A smokestack at the origin continuously emits smoke that rises at constant speed $u$ relative to the surrounding air. The air is in steady state with a horizontal flow that depends only on height: still below $h_1$, blowing to the right at constant speed $v$ between $h_1$ and $h_2$, and still again above $h_2$. Smoke parcels move passively with the local air (rising at $u$ relative to it) and do not diffuse or mix. After the plume has reached its steady configuration, what is its shape?