Solar Cycle Variation of Magnetic Flux Ropes in a Quasi-Static Coronal Evolution Model

TL;DR

This study models the solar corona's magnetic flux ropes over the solar cycle, revealing how their number and ejections vary with activity, and compares predictions with observed coronal mass ejection patterns.

Contribution

It introduces a non-potential, time-dependent coronal magnetic field model that captures flux rope evolution and cycle variation, improving understanding of solar activity effects.

Findings

Flux rope count doubles from solar minimum to maximum.

Flux rope ejections increase eightfold over the cycle.

Model predicts persistent sheared magnetic structures at all latitudes.

Abstract

The structure of electric current and magnetic helicity in the solar corona is closely linked to solar activity over the 11-year cycle, yet is poorly understood. As an alternative to traditional current-free "potential field" extrapolations, we investigate a model for the global coronal magnetic field which is non-potential and time-dependent, following the build-up and transport of magnetic helicity due to flux emergence and large-scale photospheric motions. This helicity concentrates into twisted magnetic flux ropes, which may lose equilibrium and be ejected. Here, we consider how the magnetic structure predicted by this model-in particular the flux ropes-varies over the solar activity cycle, based on photospheric input data from six periods of cycle 23. The number of flux ropes doubles from minimum to maximum, following the total length of photospheric polarity inversion lines. However, the number of flux rope ejections increases by a factor of eight, following the emergence rate of active regions. This is broadly consistent with the observed cycle modulation of coronal mass ejections, although the actual rate of ejections in the simulation is about a fifth of the rate of observed events. The model predicts that, even at minimum, differential rotation will produce sheared, non-potential, magnetic structure at all latitudes.