Magnetic Structures at the Boundary of the Closed Corona: Interpretation of S-web Arcs

TL;DR

This paper explores the magnetic topology of the Sun's corona, linking the structure of the S-web to magnetic null points, which could influence solar energetic particle and solar wind distribution.

Contribution

It demonstrates the connection between S-web arc features and magnetic null spine lines, offering a new way to identify key heliospheric regions.

Findings

S-web arcs terminate at null spine lines.

Null spine lines map to specific open-closed boundary segments.

Potential to identify regions for solar energetic particles.

Abstract

The topology of magnetic fields near the open-closed flux boundary in the Sun's corona is an important influencing factor in the process of interchange reconnection, whereby plasma is exchanged between open and closed flux domains. Maps of the magnetic squashing factor at the radial outer boundary in coronal field models reveal the presence of the so-called `S-web', and suggest that interchange reconnection could potentially deposit closed coronal material into high-latitude regions far from the heliospheric current sheet. Here we demonstrate that certain features of the S-web reveal the underlying topological structure of the magnetic field. Specifically, in order for the arcing bands of highly squashed magnetic flux of the S-web to terminate or intersect away from the helmet streamer apex, there must be a null spine line that maps a finite segment of the photospheric open-closed boundary up to a singular point in the open flux domain. We propose that this association between null spine lines and arc termination points may be used to identify locations in the heliosphere that are preferential for the appearance of solar energetic particles or slow solar wind plasma with certain characteristics.