Time evolution of turbulent fraction Ft(t) and of fluctuating velocity fields visualized at mid-gap, for h = 0.1 with an artificially extended azimuthal domain size of \(L_\theta = 128 \pi\). On the right column, contours show x-\(\theta\) distributions of the radial velocity fluctuation \(u_r'\) normalized by the inner-cylinder velocity Uw. Top (orange box and curve in the graph) : above the global critical Reynolds number Reg. Middle (red) : near Reg. Bottom (black) : below Reg.