Fourier amplitude map F₂(R, t) within 8 kpc, computed from the time evolution of the radial Fourier profiles of the m = 2 mode. Snapshots were taken every 0.01 Gyr over a total of 4 Gyr (400 snapshots). To enable direct comparison across models, the color scale inside the color bar is fixed across all panels, such that the same color corresponds to the same amplitude value between 0 and 0.4. All values above 0.4 are shown in the same saturated red.