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

Abstract

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.