Magnetic field fluctuations during the sheath on March 15, 2019. From top to bottom: (a) the magnetic field magnitude (black) and three magnetic field components in RTN (blue: B_R, green: B_T, pink: B_N), (b) the ion cyclotron timescale (t_ci) and the ratio of the Alfvén speed to solar wind speed (v_A/v), (c) the wavelet PSD of magnetic field fluctuations in the periods of 1 s to 2 h (∼0.1 mHz–1 Hz frequency range), (d) the normalised magnetic field fluctuations (δB/B), (e) the fluctuation compressibility (δ|B|/δB), and (f) the PVI. The properties at three different MHD timescales (14 s, 56 s, and 223 s) are shown in panels d–f. Panels b, d, and e: values are calculated with a 20-min window sliding in 5-min steps through the investigated interval. The horizontal line in panel f marks the value PVI = 3. The vertical dashed line marks the shock, and the solid line shows the ICME leading edge, similar to Fig. 1.