The effect of nanoflare flows on EUV spectral lines

TL;DR

This study models how nanoflare-induced plasma flows affect EUV spectral lines, revealing Doppler-shifts and velocities that can inform future solar observations and instrument design.

Contribution

It combines a 2D cellular automaton with the EBTEL model to analyze spectral line effects of nanoflare heating on coronal plasma.

Findings

Doppler-shifts up to tens of km/s at high temperatures

Non-thermal velocities observed in synthetic lines

Complex emission from multi-temperature plasmas influences spectral line profiles

Abstract

The nanoflare model of coronal heating is one of the most successful scenarios to explain, within a single framework, the diverse set of coronal observations available with the present instrument resolutions. The model is based on the idea that the coronal structure is formed by elementary magnetic strands which are tangled and twisted by the displacement of their photospheric footpoints by convective motions. These displacements inject magnetic stress between neighbor strands that promotes current sheet formation, reconnection, plasma heating, and possibly also particle acceleration. Among other features, the model predicts the ubiquitous presence of plasma flows at different temperatures. These flows should, in principle, produce measurable effects on observed spectral lines in the form of Doppler-shifts, line asymmetries and non-thermal broadenings. In this work we use a Two-Dimensional Cellular Automaton Model (2DCAM) developed in previous works, in combination with the Enthalpy Based Thermal Evolution of Loops (EBTEL) model, to analyze the effect of nanoflare heating on a set of known EUV spectral lines. We find that the complex combination of the emission from plasmas at different temperatures, densities and velocities, in simultaneously evolving unresolved strands, produces characteristic properties in the constructed synthetic lines, such as Doppler-shifts and non-thermal velocities up to tens of km s$^{-1}$ for the higher analyzed temperatures. Our results might prove useful to guide future modeling and observations, in particular, regarding the new generation of proposed instruments designed to diagnose plasmas in the 5 to 10 MK temperature range.