ICME event observed by ACE from December 16 to December 17, 2006. Upper panel, from top to bottom: Temporal variation in the total IMF (the interplanetary magnetic field) B_T, IMF vector B_vec = (B_x, B_y, B_z), azimuthal (ϕ = tan⁻¹(B_y/B_x)) and elevation ($\theta ={tan}^{-1}(Bz./\sqrt{Bx{.}^2+By{.}^2}$) angles of the IMF in the Geocentric Solar Ecliptic coordinate system, solar wind speed (V_p), proton number density (N_p), magnetic fluctuation (δB(t) = |B(t + Δt)−B(t − Δt)|/2), plasma temperature (T_p), and proton beta (β_p). The first vertical black line marks the ICME shock onset. The yellow-shaded region highlights the ICME sheath, while the blue-shaded region indicates the MO. Lower panel: log P_th versus log N_p for plasma protons within the MO region. The coloured circles represent data points (colour-coded according to their observation time), and the dashed black line gives a linear fitting value.