Geometric and magnetic properties of coronal flux ropes associated with CMEs leading to geomagnetic storms

TL;DR

This study analyzes the magnetic and geometric evolution of three coronal flux ropes associated with CMEs, revealing significant rotation and differences in magnetic field strength from Sun to 1 AU, impacting space weather prediction.

Contribution

It provides new insights into the magnetic field evolution and orientation changes of coronal flux ropes during interplanetary propagation, highlighting challenges in predicting geo-effectiveness.

Findings

Average magnetic field strength at 1 AU is half of near-Sun estimates.

CMEs exhibit over 80-degree rotation during propagation.

Difficulties in predicting final flux-rope orientation for geo-effectiveness.

Abstract

We have studied three Interplanetary Coronal Mass Ejections (ICMEs) having clear signatures of magnetic cloud (MC) arrival at 1 AU and their associated solar sources during 2011 to 2013. Comparing the axial magnetic field strength (B0) of the near-Sun coronal flux-ropes with that of the MC at 1 AU, we have found that the average inferred value of B0 at 1 AU assuming the self-similar expansion of the flux-rope is two times smaller than the value of B0 obtained from the results of MC fitting. Furthermore, by comparing the initial orientation of the flux-rope near the Sun and its final orientation at 1 AU we have found that the three CMEs exhibited more than 80-degree rotation during its propagation through the interplanetary medium. Our study suggests that although the near-Sun magnetic properties of coronal flux-ropes can be used to infer the field strength of the associated MC at 1 AU, it is difficult to estimate the final orientation of the MC axis in order to predict the geo-effectiveness of the ICMEs.