Multi-spacecraft comparison at 1 au. Panel (a): Temporal variations of O_R (using the same 27-day sliding window in Fig. 1) observed by ACE (blue), Wind (red), STEREO-A (orange), and STEREO-B (green). Panels (b)-(c): V_SW and O_R (using the same 2-day sliding window in Fig. 2) for the time intervals corresponding to the shaded regions in panel (a). The dashed black lines mark the onset times of the HSS observed by ACE, defined as the moments when V_SW exceeds 500 km/s (accurate to the hour). Panels (d)-(g): Time-series superposition of the two sets of distinct 27-day repeating HSS intervals from (b)-(c), aligned at their respective onset times (t = 0).