Don't think of it as an air ring. Think of it as a water ring with air trapped in it. The volume of water making up the vortex is much larger than the air volume.
(The dynamics are the same as a smoke ring. I was once watching fireworks on a roof and an eight-foot smoke ring drifted down from the range, ring over our heads.)
In principle I see how it works--thinking about an individual air bubble being dragged around by the water vortex ring makes that clear--it just amazes me that the actual ratio of forces involved is such that these rings can be so large and stable for such long times. I wouldn't have thought the viscous boundary layer at the air-water interface was up to the job, although it obviously doesn't much care what I think!
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(The dynamics are the same as a smoke ring. I was once watching fireworks on a roof and an eight-foot smoke ring drifted down from the range, ring over our heads.)
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