= Solution
{c}
The <streamlines> are contours of $\psi$. Since $A<0$, the exact <streamfunction> is negative inside the rectangle and zero on its perimeter. It has one interior minimum, with closed anticlockwise <streamlines>: a broad northward interior flow returns southward along the west wall; flow is westward near the north edge and eastward near the south edge. The western parts of the <streamlines> are closely packed because the <western boundary current> is much faster.
\Image[/past-exam-of-the-physics-of-atmospheres-and-oceans-course-of-the-university-of-oxford/2021-pluto-streamlines.png]
{title=Exact linear-drag basin <streamlines> and flow direction for the specified <Pluto> parameters}
The figure uses the exact <ordinary differential equation> solution, so it also remains consistent with both wall conditions when the asymptotic scale separation is only moderate. It depicts the stipulated dynamical model, not observed winds or a reconstruction of the source illustration.
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