Fluctuation Amplitudes and Spectral Indices of Magnetic Field Directional Turnings and Magnetic-Velocity Alignment Structures in the Slow Solar Wind Turbulence

Magnetic field directional turning (MFDT) and magnetic-velocity alignment structure (MVAS) are two typical types of structures in the solar wind. However, the fluctuation amplitudes and spectral indices of them in different turbulence states have not been studied before. Here, we first present the amplitude and spectral-indices distributions of MFDTs and MVASs in C_vb - σ_r plane, where C_vb is correlation coefficient between magnetic field and velocity fluctuations multiplied by the sign of x component of mean field in geocentric solar ecliptic coordinates, and σ_r is normalized residual energy. Measurements from the WIND spacecraft at 1 AU in the slow solar wind during 2005-2009 are used for analysis. The data are cut into intervals with duration of 6 minutes for the amplitude analysis. We find that for the fluctuations with |C_vb| < 0.55 and -0.9 < σ_r < 0, which are considered as being 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 10|σ_r| km s^-1 in Alfvén unit. For the fluctuations with |C_vb| > 0.85 and -0.9 < σ_r < -0.2, which are considered as being associated with MVASs, the level contours of the pixel average amplitude of velocity fluctuations show a vertical-stripe feature with approximately 58.6|C_vb|-47.5 km s^-1. Consequently, the level contours of the pixel average amplitudes of Elsässer variables z^± show "U" and "W" shapes, respectively. For the spectral analysis, we cut the data into intervals with duration of 1 hour. We find that in the inertial range between 10^-3 Hz and 0.05 Hz, the spectral indices of typical MFDTs (|C_vb| < 0.5 and -1 < σ_r < -0.85) are significantly different from those of typical MVASs (|C_vb| > 0.9 and -0.7 < σ_r < -0.2). The indices of magnetic spectra for them are -1.83±0.12 and -1.67±0.14, respectively. The indices of velocity spectra for them are -1.23±0.20 and -1.50±0.13, respectively. Using the data measured by Parker Solar Probe at the perihelion in the slow solar wind, we also do the same analyses. These results will help us to understand about the nature of the fluctuations in the solar wind.