tokens: 3 (c)) accompanied by large fluctuations in the proton density and temperature (Figures 1 (d)–(e)). The coexistence of kinetic Alfvén waves and Alfvén ion cyclotron waves was demonstrated in this slow solar wind during 2018 November 6 (Huang et al. 2020a ), similarly to the observations in the fast solar wind at 1 au (e.g., He et al. 2011 , 2012 , 2015 : Podesta 2013 ; Bruno Telloni 2015 ). The plasma β varies from 0.1 to ∼10, but mostly less than 1 (Figure 1 (f)). Figure 1. Overview observations from 2018 November 4 to 6. (a) The magnitude of magnetic field, (b) the three components of magnetic field (c) the three components of the proton velocity in RTN coordinates, (d) the proton number density, (e) the proton temperature, (f) the proton β , and (g) the distance away from the Sun. To be able to study the magnetic energy spectra at the sub-ion scales for 15 minute windows, the Fourier transform was performed for the merged FGM and SCM measurements (Bowen et al. 2020a ) to obtain the magnetic energy spectra for each 15 minutes. The 15 minute duration ensures having at least one correlation time of the turbulent fluctuations (Parashar et al. 2020 ). Furthermore, to avoid possible “contamination” of the background turbulent spectra from intermittent but intense waves (e.g., ion cyclotron waves, whistlers), we excluded the magnetic spectra that showed clear spectral peaks from MHD to electron scales. One should point out that the electron measurements are not available during this time interval. But we can estimate the Doppler-shifted frequency of the electron inertial length f de ∼ 180 Hz and the Doppler-shifted frequency of the electron gyroradius f ρe ∼ 320 Hz based on the assumptions of N e = N i and T i / T e = 5. This indicates that the electron characteristic frequencies are larger than the Nyquist frequency of the magnetic field data provided by PSP, thus preventing us from investigating electron-scale turbulence. Figure 2 (a) presents an example of the resulting magnetic spectra. Three distinct frequency bands can be clearly evidenced: (i) the first one is an inertial range with the slope of −1.71 below 1 Hz, (ii) the second one is a steep ion transition range ( f −3.63 ) at the scales between the proton cyclotron frequency and the Doppler-shifted frequencies of the proton inertial length d i and gyroradius ρ i (i.e., f ∼[2, 9] Hz), (iii) the third one has a scaling f −2.68 between the ion and electron scales (∼[10, 60] Hz). These three distinct spectral features are also confirmed by all 219 selected spectra shown in Figure 2 (b). However, the spectral indices have large variations in the ion transition range. Figure 2. Power spectral densities of the magnetic field. (a) One example of magnetic spectrum during the time interval from 11:13:11 UT to 11:28:11 UT on 2018 November 6; (b) all selected spectra. The three vertical arrows from left to right correspond to the proton cyclotron frequency f ci , the Doppler-shifted frequency of the
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