Fourier transforms of moment-1 maps constructed from beam-convolved ¹²CO J = 2 − 1 datacubes. As in Fig. 2, we plot the shadow-driven case in the upper row, and the more standard planet-driven case in the lower, with inclinations of 0^◦, 30^◦, and 60^◦ (from left to right). We indicate the planet’s radial location in each case with a dotted line. For the shadow-driven spiral, the power is most concentrated in even-numbered modes, a feature absent from the classical case; however, this distinction becomes less apparent in the inclined cases. To avoid contamination of the mode structure due to emission from the (unphysically situated) outer radial boundary of the simulation, we clip large radii from our plot for the i_d = 30^◦ and 60^◦ cases.