Amplitude in across the annular region shown in Fig. 9, throughout the simulation time, represented as a boxplot (left). The whole time series is unraveled in the right panel. It is sampled every 2 orbital periods (the output rate of our simulations). Although the first run is remarkably constant, runs 3 to 5 exhibit significant dispersion within this metric, while the mean value (green crosses) itself is stabilized. The period of these oscillations corresponds to the life cycle of a secondary spiral arm, illustrated in Fig. 11.