Can solar wind viscous drag account for CME deceleration?

TL;DR

This paper develops a physical model for the aerodynamic drag on CMEs based on solar wind viscosity, providing a more realistic understanding of CME deceleration that aligns well with observations.

Contribution

It introduces the first physically derived viscosity-based model for CME drag coefficient, improving the understanding of CME deceleration in the solar wind.

Findings

The viscosity-based model matches observed CME deceleration.

The model predicts CME velocity profiles consistent with observations.

It offers a physical basis for CME drag, replacing empirical coefficients.

Abstract

The forces acting on solar Coronal Mass Ejections (CMEs) in the interplanetary medium have been evaluated so far in terms of an empirical drag coefficient $C_{\rm D} \sim 1$ that quantifies the role of the aerodynamic drag experienced by a typical CME due to its interaction with the ambient solar wind. We use a microphysical prescription for viscosity in the turbulent solar wind to obtain an analytical model for the drag coefficient $C_{\rm D}$. This is the first physical characterization of the aerodynamic drag experienced by CMEs. We use this physically motivated prescription for $C_{\rm D}$ in a simple, 1D model for CME propagation to obtain velocity profiles and travel times that agree well with observations of deceleration experienced by fast CMEs.