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

• Published in: Astrophysical journal. Letters Vol. 900; no. 2; p. L32
• Main Authors: Good, S. W., Kilpua, E. K. J., Ala-Lahti, M., Osmane, A., Bale, S. D., Zhao, L.-L.
• Format: Journal Article
• Language: English
• Published: Austin The American Astronomical Society 01.09.2020; IOP Publishing
• Subjects: Amplitudes; Clouds; Fluctuations; Helicity; Interplanetary magnetic fields; Interplanetary turbulence; Magnetic clouds; Magnetic fields; Residual energy; Solar coronal mass ejections; Solar magnetic field; Solar probes; Solar wind; Wave power
• ISSN: 2041-8205; 2041-8213
• DOI: 10.3847/2041-8213/abb021

Magnetic clouds are large-scale transient structures in the solar wind with low plasma-β, 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, c, and residual energy, r, of plasma fluctuations in the 2018 November magnetic cloud observed at 0.25 au by the Parker Solar Probe. A low value of was present in the cloud core, indicating that wave power parallel and antiparallel to the mean field was approximately balanced, while the cloud's outer layers displayed larger amplitude Alfvénic fluctuations with high values and r ∼ 0. These properties are discussed in terms of the cloud's solar connectivity and local interaction with the solar wind. We suggest that low is likely a common feature of magnetic clouds given their typically closed field structure. Antisunward fluctuations propagating immediately upstream of the cloud had strongly negative r values.