Upflows in the upper transition region of the quiet Sun

TL;DR

This study examines the nature of upflows in the upper transition region of the quiet Sun, revealing that they are associated with closed magnetic loops rather than open fields, indicating mass supply to coronal loops.

Contribution

It combines magnetic field extrapolations with EUV spectroscopy to clarify the origin of Ne VIII blue shifts in quiet Sun regions, challenging previous assumptions about solar wind sources.

Findings

Upflows are linked to closed magnetic loops, not open fields.

Significant upflows occur in both legs of funnel-shaped loops.

Upflows in the upper TR are often not cospatial with downflows in the middle TR.

Abstract

We investigate the physical meaning of the prominent blue shifts of Ne VIII, which is observed to be associated with quiet-Sun network junctions (boundary intersections), through data analyses combining force-free-field extrapolations with EUV spectroscopic observations. For a middle-latitude region, we reconstruct the magnetic funnel structure in a sub-region showing faint emission in EIT-Fe 195. This funnel appears to consist of several smaller funnels that originate from network lanes, expand with height and finally merge into a single wide open-field region. However, the large blue shifts of Ne VIII are generally not associated with open fields, but seem to be associated with the legs of closed magnetic loops. Moreover, in most cases significant upflows are found in both of the funnel-shaped loop legs. These quasi-steady upflows are regarded as signatures of mass supply to the coronal loops rather than the solar wind. Our observational result also reveals that in many cases the upflows in the upper transition region (TR) and the downflows in the middle TR are not fully cospatial. Based on these new observational results, we suggest different TR structures in coronal holes and in the quiet Sun.