Panel a: PSP measured radial magnetic field BR over the first PSP encounter. The magnitude scales approximately as 1/r2 (red dotted lines; also in panel b. We highlight the rapid large-amplitude polarity reversals (δBR/|B| of the order of 1). Panel b: one-hour statistical modes of BR (bisymmetric logarithmic plot) show the large-scale radial field colored for polarity (red, outward; blue, inward). Predicted radial-field profiles from a PFSS model are shown in green and black (SS at 2.0 and 1.2 RS respectively). Adapted from Bale et al. (2019).