On Sun-to-Earth Propagation of Coronal Mass Ejections: 2. Slow Events and Comparison with Others

TL;DR

This study investigates the propagation characteristics of slow coronal mass ejections from Sun to Earth, comparing them with faster events, and offers insights into their dynamics, interactions, and implications for space weather prediction.

Contribution

It provides a detailed analysis of slow CME propagation phases, compares different CME types, and proposes improved triangulation methods for better Sun-to-Earth kinematic assessments.

Findings

Slow CMEs accelerate gradually up to 20-30 solar radii then maintain near solar wind speed.

Faster CMEs accelerate and decelerate more rapidly with shorter cessation distances.

Slow CMEs often interact with solar wind structures, influencing space weather.

Abstract

As a follow-up study on Sun-to-Earth propagation of fast coronal mass ejections (CMEs), we examine the Sun-to-Earth characteristics of slow CMEs combining heliospheric imaging and in situ observations. Three events of particular interest, the 2010 June 16, 2011 March 25 and 2012 September 25 CMEs, are selected for this study. We compare slow CMEs with fast and intermediate-speed events, and obtain key results complementing the attempt of \citet{liu13} to create a general picture of CME Sun-to-Earth propagation: (1) the Sun-to-Earth propagation of a typical slow CME can be approximately described by two phases, a gradual acceleration out to about 20-30 solar radii, followed by a nearly invariant speed around the average solar wind level, (2) comparison between different types of CMEs indicates that faster CMEs tend to accelerate and decelerate more rapidly and have shorter cessation distances for the acceleration and deceleration, (3) both intermediate-speed and slow CMEs would have a speed comparable to the average solar wind level before reaching 1 AU, (4) slow CMEs have a high potential to interact with other solar wind structures in the Sun-Earth space due to their slow motion, providing critical ingredients to enhance space weather, and (5) the slow CMEs studied here lack strong magnetic fields at the Earth but tend to preserve a flux-rope structure with axis generally perpendicular to the radial direction from the Sun. We also suggest a "best" strategy for the application of a triangulation concept in determining CME Sun-to-Earth kinematics, which helps to clarify confusions about CME geometry assumptions in the triangulation and to improve CME analysis and observations.