Evolution of the FR magnetic structure during its propagation. Panel a): 1D cuts of B_θ (in green) and B_φ (in red) at the nose of the thick1 (left) and thin3 (right) flux rope at 15, 30, 50, and 210 R_⊙ (from top to bottom). The black dashed line for each FR at 50 R_⊙ is a Gaussian fit of B_φ (see Sect. 4.1). The dots show the position of the seed streamline displayed in panel b) (of the corresponding color) projected on the B_φ profile. The x-axis decreases from left to right to facilitate comparison with Figs. 7 and 8. Panel b): Magnetic structure of the thick1 (left) and thin3 (right) cases. All streamlines originate from seeds that are on the () line. The radial position of each seed is shown in panel a). From purple to dark green, the streamlines start from the front of the flux rope and move to the back.