¹²COJ = 2 − 1 lines, for the planet-driven spiral models (above) and the shadow-driven models (below), at a position R = 60 au and ϕ = 0 with respect to the x-axes of Fig. 4 (and, equivalently, of the qualitative maps in Fig. 6). In the initial condition, line broadening results exclusively from thermal motion, and is largely unaffected by beam convolution. In evolved disks, however, the line profile is shifted and broadened by vertical motions within spiral arms, with beam convolution over regions of differing velocity dampening the overall directional shift, while enhancing broadening.