Drift of grown dust toward the spiral arms. The first and second panels (from left to right) present the residual dust velocity field superimposed on the gas and grown dust surface densities, respectively (in log g cm⁻²). The third and fourth panels show the Stokes numbers and maximum size of dust grains (in log cm), respectively. The dotted circles indicate the position of corotation of the spiral pattern with the gas disk. The black contour lines outline the position of the spiral for convenience.