Comparison of the model rolling predictions (top row of each panel) of the radial velocity v_r on the solar equatorial plane with the corresponding MHD test-set true values (bottom row) in three representative test windows (a)–(c). The three windows are taken from different periods of the test set. The polar coordinate grid covers the heliocentric distance range of 25R_s–225R_s, with radial ticks in units of R_s and angular ticks indicating the heliographic Carrington longitude of each angular bin. The columns from left to right correspond to the consecutive rolling steps 1–5, each with Δt = 24 hr. The color scale indicates the magnitude of v_r; each panel uses a color-scale range determined by the 2nd–98th percentiles of its own data.