Plasma heating inside ICMEs by Alfvenic fluctuations dissipation

TL;DR

This study investigates the presence and role of Alfvenic fluctuations inside interplanetary coronal mass ejections (ICMEs) using Voyager 2 data, revealing their frequent occurrence and potential contribution to plasma heating.

Contribution

It provides the first comprehensive report on Alfvenic fluctuations inside ICMEs and analyzes their spatial distribution and evolution with distance from the Sun.

Findings

AFs frequently occur inside ICMEs, especially near centers and boundaries.

The duration of AFs decreases linearly as ICMEs expand outward.

AF occurrence rate inside ICMEs is lower than in ambient solar wind.

Abstract

Nonlinear cascade of low-frequency Alfvenic fluctuations (AFs) is regarded as one candidate of the energy sources to heat plasma during the non-adiabatic expansion of interplanetary coronal mass ejections (ICMEs). However, AFs inside ICMEs were seldom reported in the literature. In this study, we investigate AFs inside ICMEs using observations from Voyager 2 between 1 and 6 au. It is found that AFs with high degree of Alfvenicity frequently occurred inside ICMEs, for almost all the identified ICMEs (30 out of 33 ICMEs), and 12.6% of ICME time interval. As ICMEs expand and move outward, the percentage of AF duration decays linearly in general. The occurrence rate of AFs inside ICMEs is much less than that in ambient solar wind, especially within 4 au. AFs inside ICMEs are more frequently presented in the center and at the boundaries of ICMEs. In addition, the proton temperature inside ICME has a similar distribution. These findings suggest significant contribution of AFs on local plasma heating inside ICMEs.