Illustration for the method of backmapping. Left: View of the sun from the north (N). The longitude of the spacecraft (S) is marked by A. When the emitted solar wind is detected by the spacecraft, the sun has continued to rotate by the angle ΔΦ leading to the backmapped longitude marked by B. Then, r and r₀ are the heliocentric distance of the spacecraft and of the source surface at 2.5 solar radii, respectively. Right: GONG-map of carrington rotation 2184.0 (top; note: the map has been mirrored in order to have the time running from left to right). The in situ solar wind speed and magnetic polarity as measured at 1 AU and the backmapped data according to Eq. (1) (bottom). It is evident that the high speed streams of the backmapped data can be associated more accurately with the respective CH.