Movie_1.mp4: The development of the perturbation streamfunction $\psi$ for a prograde surface quasi-geostrophic modon moving along a slope of $\lambda = 0.8$. The modon moves to the left generating a Rossby wave wake. The equations are integrated in a frame moving to the left at constant speed unity and the modon is initialised using the steady solution for $(\lambda,U,a) = (0,-1,1)$. Around $t = 25$ the modon begins to breakdown into a pair of coupled monopolar vortices with unmatched vortex strengths and ceases to move in a straight line to the left.

Movie_2.mp4: The development of the perturbation streamfunction $\psi$ for a vortex moving along a coastal boundary on a bottom slope of $\lambda = 0.8$. The vortex is modelled as a prograde surface quasi-geostrophic modon on the domain $y < 0$. The vortex moves to the left generating a Rossby wave wake and does not breakdown over the timescale studied. The equations are integrated in a frame moving to the left at constant speed unity and the vortex is initialised using the steady modon solution for $(\lambda,U,a) = (0,-1,1)$.