Back mapping polarity measure for streamer belt and sector reversal wind. Ballistic back mapping was performed from ACE to the source surface during period 1 (CR2041−CR2055, 2006, declining solar activity). The colored pixels give the value at their center positions (black dots) in 2% increments. A contour plot bi-linearly interpolating between these values has been drawn on top. Lines marking model parameters of constant equatorial source surface height have been inserted for r_ss, equ = 2.5 R_⊙ (solid gray line), for r_ss, equ = 2.0 R_⊙ (dotted gray line), and for r_ss, equ = 3.0 R_⊙ (dashed gray line). The black symbols mark the parameters for the example source surfaces from Fig. 1.