidths as signatures of hidden energy.

Abstract

The discovery of ubiquitous low-frequency (3-5mHz) Alfvenic waves in the solar chromosphere (with Hinode/SOT), and corona (with CoMP and the Solar Dynamics Observatory, SDO) has provided some insight into the non-thermal energy content of the outer solar atmosphere. However, many questions remain about the true magnitude of the energy flux carried by these waves. Here we explore the apparent discrepancy in the resolved coronal Alfvenic wave amplitude (~0.5km/s) measured by the Coronal Multi-channel Polarimeter (CoMP) compared to those of the Hinode and the SDO near the limb (~20km/s). We use a blend of observational data and a simple forward model of Alfvenic wave propagation to resolve this discrepancy and determine the Alfvenic wave energy content of the corona. Our results indicate that enormous line-of-sight superposition within the coarse spatio-temporal sampling of CoMP hides the strong wave flux observed by Hinode and SDO and leads to the large non-thermal line broadening observed. While this scenario has been assumed in the past, our observations with CoMP of a strong correlation between the non-thermal line broadening with the low amplitude, low frequency Alfvenic waves observed in the corona provide the first direct evidence of a wave-related non-thermal line broadening. By reconciling the diverse measurements of Alfvenic waves we establish large coronal non-thermal linewidths as direct signatures of the hidden, or "dark", energy content in the corona, and provide preliminary constraints on the energy content of the wave motions observed.