Structures of Interplanetary Magnetic Flux Ropes and Comparison with Their Solar Sources

TL;DR

This study compares interplanetary magnetic flux ropes with their solar sources, revealing how magnetic reconnection influences flux rope structure, twist distribution, and helicity, with implications for understanding solar-terrestrial interactions.

Contribution

It systematically analyzes the twist distribution of interplanetary flux ropes and links their properties to solar reconnection processes, providing new insights into flux rope formation and structure.

Findings

Most flux ropes have twist consistent with solar reconnection flux.

Half of the flux ropes have low, uniform twist; others have high twist near the axis.

Flux ropes are not linear force free, showing complex twist profiles.

Abstract

Magnetic reconnection is essential to release the flux rope during its ejection. The question remains: how does the magnetic reconnection change the flux rope structure? Following the original study of \citet{Qiu2007}, we compare properties of ICME/MC flux ropes measured at 1 AU and properties of associated solar progenitors including flares, filaments, and CMEs. In particular, the magnetic field-line twist distribution within interplanetary magnetic flux ropes is systematically derived and examined. Our analysis shows that for most of these events, the amount of twisted flux per AU in MCs is comparable with the total reconnection flux on the Sun, and the sign of the MC helicity is consistent with the sign of helicity of the solar source region judged from the geometry of post-flare loops. Remarkably, we find that about one half of the 18 magnetic flux ropes, most of them being associated with erupting filaments, have a nearly uniform and relatively low twist distribution from the axis to the edge, and the majority of the other flux ropes exhibit very high twist near the axis, of up to $\gtrsim 5$ turns per AU, which decreases toward the edge. The flux ropes are therefore not linear force free. We also conduct detailed case studies showing the contrast of two events with distinct twist distribution in MCs as well as different flare and dimming characteristics in solar source regions, and discuss how reconnection geometry reflected in flare morphology may be related to the structure of the flux rope formed on the Sun.