effects of different deactivation of the force on the flow, see Figure \[fig:different\_deactivation\]. We compared a sharp deactivation and a gradual deactivation with the strength given by a tanh function, $0.5-0.5\text{tanh}((t-t_0)/25)$, where $t$ is time and $t_0$ is the nominal deactivation time instant, i.e. the instant when the strength halves. With this strength function, the force decreases smoothly to zero in approximately 100 time units. The sharp deactivation is at $t=400$ and the smooth one is at $t_0=450$ in panel (a). These two deactivation are applied to the simulation we have shown in Figure \[fig:KE\_no\_noise\] to show the effect on the base flow. Panel (b) shows the kinetic energy of the flow, which immediately decreases after the force is removed or reduced without any sign of turbulent fluctuations. Panel (c) shows the streamwise velocity at the center of the forcing area in the $x-z$ cut plane of $y=-0.5$. Similarly, there is no sign of turbulent fluctuations induced by the deactivation. Therefore, the results indicate that the deactivation, no matter being sharp or gradual, does not cause any instabilities or turbulent velocity fluctuations, and therefore does not contribute to the generation of bands. Besides, we also tested the two deactivation after 