Coronal Loop Expansion Properties Explained Using Separators

TL;DR

This paper investigates why coronal loops maintain a roughly constant thickness along their length, contrasting observations with magnetic reconnection models involving separators.

Contribution

It introduces a Monte Carlo simulation of separator field line expansion to explain the observed uniformity in coronal loop widths.

Findings

Separator field lines can produce nearly constant loop widths.

Magnetic reconnection along separators may explain observed loop properties.

Simulation results align with TRACE and SOHO observations.

Abstract

One puzzling observed property of coronal loops is that they are of roughly constant thickness along their length. Various studies have found no consistent pattern of width variation along the length of loops observed by TRACE and SOHO. This is at odds with expectations of magnetic flux tube expansion properties, which suggests that loops are widest at their tops, and significantly narrower at their footpoints. Coronal loops correspond to areas of the solar corona which have been preferentially heated by some process, so this observed property might be connected to the mechanisms that heat the corona. One means of energy deposition is magnetic reconnection, which occurs along field lines called separators. These field lines begin and end on magnetic null points, and loops forming near them can therefore be relatively wide at their bases. Thus, coronal energization by magnetic reconnection may replicate the puzzling expansion properties observed in coronal loops. We present results of a Monte Carlo survey of separator field line expansion properties, comparing them to the observed properties of coronal loops.