Cross Helicity of the November 2018 Magnetic Cloud Observed by the Parker Solar Probe

Magnetic clouds are large-scale transient structures in the solar wind with low plasma \(\beta\), low-amplitude magnetic field fluctuations, and twisted field lines with both ends often connected to the Sun. Their inertial-range turbulent properties have not been examined in detail. In this Letter,...

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Bibliographic Details
Published in:arXiv.org 2020-08
Main Authors: Good, S W, Kilpua, E K J, Ala-Lahti, M, Osmane, A, Bale, S D, L -L Zhao
Format: Article
Language:English
Subjects:
Amplitudes
Helicity
Magnetic clouds
Residual energy
Solar probes
Solar wind
Wave power
Online Access:Get full text
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Summary:Magnetic clouds are large-scale transient structures in the solar wind with low plasma \(\beta\), low-amplitude magnetic field fluctuations, and twisted field lines with both ends often connected to the Sun. Their inertial-range turbulent properties have not been examined in detail. In this Letter, we analyze the normalized cross helicity, \(\sigma_c\), and residual energy, \(\sigma_r\), of plasma fluctuations in the November 2018 magnetic cloud observed at 0.25 au by the Parker Solar Probe. A low value of \(|\sigma_c|\) was present in the cloud core, indicating that wave power parallel and anti-parallel to the mean field was approximately balanced, while the cloud's outer layers displayed larger amplitude Alfvénic fluctuations with high \(|\sigma_c|\) values and \(\sigma_r\sim0\). These properties are discussed in terms of the cloud's solar connectivity and local interaction with the solar wind. We suggest that low \(|\sigma_c|\) is likely a common feature of magnetic clouds given their typically closed field structure. Anti-sunward fluctuations propagating immediately upstream of the cloud had strongly negative \(\sigma_r\) values.
ISSN:2331-8422
DOI:10.48550/arxiv.2008.07868