Is our recent strange weather across much of the Northern Hemisphere a sign of things to come?
The Environmental News Network reports that with record storms in Europe; record drought in California; record heat in parts of the Arctic, including Alaska and parts of Scandinavia; but record freezes too, as polar air blew south over Canada and the U.S., causing near-record ice cover on the Great Lakes, sending the mercury as low as minus 50 degrees Celsius in Minnesota, and bringing sharp chills to Texas, everyone is blaming the jet stream.
The U.K. Met Office, which keeps a global weather watch, said in a report put out in mid-February that we are experiencing a “hemispheric pattern of severe weather,” and that the events are linked. The most extreme days of the U.S. cold event, for instance, coincided with some of the most intense storms over the U.K. And physically the connection is through the polar jet stream.
The polar jet stream is a narrow stream of fast wind circling the globe from west to east at the top of the troposphere from 7 to 12 kilometres up and usually between 50 and 70 degrees north. It forms where cold, dense air from the Arctic meets warmer and less dense air from mid-latitudes. At the boundary, winds rush in to equalize the pressure difference. The earth’s rotation diverts these winds to travel eastward.
As the jet roars around the world, it drags weather systems with it. Most of Europe’s weather rides in under the jet stream from the Atlantic, and most of the western U.S.’s weather comes from the Pacific in a similar manner.