Panels a and b: angular position and radial velocity of the ejecta leading edge derived from the 3D pp map and the radial velocity map, respectively, from 15:29 UT to 22:49 UT on 3 April 2010. Different colors represent different times. The thick black curve in panel a is the temporally averaged HEE longitude (ϕ) vs. HEE latitude (λ) of the CME front at this period of time. Panel c: angular distribution of the radial velocity of the simulated background solar wind in HEE coordinates with the ENLIL code at 9:56 UT on 3 April 2010 at a heliocentric distance of 30 R_⊙. The dotted white box highlights the fast-to-slow streaming interaction region. The thick white curve corresponds to the thick black curve in panel a. The radial velocity of the background solar wind along the thick white line in panel c is plotted in panel b as the thick black curve.