Fluctuation Amplitudes of Magnetic-field Directional Turnings and Magnetic-velocity Alignment Structures in the Solar Wind

Abstract

Magnetic-field directional turning (MFDT) and magnetic-velocity alignment structure (MVAS) are two typical types of structures in the solar wind. However, their fluctuation amplitudes in different turbulence states have not been studied before. Here, we present the amplitude distributions of MFDTs and MVASs in the plane, where is the correlation coefficient between magnetic-field and velocity fluctuations multiplied by the sign of the x component of the mean field in geocentric solar ecliptic coordinates, and σ r is normalized residual energy. Measurements from the WIND spacecraft in the slow solar wind during 2005–2009 are used for the analysis. The data are cut into intervals with duration of 6 minutes, and the intervals that are nearly incompressible are selected for analysis. We find that for the fluctuations with and −1 < σ r < −0.6, which are considered to be associated with MFDTs, the level contours of the pixel average amplitude of magnetic-field fluctuations in the plane show a horizontal-stripe feature with approximately km s−1 in Alfvén units. For the fluctuations with and −0.9 < σ r < −0.2, which are considered to be associated with MVASs, the level contours of the pixel average amplitude of velocity fluctuations show a vertical stripe feature with approximately km s−1. Consequently, the level contours of the pixel average amplitudes of Elsässer variables show “U” and “W” shapes, respectively. These results will help us to understand the nature of the fluctuations in the solar wind.

Turbulence and Waves in the Sub-Alfvénic Solar Wind Observed by the Parker Solar Probe during Encounter 10

“…In the region between the two sub-Alfvénic flows, PSP observed possible partial HCS crossings, where the magnetic field magnitude |B| decreases to near zero but without direction changes in the radial magnetic field B R . Low values of the normalized cross-helicity σ c and highly negative normalized residual energy σ r are observed near the partial HCS crossings, which are consistent with previous observations (Zhao et al 2021c) and suggest the presence of convected solar wind structures with near-zero velocity fluctuations (e.g., Tu & Marsch 1991;Wang et al 2020;Zhao et al 2020). 2.…”

Effect of Intermittent Structures on the Spectral Index of Magnetic field in the Slow Solar Wind

“…We also notice that in this case the fluctuation amplitude of the proton velocity is much smaller than the magnetic field (normalized residual energy σ r = −0.91), and the fluctuations between the velocity and the magnetic field are not well correlated (correlation coefficient cc = −0.11). These characteristics indicate that this case may be associated with magneticfield directional turning (Tu and Marsch, 1991;Wang et al, 2020). It is convected by the solar wind, and nearly has no velocity fluctuations.…”

Large Amplitude Switchback Turbulence: Possible Magnetic Velocity Alignment Structures

“…The nature of these fluctuations needs further study. A candidate may be the magnetic structures, reported by Wang et al (2020). The magnetic-velocity alignment structures may have a flux-tube texture (Borovsky 2020), which are possible remnants of coronal jets (Sterling & Moore 2020).…”

“…Tu et al (2016) presented the first two time series with high C vb values and low r A values, and suggested that these time series may represent convecting magnetic field structures in the solar wind. Wang et al (2020) first suggested the concept of magnetic-velocity alignment structures. They are magnetically dominated structures with high correlation between magnetic field fluctuations and velocity fluctuations-MVAS, of which C 0.8 0.9 vb -and 0.9 0.2 r ( ) ( ) s~---.…”

“…The normalized cross-helicity c s , normalized residual energy r s , correlation coefficient C vb between v A d and v d , and Alfvén ratio r A are all dimensionless parameters to describe the state of solar wind turbulence (Tu & Marsch 1995;Wang et al 2020). They are defined as…”