Study of the three-dimensional shape and dynamics of coronal loops observed by Hinode/EIS

TL;DR

This study analyzes the 3D shape and plasma flows of coronal loops in an active region using Hinode/EIS data, revealing complex flow patterns and magnetic structures with consistent twist directions.

Contribution

It introduces a method to reconstruct 3D loop shapes and plasma flows from spectral data, and compares these with magnetic extrapolations to understand coronal loop dynamics.

Findings

Most loops show unidirectional flows from footpoints.

Loops exhibit different flow patterns in different spectral lines.

Magnetic extrapolations reveal left-handed twist consistent with the active region.

Abstract

We study plasma flows along selected coronal loops in NOAA Active Region 10926, observed on 3 December 2006 with Hinode's EUV Imaging Spectrograph (EIS). From the shape of the loops traced on intensity images and the Doppler shifts measured along their length we compute their three-dimensional (3D) shape and plasma flow velocity using a simple geometrical model. This calculation was performed for loops visible in the Fe VIII 185 Ang., Fe X 184 Ang., Fe XII 195 Ang., Fe XIII 202 Ang., and Fe XV 284 Ang. spectral lines. In most cases the flow is unidirectional from one footpoint to the other but there are also cases of draining motions from the top of the loops to their footpoints. Our results indicate that the same loop may show different flow patterns when observed in different spectral lines, suggesting a dynamically complex rather than a monolithic structure. We have also carried out magnetic extrapolations in the linear force-free field approximation using SOHO/MDI magnetograms, aiming toward a first-order identification of extrapolated magnetic field lines corresponding to the reconstructed loops. In all cases, the best-fit extrapolated lines exhibit left-handed twist (alpha < 0), in agreement with the dominant twist of the region.