Synoptic maps of the radial magnetic field B_r (nT) at the inner radial boundary (∼0.14 AU) for CR2190 (top-left), CR2202 (top-right), CR2210 (bottom-left), and CR2221 (bottom-right). For each panel, the horizontal axis is the longitude, and the vertical axis is the latitude in the Carrington coordinate system. The black line in each panel is the contour of the radial magnetic field drawn at B_r = 0, which marks the location of the heliospheric current sheet.