Evolution of HSS properties with distance from the Sun. Top left: schematic cross section of an HSS at 0.1 AU with a longitudinal width of 22°. Top right: peak velocity of the HSS versus its distance from the Sun. Bottom: temperature (left) and density (right) of the associated HSS plasma parcels versus the distance from the Sun. The HSS properties have been derived at latitudinal displacements of 0° (blue), 4° (orange), 6° (green), 8° (red), and 10° (purple) to the center of the HSS. The dashed vertical lines mark the distance at which the plasma parcels start to originate from the trailing boundary region.