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Probing spectral line asymmetries due to the propagating transverse waves in the solar corona

Ambika Saxena, Vaibhav Pant, Tom Van Doorsselaere, M. Saleem Khan

TL;DR

This work addresses how propagating transverse MHD waves in a density-structured solar corona can imprint spectral line asymmetries. It employs 3D MHD simulations of a polar plume with perpendicular density inhomogeneities and forward models Fe XIII 10749 Å emission to generate synthetic spectra across multiple LOS, analyzed with the BR asymmetry technique. The findings show that transverse waves and uniturbulence produce alternating redward and blueward asymmetries, with amplitudes reaching up to about twenty percent of the peak intensity and secondary peak velocities around 30–40 km s$^{-1}$, propagating with the waves and detectable by DKIST. These results suggest spectral line asymmetries as a diagnostic for identifying transverse wave–induced uniturbulence and, more broadly, for tracing mass and energy transport in the corona.

Abstract

Decades-long studies of asymmetric spectral lines in the solar corona suggest mass and energy transport from lower atmospheric layers to the corona. While slow magnetoacoustic waves and plasma flows are recognized as drivers of these spectral line asymmetries, the role of transverse MHD waves remains largely unexplored. Previous simulations have shown that unidirectionally propagating kink waves, in the presence of perpendicular density inhomogeneities, can produce a turbulence-like phenomenon called ``uniturbulence''. However, the spectroscopic signatures of this effect have not been investigated until now. Due to varying Doppler shifts from the plasma elements with different emissions, we expect to observe signatures of both blueward and redward asymmetries. Past instruments like EIS may have missed these signatures due to resolution limitations, but current instruments like DKIST offer a better opportunity for detection. We conducted 3D MHD simulations of transverse waves in a polar plume with density inhomogeneities and performed forward modeling for the Fe XIII emission line at 10749 Å. Our findings show that transverse waves and uniturbulence induce alternating red and blueward asymmetries, with magnitudes reaching up to 20\% of peak intensity and secondary peak velocities between 30 and 40 km s$^{-1}$, remaining under 100 km s$^{-1}$. These asymmetries propagate with the transverse waves, and even at DKIST resolution, similar signatures can be detected. Our study suggests that spectral line asymmetries can serve as a diagnostic tool for detecting transverse wave-induced uniturbulence.

Probing spectral line asymmetries due to the propagating transverse waves in the solar corona

TL;DR

This work addresses how propagating transverse MHD waves in a density-structured solar corona can imprint spectral line asymmetries. It employs 3D MHD simulations of a polar plume with perpendicular density inhomogeneities and forward models Fe XIII 10749 Å emission to generate synthetic spectra across multiple LOS, analyzed with the BR asymmetry technique. The findings show that transverse waves and uniturbulence produce alternating redward and blueward asymmetries, with amplitudes reaching up to about twenty percent of the peak intensity and secondary peak velocities around 30–40 km s, propagating with the waves and detectable by DKIST. These results suggest spectral line asymmetries as a diagnostic for identifying transverse wave–induced uniturbulence and, more broadly, for tracing mass and energy transport in the corona.

Abstract

Decades-long studies of asymmetric spectral lines in the solar corona suggest mass and energy transport from lower atmospheric layers to the corona. While slow magnetoacoustic waves and plasma flows are recognized as drivers of these spectral line asymmetries, the role of transverse MHD waves remains largely unexplored. Previous simulations have shown that unidirectionally propagating kink waves, in the presence of perpendicular density inhomogeneities, can produce a turbulence-like phenomenon called ``uniturbulence''. However, the spectroscopic signatures of this effect have not been investigated until now. Due to varying Doppler shifts from the plasma elements with different emissions, we expect to observe signatures of both blueward and redward asymmetries. Past instruments like EIS may have missed these signatures due to resolution limitations, but current instruments like DKIST offer a better opportunity for detection. We conducted 3D MHD simulations of transverse waves in a polar plume with density inhomogeneities and performed forward modeling for the Fe XIII emission line at 10749 Å. Our findings show that transverse waves and uniturbulence induce alternating red and blueward asymmetries, with magnitudes reaching up to 20\% of peak intensity and secondary peak velocities between 30 and 40 km s, remaining under 100 km s. These asymmetries propagate with the transverse waves, and even at DKIST resolution, similar signatures can be detected. Our study suggests that spectral line asymmetries can serve as a diagnostic tool for detecting transverse wave-induced uniturbulence.

Paper Structure

This paper contains 6 sections, 10 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Simulated and Forward Modeled Data
  3. Data Analysis and Results
  4. The BR Asymmetry Technique
  5. Spectral line asymmetry for a single LOS
  6. Variation of the spectral line asymmetry with height and time

Figures (3)

  • Figure 1: Full simulation cube at $t = 0$. The $x-$ axis represents the radial direction. The density stratification is evident along the radial direction, while density inhomogeneities can be seen in the $y-z$ plane Pant2019InvestigatingE.
  • Figure 2: Spatial maps of BR asymmetry, ${(\frac{B-R}{I})_m}$ values, for LOS integrated emission along $z$-axis, for a) $t$ = 200 s, b) 400 s, c) 720 s, and d) 920 s of the simulation, where the velocity driver has speed, $v_{rms}$ = 15 km s$^{-1}$.
  • Figure 3: Distance--time maps for the BR asymmetry features for $v_{\mathrm{rms}} = 15~\mathrm{km~s^{-1}}$: (a) The slit position is depicted by the dashed line on the BR asymmetry map, and (b) the distance--time map of the features along the slit length shown in (a). The black solid lines depict the slopes of the propagating BR asymmetry features.