An example number density structure. Top three panels: a 4 day overview of 10 min averaged radial proton bulk speed (v_r, top axis), radial magnetic field (B_r, middle axis), and proton number density (n_p, bottom axis). The HCS crossing is marked with a red dashed line between days 87 and 88. Bottom four panels: a shorter 1.5 h interval, with the structure present between the grey dashed lines. The top axis shows proton number density (n_p ), and the second axis proton plasma beta (β_p). The third axis shows proton parallel temperature (orange, T_p∥) and proton perpendicular temperature (blue, T_p⊥). The fourth axis shows the proton thermal pressure (red, p_p), magnetic pressure (blue, p_mag), and total pressure (grey, p_tot). The range of values in the total pressure is due to uncertainty in the number density and temperature of electrons and alpha particles.