Panel (a): 2D histogram of velocity gradients’ orientation and velocity’s convergence using A2 simulation at t_r ≃ 0.0 Myr. Here, p gives the volume fraction of each data point. Panel (b): 2D histogram of velocity gradients’ orientation and projected velocity’s convergence using simulation A2 at t_r ≃ 3.4 Myr. Here, p gives the volume fraction of each data point and bin size is 200 for the 2D histograms. Note that the orientation is measured in typical Cartesian coordinate, i.e., with respect to the right horizontal direction.