Figure 8.

Contour plot of the instantaneous vorticity field for case $h_0=c,{\theta }_0={15}^{\circ }$ and $St=0.1935$. (a) $\psi ={45}^{\circ }$; (b) $\psi ={60}^{\circ }$; (c) $\psi ={75}^{\circ }$; (d) $\psi ={90}^{\circ }$; (e) $\psi ={105}^{\circ }$; (f) $\psi ={120}^{\circ }$; (g) $\psi ={150}^{\circ }$; (h) $\psi ={170}^{\circ }$.