Solar cycle evolution of the solar wind footpoints. The top two panels show the fraction of open field lines, in each Carrington rotation, that trace down through the PFSS from a uniform distribution in latitude–longitude at the source surface to a given latitude bin at the surface (width ∼2°) using WSO magnetograms (1976–2022) and SOHO/MDI & SDO/HMI magnetograms (1996–present), respectively (the longitudinal information is ignored, and the connectivity sums to 100% for each Carrington rotation). The third panel displays a combined radial magnetic field butterfly diagram, in which the pole-ward surges of magnetic flux are easily distinguished. The bottom row displays the monthly sunspot number during this time, taken from WDC-SILSO, along with the contributions from the northern and southern hemispheres individually.