Showing posts with label Polar jet stream. Show all posts
Showing posts with label Polar jet stream. Show all posts

Thursday, December 20, 2012

Polar jet stream appears hugely deformed

World climate zones used to be kept well apart by jet streams. On the northern hemisphere, the polar jet stream was working hard to separate the Tundra and Boreal climate zones' colder air in the north from the Temperate climate and the Subtropical climate zones' warmer air in the south.

NOAA image
The greater the difference in temperature between north and south, the faster the jet streams spin around the globe, the polar jet stream at about 60°N and the subtropical jet stream at about 30°N, as illustrated on above image. 

NOAA image
The polar jet stream used to move at speeds of up to 140 miles per hour, while following a relatively straight track that was meandering only slightly, i.e. with waves that go up and down only a little bit.

Accordingly, the Northern Temperate Zone used to experience only mild differences between summer and winter weather, rather than the extreme hot or cold temperatures that we've experienced recently.

Accelerated warming in the Arctic is decreasing the difference in temperature between the Arctic and the Northern Temperate Zone. This is causing the polar jet to slow down and become more wavy, i.e. with larger loops, as illustrated by the NASA image further below.
Polar jet stream (blue) & subtropical
jet stream (red) - NOAA image

                   Diagram of Doom, Sam Carana
This is a feedback of accelerated warming in the Arctic that reinforces itself. As the jet stream slows down and its waves become more elongated, cold air can leave the Arctic more easily and come down deep into the Northern Temperate Zone. Conversily, more warm air can at the same time move north into the Arctic.

The 'open doors' feedback further decreases the difference in temperature between the Arctic and the Northern Temperate Zone, in turn further slowing down the jet stream and making it more wavy, and thus further accelerating warming in the Arctic.

The polar jet stream can travel at speeds greater than 100 mph. Here, the fastest winds are colored red; slower winds are blue. View animated version here. Credit: NASA/Goddard Space Flight Center
How does this affect temperatures? If we look at the average surface temperature anomalies for the month November 2012, we see huge differences in temperatures. Areas in the East Siberian Sea and in east Siberia registered average surface temperature anomalies for November 2012 of about 10 degrees Celsius, compared with 1951-1980. At the same time, areas in Alaska and Canada have been experiencing anomalies of about -10 degrees Celsius.

This suggests a hugely deformed polar jet stream, as indicated by the contour lines on above image on the right. This is very worrying, as this is only one out of many feedbacks that come with accelerated warming in the Arctic. There are at least ten such feedbacks, as depicted in the diagram below, from the earlier post Diagram of Doom.

       Diagram of Doom, Sam Carana
One of the most frightening feedbacks is the albedo loss in the Arctic. The speed at which changes are taking place can be illustrated with the image below, from the earlier post Big changes in the Arctic within years.

The urgency to act is perhaps best expressed by means of the two images below, which can constitute a fitting end-of-year message if you like to share them further. The image below highlights that Arctic sea ice minimum volume in 2012 was only 19.3% what it was in 1979. The background image, prepared by Wipneus, shows an exponential trend projecting a 2013 minimum of only 2000 cubic km of sea ice, with a margin of error that allows Arctic sea ice to disappear altogether next year, i.e. nine months from now.

Finally, the image below highlights that, in 2012, Arctic sea ice area fell by 83.7% in just 168 days, again illustrating how fast things can eventuate. 

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Earlier posts:
Opening the Doorways to Doom