Signature of mass supply to quiet coronal loops

TL;DR

This study investigates the origin of large Ne viii blue shifts in the quiet Sun, revealing that they are more indicative of mass supply to coronal loops rather than solar wind from coronal funnels.

Contribution

It demonstrates for the first time that coronal funnels exist in the quiet Sun and clarifies that large Ne viii blue shifts are linked to mass supply to loops, not necessarily to the solar wind.

Findings

Coronal funnels are present in the quiet Sun.

Large Ne viii blue shifts are not always associated with funnels.

Mass supply rate to coronal loops is estimated at about 10^34 s^-1.

Abstract

Aims. The physical implication of large blue shift of Ne viii in the quiet Sun region is investigated in this paper. Methods. We compare the significant Ne viii blue shifts, which are visible as large blue patches on the Doppler-shift map of a middlelatitude quiet-Sun region observed by SUMER, with the coronal magnetic-field structures as reconstructed from a simultaneous photospheric magnetogram by means of a force-free-field extrapolation. Results. We show for the first time that coronal funnels also exist in the quiet Sun. The region studied contains several small 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 the Ne viii line are not generally associated with funnels. A comparison between the projections of coronal loops onto the solar x-y-plane and the Ne viii dopplergram indicates that there are some loops that reveal large Ne viii blue shifts in both legs, and some loops with upflow in one and downflow in the other leg. Conclusions. Our results suggest that strong plasma outflow, which can be traced by large Ne viii blue shift, is not necessarily associated with the solar wind originating in coronal funnels but appears to be a signature of mass supply to coronal loops. Under the assumption that the measured Doppler shift of the Ne viii line represents the real outflow velocity of the neon ions being markers of the proton flow, we estimate the mass supply rate to coronal loops to be about 10\^{34} s\^{-1}.