Modal plots for moment-1 maps constructed from beam-convolved datacubes. From left to right, we show modal plots associated with the J = 2 − 1 transitions of ¹²CO, ¹³CO, and C¹⁸O, respectively, fixing the inclination to 0^◦. We indicate the planet’s radial location in each case with a dotted line. As in Fig. 7, the shadow-driven case is above, while the planet-driven case is below. Shadow-driven spirals show an m = 2 mode steadily decreasing in strength with deeper and deeper isotopologues.