Top panel: computed maximum inclination of the heliospheric current sheet illustrating the flip of the global magnetic field for 1976–2012 (Carrington rotations 1642–2132). The solid line is the simulation with the classic PFSS model using the line-of-sight boundary condition in the photosphere including significant polar field correction; the dashed line is the model with higher source surface radius R _S = 3.25, it uses a radial boundary condition at the photosphere without polar field correction. Bottom panel: the total strength of the first three multipole components (dipole, quadrupole, and octupole, from top to bottom respectively) of the solar magnetic field during Carrington rotations 1642–2132. The data was provided by the Wilcox Solar Observatory (http://wso.stanford.edu).