Evolution of Alfv\'enic fluctuations inside an interplanetary coronal mass ejection and their contributions to local plasma heating: Joint observations from 1.0 AU to 5.4 AU

TL;DR

This study tracks the evolution of Alfvénic fluctuations inside an interplanetary coronal mass ejection from 1.0 to 5.4 AU, showing their significant role in magnetic dissipation and local plasma heating.

Contribution

It provides the first direct observational evidence of how Alfvénic fluctuations diminish with distance inside an ICME and their contribution to plasma heating.

Findings

AF occurrence rate decreases from 21.7% to 3.0% with distance.

Turbulence cascade rate is higher in AF-rich regions.

AF dissipation accounts for the local plasma heating requirement.

Abstract

Directly tracking an interplanetary coronal mass ejection (ICME) by widely separated spacecrafts is a great challenge. However, such an event could provide us a good opportunity to study the evolution of embedded Alfv\'enic fluctuations (AFs) inside ICME and their contributions to local plasma heating directly. In this study, an ICME observed by Wind at 1.0 au on March 4-6 1998 is tracked to the location of Ulysess at 5.4 au. AFs are commonly found inside the ICME at 1.0 au, with an occurrence rate of 21.7% and at broadband frequencies from 4$\times 10^{-4}$ to 5$\times 10^{-2}$ Hz. When the ICME propagates to 5.4 au, the Aflv\'enicity decreases significantly, and AFs are rare and only found at few localized frequencies with the occurrence rate decreasing to 3.0%. At the same time, the magnetic field intensity at the AF-rich region has an extra magnetic dissipation except ICME expansion effect. The energetics of the ICME at different radial distance is also investigated here. Under similar magnetic field intensity situations at 1.0 au, the turbulence cascade rate at the AF-rich region is much larger than the value at the AF-lack region. Moreover, it can maintain as the decrease of magnetic field intensity if there is lack of AFs. However, when there exists many AFs, it reduces significantly as the AFs disappear. The turbulence cascade dissipation rate within the ICME is inferred to be 1622.3 $J\cdot kg^{-1}\cdot s^{-1}$, which satisfies the requirement of local ICME plasma heating rate, 1653.2 $J\cdot kg^{-1}\cdot s^{-1}$. We suggest that AF dissipation is responsible for extra magnetic dissipation and local plasma heating inside ICME.