Velocities in the latitudinal centers of HSSs, belonging to coronal holes with areas of 1 (blue), 2 (red), 4 (green), and ﹩8\times {10}^{10}\,{\mathrm{km}}^{2}﹩ (yellow). (a) Snapshots of the radial velocity profile, taken at 1 day (dotted), 2.25 days (dashed), and 3.5 days (solid lines) after the center of the coronal hole has crossed the central meridian. (b) Velocity of the stream interface ﹩{v}_{\mathrm{SI}}﹩ derived by its radial displacement with time vs. the distance of the stream interface to the Sun. (c) Peak velocity v_p of the HSS vs. the radial distance of the location of the peak velocity to the Sun.