Radial velocity contour plots from the ENLIL simulation in the ecliptic plane. The black and white dashed lines represent the IMF lines and the black contours track the ICMEs. The white lines correspond to the HCS, which separates the regions with opposite magnetic polarity, shown in blue (negative) or red (positive) on the outer edge of the simulation region. Left panel (a): magnetic connectivity of the different spacecraft around the particle solar release time. Right panel (b): magnetic field line connecting STEREO-B intersects for the first time the IP shock driven by the ICME. Credit: CCMC.