3D Feature of Self-correlation Level Contours at 10¹⁰ cm Scale in Solar Wind Turbulence

Abstract

The self-correlation level contours at 10 10 cm scale reveal a 2-D isotropic feature in both the slow solar wind fluctuations and the fast solar wind fluctuations. However, this 2-D isotropic feature is obtained based on the assumption of axisymmetry with respect to the mean magnetic field. Whether the selfcorrelation level contours are still 3-D isotropic remains unknown. Here we perform for the first time a 3-D self-correlation level contours analysis on the solar wind turbulence. We construct a 3-D coordinate system based on the mean magnetic field direction and the maximum fluctuation direction identified by the minimum-variance analysis (MVA) method. We use data with 1-hour intervals observed by WIND spacecraft from 2005 to 2018. We find, on one hand, in the slow solar wind, the self-correlation level contour surfaces for both the magnetic field and the velocity field are almost spherical, which indicates a 3-D isotropic feature. On the other hand, there is a weak elongation in one of the perpendicular direction in the fast solar wind fluctuations. The 3-D feature of the self-correlation level contours surfaces cannot be explained by the existed theory.

Dependence of 3D Self-correlation Level Contours on the Scales in the Inertial Range of Solar Wind Turbulence

“…For both the magnetic field and the velocity, the correlation functions of the slow wind decrease more rapidly than that of the fast wind for both 30 minutes and 10 minutes 0.00 0.25 0.50 0.75 1.00 intervals. This difference between the slow and fast wind has already been shown for 1 hour intervals in Wu et al (2019), where 23083 intervals in the slow wind and 3347 intervals in the fast wind are investigated.…”

“…In Figure 2(d), the fast wind velocity field self-correlation level contour surface has a similar shape with that of magnetic field. The size difference of the surface remains for 30 minutes intervals as for 1 hour intervals shown in Wu et al (2019): the r level is longer for the fast wind than for the slow wind and longer for the magnetic field than for the velocity. We also analyzed the 3-D self-correlation level contours in the In the left panel of Figure 4, we show r c /r c ⊥ with interval durations = 1 hour, 30 minutes and 10 minutes for the magnetic field (solid circles) and the velocity field (solid triangles) measured by Wind spacecraft for both the slow (red) and fast (black) winds.…”

“…Wang et al (2019) extended this study using the same data set and found that the anisotropy disappears and it becomes 2-D isotropic for both the slow wind and the fast wind with the intervals duration decreasing from 2 days, 1 day, 10 hours, 2 hours, 1 hour. Wu et al (2019) further extended the self-correlation function level contours analysis using 1-hour intervals observed by WIND spacecraft. They show a 3-D isotropic self-correlation function level contours in the slow wind and a 3-D quasi-isotropic self-correlation function level contours in the fast wind.…”

Isotropic Scaling Features Measured Locally in the Solar Wind Turbulence with Stationary Background Field

“…However, they did not investigate the scaling anisotropy. The scaling isotropy we found here is consistent with the isotropic 3D self-correlation level contours of the magnetic field and the velocity in the fast wind shown in Wu et al (2019aWu et al ( , 2019b. Wang et al (2015) selected the low-amplitude time series so that the time series are time stationary and investigated their scaling anisotropy.…”

Topology of Magnetic and Velocity Fields at Kinetic Scales in Incompressible Plasma Turbulence

“…In the framework of space plasmas, both the solar wind and the planetary magnetosheath plasmas provide natural laboratories for studying plasma turbulence. Based on in situ observations from various orbiting spacecraft, several aspects of plasma turbulence have been well investigated in the past decades such as the spectral features (e.g., Alexandrova et al., 2009, 2021; Andrés et al., 2020, 2021; Chen et al., 2020; Huang et al., 2014, 2017, 2021), intermittency (e.g., Andrés et al., 2022; Bruno, 2019; Greco et al., 2008, 2009; He et al., 2019; Huang, Zhang, et al., 2022; Osman et al., 2010, 2012), and anisotropy (e.g., Chen et al., 2012; Duan et al., 2021; Horbury et al., 2008; Huang, Xu, et al., 2022; Sahraoui et al., 2004, 2010; Verdini et al., 2018; Wang et al., 2015, 2019; Wicks et al., 2011; Wu et al., 2019; Zhang et al., 2022). Some of those studies required using the multi‐spacecraft missions Cluster and Magnetospheric MultiScale (MMS) to estimate three‐dimensional structures and spatial anisotropies of the magnetic and velocity fields.…”