the top by the tropopause, a region of stability where temperature increases with height and which acts somewhat like a lid. Thus when air flows over a mountain range—say, the Rockies—it gets compressed vertically and, as a consequence, tends to spread out horizontally. When a spinning ice skater does as much, by spreading his arms, the conservation of angular momentum slows his spin. An atmospheric column going up a mountain behaves in a similar way and swerves to the south to gain some clockwise spin, which offsets part of the counterclockwise planetary component of its spin.
On the far side of the Rockies, the reverse happens: The air begins to stretch vertically and contract horizontally, becoming most contracted in the horizontal when it reaches the Atlantic. And as with an ice skater pulling in his arms, conservation of angular momentum demands that the air gain counterclockwise spin. It does so by swerving to its left. But having moved to the south after crossing the mountains, it is now at a latitude where the planetary component of its angular moment is less than it was originally. To balance this reduction in angular momentum, the air acquires more counterclockwise spin by curving back around to the north. This first southward and then northward deflection creates a waviness in the generally west-to-east flow of air across North America and far downwind to the east.
Well I’m convinced.
All of which means that we’ve been fed a load of old bull about how the melting Arctic ice cap was going to cover the salty warm water of the Gulf Stream with cold fresh water, which would stop the circulation, which would mean we’d all be living in igloos in a couple of decades time. So now I can relax and enjoy the global warming.
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