Chilly winds:
A few days ago we had a cold snap.  It had been predicted days in advance and was apparently of an unusual nature.  (Melting ice spurs wild weather NATURE vol. 504 no. 7479 December 12, 2013 page 190 citing Nature Clim. Change (2013)) It got as cold in Michigan as it is on Mars or at the south pole.  Some wrote in harrowing tones that it was as cold in some places as it had been in forty years.  That’s not so far off in time from when I was up north myself, so maybe I am under reacting.  Certainly we had no frost here in Florida, and frost has happened before, so my first impulse is to say, “Sure.  It gets colder in the winter.  Is that news?” 

The new thing is generally thought to be the “Polar vortex.”  I thought we knew about that for a long time.  It’s cold at the pole, air sinks and you get a Coriolis effect.  That means circling air coming in from the outside of where air is sinking or rising (the earth does rotate if memory serves) maintains much of its momentum and traveling in a circle of smaller circumference spins at a greater rate and, since the ground is not circulating as fast as the atmosphere, moves faster than the ground so you get a wind.   I doubt that has changed.  But the prediction was quite good, so I think what has really changed is our understanding of what is going on. 

And low and behold they are blaming the melting of arctic ice.  The pole is warmer, less air is coming in and falling, the vortex decreases in size and power, and “the jet stream shifts north.”  Sure.  Good work lads.  Of course nobody is quite saying that once the arctic ocean melts altogether there will be no vortex and no jet stream at all, and things will be quite different.  But at least they are groping around at the edge of the issue and have concluded that the melting ice cap can drive the weather really wild.

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