The Roles of Reconnected Flux and Overlying Fields in CME Speeds

TL;DR

This study compares how reconnected flux and overlying magnetic field decay influence CME speeds, confirming that both factors are correlated with faster CMEs, with reconnection playing a significant role in acceleration.

Contribution

It provides a comparative analysis of the roles of ribbon fluxes and overlying field decay rates in CME acceleration, highlighting the relative strength of these factors.

Findings

Higher CME speeds correlate with larger ribbon fluxes.

Faster decaying overlying fields are associated with higher CME speeds.

Reconnection likely contributes to CME acceleration through increased hoop force.

Abstract

Researchers have reported (i) correlations of coronal mass ejection (CME) speeds and the total photospheric magnetic flux swept out by flare ribbons in flare-associated eruptive events, and, separately, (ii) correlations of CME speeds and more rapid decay, with height, of magnetic fields in potential coronal models above eruption sites. Here, we compare the roles of both ribbon fluxes and the decay rates of overlying fields in a set of 16 eruptive events. We confirm previous results that higher CME speeds are associated with both larger ribbon fluxes and more rapidly decaying overlying fields. We find the association with ribbon fluxes to be weaker than a previous report, but stronger than the dependence on the decay rate of overlying fields. Since the photospheric ribbon flux is thought to approximate the amount of coronal magnetic flux reconnected during the event, the correlation of speeds with ribbon fluxes suggests that reconnection plays some role in accelerating CMEs. One possibility is that reconnected fields that wrap around the rising ejection produce an increased outward hoop force, thereby increasing CME acceleration. The correlation of CME speeds with more rapidly decaying overlying fields might be caused by greater downward magnetic tension in stronger overlying fields, which could act as a source of drag on rising ejections.