Time series of Encounter 4 turbulence properties: rms magnetic fluctuation δB_rms, normalised rms fluctuation δB∕B₀, magnetic compressibility C_B, magnetic spectral index α_B, cross helicityσ_c, residual energy σ_r, magnetic field angle to the radial θ_BR, Taylor hypothesis parameter ϵ, and predicted angular distance to the heliospheric current sheet ϕ_HCS. The red line is a ten-point running mean of α_B. Values of ϵ for which the Bourouaine & Perez (2019) model is valid are marked with blue dots and points for which it is not valid are marked as red crosses. The vertical dashed lines indicate the intervals used to calculate the spectra in Fig. 6.