A new view of quiet-Sun topology from Hinode/SOT

TL;DR

This study uses high-resolution Hinode/SOT data to analyze the magnetic topology of the quiet Sun, revealing that most null points are located below the corona, suggesting coronal heating via reconnection at null points is unlikely.

Contribution

It provides a new 3D magnetic field model of the quiet Sun based on high-resolution observations, offering revised null point distributions and implications for coronal heating mechanisms.

Findings

Most null points are below the corona in the photosphere and chromosphere.

Null point density is between 3% and 8% of magnetic fragments.

Coronal heating by null point reconnection is unlikely based on null point distribution.

Abstract

With the recent launch of the Hinode satellite our view of the nature and evolution of quiet-Sun regions has been improved. In light of the new high resolution observations, we revisit the study of the quiet Sun's topological nature. Topology is a tool to explain the complexity of the magnetic field, the occurrence of reconnection processes, and the heating of the corona. This Letter aims to give new insights to these different topics. Using a high-resolution Hinode/SOT observation of the line-of-sight magnetic field on the photosphere, we calculate the three dimensional magnetic field in the region above assuming a potential field. From the 3D field, we determine the existence of null points in the magnetic configuration. From this model of a continuous field, we find that the distribution of null points with height is significantly different from that reported in previous studies. In particular, the null points are mainly located above the bottom boundary layer in the photosphere (54%) and in the chromosphere (44%) with only a few null points in the corona (2%). The density of null points (expressed as the ratio of the number of null points to the number of photospheric magnetic fragments) in the solar atmosphere is estimated to be between 3% and 8% depending on the method used to identify the number of magnetic fragments in the observed photosphere. This study reveals that the heating of the corona by magnetic reconnection at coronal null points is unlikely. Our findings do not rule out the heating of the corona at other topological features. We also report the topological complexity of the chromosphere as strongly suggested by recent observations from Hinode/SOT.