The spheromak tilting and how it affects modelling coronal mass ejections

TL;DR

This study investigates how the tilting and rotation of spheromak flux ropes, used in CME modeling, affect magnetic topology predictions, emphasizing the importance of initial conditions and ambient field interactions.

Contribution

It reveals the impact of spheromak tilt and rotation during insertion on space weather modeling accuracy, a previously underexplored aspect.

Findings

Spheromaks rotate to align with ambient magnetic fields.

Rotation angle depends on initial tilt, speed, and ambient field strength.

Rotation occurs under various initial conditions and magnetic configurations.

Abstract

Spheromak type flux ropes are increasingly used for modelling coronal mass ejections (CMEs). Many models aim in accurately reconstructing the magnetic field topology of CMEs, considering its importance in assessing their impact on modern technology and human activities in space and on ground. However, so far there is little discussion about how the details of the magnetic structure of a spheromak affect its evolution through the ambient field in the modelling domain, and what impact this has on the accuracy of magnetic field topology predictions. If the spheromak has its axis of symmetry (geometric axis) at an angle with respect to the direction of the ambient field, then the spheromak starts rotating so that its symmetry axis finally aligns with the ambient field. When using the spheromak in space weather forecasting models this tilting can happen already during insertion and significantly affects the results. In this paper we highlight this issue previously not examined in the field of space weather and we estimate the angle by which the spheromak rotates under different conditions. To do this we generated simple purely radial ambient magnetic field topologies (weak/strong positive/negative) and inserted spheromaks with varying initial speed and tilt, and magnetic helicity sign. We employ different physical and geometric criteria to locate the magnetic centre of mass and axis of symmetry of the spheromak. We confirm that spheromaks rotate in all investigated conditions and their direction and angle of rotation depend on the spheromak's initial properties and ambient magnetic field strength and orientation.