Coronal Magnetic Structure of Earthbound CMEs and In situ Comparison

TL;DR

This study compares the intrinsic flux rope type of CMEs with in situ measurements at Earth, revealing that CME evolution significantly affects magnetic structure predictions crucial for space weather forecasting.

Contribution

It introduces a method to estimate intrinsic CME flux rope types using indirect proxies and quantifies the mismatch between predicted and observed magnetic structures.

Findings

Only 20% of CME events match strictly between intrinsic and in situ flux rope types.

Match percentage increases to 55% when considering intermediate orientations.

Most CMEs undergo significant rotation, with 35% changing by more than 90 degrees.

Abstract

Predicting the magnetic field within an Earth-directed coronal mass ejection (CME) well before its arrival at Earth is one of the most important issues in space weather research. In this article, we compare the intrinsic flux rope type, i.e. the CME orientation and handedness during eruption, with the in situ flux rope type for 20 CME events that have been uniquely linked from Sun to Earth through heliospheric imaging. Our study shows that the intrinsic flux rope type can be estimated for CMEs originating from different source regions using a combination of indirect proxies. We find that only 20% of the events studied match strictly between the intrinsic and in situ flux rope types. The percentage rises to 55% when intermediate cases (where the orientation at the Sun and/or in situ is close to 45{\deg}) are considered as a match. We also determine the change in the flux rope tilt angle between the Sun and Earth. For the majority of the cases, the rotation is several tens of degrees, whilst 35% of the events change by more than 90{\deg}. While occasionally the intrinsic flux rope type is a good proxy for the magnetic structure impacting Earth, our study highlights the importance of capturing the CME evolution for space weather forecasting purposes. Moreover, we emphasize that determination of the intrinsic flux rope type is a crucial input for CME forecasting models.