Coronal Mass Ejections - Propagation Time and Associated Internal Energy

TL;DR

This study analyzes 91 CME events to understand their propagation times, internal energy, and the effects of solar wind drag and magnetic forces, revealing that most CMEs slow down to match solar wind speeds and dissipate significant internal energy.

Contribution

It provides new insights into CME dynamics by linking propagation times, internal magnetic energy, and the influence of solar wind drag on CME speeds.

Findings

Most CMEs have final speeds less than or equal to their initial speeds.

CME speeds tend to match the background solar wind due to aerodynamic drag.

Effective acceleration indicates energy dissipation of about 10^{31-32} ergs, likely from magnetic forces.

Abstract

In this paper, we analyze 91 coronal mass ejection (CME) events studied by Manoharan et al. (2004) and Gopalswamy and Xie (2008). These earth-directed CMEs are large (width $>$160$^\circ$) and cover a wide range of speeds ($\sim$120--2400 {\kmps}) in the LASCO field of view. This set of events also includes interacting CMEs and some of them take longer time to reach 1 AU than the travel time inferred from their speeds at 1 AU. We study the link between the travel time of the CME to 1 AU (combined with its final speed at the Earth) and the effective acceleration in the Sun-Earth distance. Results indicate that (1) for almost all the events (85 out of 91 events), the speed of the CME at 1 AU is always less than or equal to its initial speed measured at the near-Sun region, (2) the distributions of initial speeds, CME-driven shock and CME speeds at 1 AU clearly show the effects of aero-dynamical drag between the CME and the solar wind and in consequence, the speed of the CME tends to equalize to that of the background solar wind, (3) for a large fraction of CMEs (for $\sim$50% of the events), the inferred effective acceleration along the Sun-Earth line dominates the above drag force. The net acceleration suggests an average dissipation of energy $\sim$10$^{31-32}$ ergs, which is likely provided by the Lorentz force associated with the internal magnetic energy carried by the CME.