Turbulent Modes in Slow, Alfvénic Slow, and Fast Solar Wind at 1 au

Abstract The characterization of solar wind fluctuations provides insight into magnetofluid turbulence. The slow solar wind with high Alfvénicity, the Alfvénic slow solar wind (ASSW), possesses a similar bulk speed as the slow wind, but with fluctuations largely similar to those found in the fast wind. ASSWs have attracted less attention from the turbulence community compared to fast wind flows. G. P. Zank et al. developed a linear mode decomposition (LMD) technique that identifies eight modes in the magnetized solar wind plasma, namely entropy, fast and slow (+/−) magnetosonic (MS), Alfvén (+/−), and magnetic island modes. Using the LMD technique, we present a comparative study of the characteristic modes found in the ASSW, classical slow solar wind (CSSW), and fast solar wind (FSW) events identified by the WIND spacecraft. We investigate the properties of the eight magnetohydrodynamic modes and their spectral characteristic differences in the three solar wind plasma environments at 1 au. We show that in the CSSW, ASSW, and FSW intervals (i) fast MS mode density fluctuations are dominant compared to entropy and slow MS modes, (ii) magnetic island modes clearly dominate Alfvén modes for the transverse fluctuating magnetic field, and (iii) slow MS modes show no significant power spectral density contribution compared to the Alfvén and fast modes in the frequency spectra for velocity fluctuations. The ASSW exhibits characteristics intermediate to the CSSW and FSW in entropy modes, compressibility, the magnetic island-to-Alfvén mode magnetic energy ratio, and kinetic variance anisotropy and magnetic energy variance anisotropy corresponding to Alfvén modes.