Evolution of Alfvénic Fluctuations inside an Interplanetary Coronal Mass Ejection and Their Contribution
to Local Plasma Heating:Joint Observations from 1.0 to 5.4 au
Hui Li;Chi Wang;John D. Richardson and Cui Tu
Published 2017 December
The Astrophysical Journal Letters, Volume 851, Number 1
Abstract
Tracking an interplanetary coronal mass ejection (ICME) by widely separated spacecraft could provide us with a good opportunity to study the evolution of embedded Alfvénic fluctuations (AFs) and their possible contribution to local plasma heating directly. In this study, an ICME observed by Wind at 1.0 au on 1998 March 4–6 is tracked to the location of Ulysses 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 × 10−4 to 5 × 10−2 Hz. When the ICME propagates to 5.4 au, the Aflvénicity decreases significantly, and AFs are rare and only found at a few localized frequencies with the occurrence rate decreasing to 3.0%. At the same time, the magnetic strength at the AF-rich region has an extra decrease in addition to the ICME expansion effect. The energetics of the ICME are also investigated here. Under similar magnetic strength situations at 1.0 au, the turbulence cascade rate at the AF-rich region is much larger than the one at the AF-lack region. Moreover, it can be maintained during the decrease of magnetic strength if there is a lack of AFs. However, when many AFs exist, it reduces significantly as the AFs disappear. The turbulence cascade dissipation rate within the ICME is inferred to be 2688.6 J kg−1 s−1, which satisfies the requirement of local ICME plasma heating rate, 1653.2 J kg−1 s−1. It is therefore concluded that AF dissipation is responsible for extra magnetic dissipation and local plasma heating inside the ICME.
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