Observations of Non-thermal Velocity and Comparison with Alfv\'en Wave Turbulence Model in Solar Active Regions

TL;DR

This study compares observed non-thermal velocities in solar active regions with Alfvén wave turbulence models, finding good agreement and suggesting recent models can explain observed spectral line widths.

Contribution

It demonstrates that advanced Alfvén wave turbulence models can accurately predict non-thermal velocities observed in solar active regions.

Findings

Observed non-thermal velocities range from 17 to 30 km/s.

Model predictions of 16 interacting flux tubes match observed velocities.

Results support Alfvén wave turbulence as a key mechanism in active region dynamics.

Abstract

We present a study of spectral line width measurements from the Extreme Ultraviolet Imaging Spectrometer (EIS) on {\it Hinode}. We used spectral line profiles of Fe {\sc xvi} 262.984 {\AA}, Fe {\sc xiv} 264.787 {\AA}, Fe {\sc xiv} 270.519 {\AA}, Fe {\sc xiv} 274.203 {\AA}, and Fe {\sc xv} 284.160 {\AA}, and studied 11 active regions. Previous studies of spectral line widths have shown that in hot loops in the cores of active regions, the observed non-thermal velocities are smaller than predicted from models of reconnection jets in the corona or shock heating associated with Alfv\'{e}n waves. The observed line widths are also inconsistent with models of chromospheric evaporation due to coronal nanoflares. We show that recent advances in higher resolution Alfv\'{e}n wave turbulence modeling enables us to obtain non-thermal velocities similar to those measured in active regions. The observed non-thermal velocities for the 11 active regions in our study are in the range of 17$-$30 $\rm km ~ s^{-1}$, consistent with the spectral line non-thermal widths predicted from our model of 16 interacting flux tubes, which are in the range of ~15$-$37 $\rm km ~ s^{-1}$.