Ratio of ﹩{v}_{{\rm{z}}}﹩ to the Kelperian velocity at the footprint of the flow, plotted against χ, for launch angles ﹩{\theta }_{{\rm{o}}}=20^\circ ﹩ (solid), ﹩30^\circ ﹩ (dotted), and ﹩40^\circ ﹩ (dashed). The Alfvén critical points (X) and position of the UFO (U) are indicated for all three. Note that for ﹩{\theta }_{{\rm{o}}}=40^\circ ﹩, the UFO is at a sub-Alfvénic point.