Mini-Beast: Blizzard at Carlisle Bus Station

We're in the grip of another cold snap. I found a wonderful 1 minute film that explains what has happened to the polar vortex http://www.bbc.co.uk/news/av/science-environment-43172539/why-the-uk-is-so-cold I was interested in the idea that as the winds move more slowly the radius of the circulation decreases. This is the opposite of a spinning ice skater, where pulling her arms in makes her spin faster. In her case, angular momentum is conserved. i'm guessing that angular momentum is not conserved in the polar vortex so dissipative forces must be acting. As the air slows down it will become more dense as particles come together. This is part of the explanation of the aerofoil shape and lift on a plane wing. Here the increased density would explain why the block of air sinks.