Global configuration of the IP shock in the equatorial plane estimated from in situ observations. The approximate shape of the IP shock is indicated with the black bold straight and dashed lines (details given in the main text). The arrows represent the shock normals, and the configuration of the shock is indicated as oblique or quasi-perpendicular. The Parker spirals connecting each spacecraft are calculated using the in situ solar wind speed observed at the locations of STEREO-A (also used for MESSENGER) and STEREO-B at the time given in the plot legend. The Earth (not to scale) is given for reference, and the Sun at the centre is indicated with the yellow circle (not to scale).