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Magnetic and Velocity Fluctuations in the Near-Sun Region from 0.1-0.3 au Observed by Parker Solar Probe

AuthorWu, Honghong; Tu, Chuanyi; Wang, Xin; Yang, Liping;
KeywordsParker Data Used; 1873; 830
AbstractThe fluctuations observed in the slow solar wind at 1 au by the WIND spacecraft are shown by recent studies to consist of mainly magnetic-field directional turning and magnetic-velocity alignment structure (MVAS). How these structures are created has been a question because the nature of the fluctuations in the near-Sun region remains unknown. Here, we present an analysis of the measurements in the slow solar wind from 0.1-0.3 au by Parker Solar Probe during its first six orbits. We present the distributions in the $C_\mathrmvb^\prime \mbox—\sigma _r$ plane of both the occurrence and average amplitudes of the fluctuations, including the magnetic field, the velocity, and the Elsässer variables, where $C_\mathrmvb^\prime $ is the correlation coefficient between the magnetic and velocity fluctuations multiplied by the opposite sign of the radial component of the mean magnetic field and \ensuremath\sigma $_ r $ is the normalized residual energy. We find that the dominant composition is the outward- propagating Alfv\ enic fluctuations. We find Alfv\ enic fluctuations with $C_\mathrmvb^\prime 0.95$ , in which the amplitudes of z $^+$ reach 60 km s$^-1$ and those of z $^-$ are close to the observational uncertainty. We also find a region with high $C_\mathrmvb^\prime $ and moderate minus \ensuremath\sigma $_ r $ in which the fluctuations are considered MVAS being magnetic dominated with the amplitude of magnetic fluctuations reaching 60 km s$^-1$. We provide empirical relations between the velocity fluctuation amplitude and $C_\mathrmvb^\prime $ . The comparison between these results and those observed at 1 au may provide some clues as to the nature and evolution of the fluctuations.
Year of Publication2021
Number of Pages92
Date Publisheddec