Sunday, January 20, 2013

The North/South Movement of the Jet Streams

A study extending from 1979 to 2001 conducted by Cristina Archer and Ken Caldeira of the Carnegie Institution for Science, Department of Global Ecology, shows that the earth’s jet streams are moving toward the poles and also rising in altitude. This north and southward movement of the streams is proceeding at around 120 miles per decade.

Four jet streams exist, so named because they are wind movements at the level where jets normally fly (between 30,000 and 50,000 feet). Each polar stream is matched by a subtropical jet stream. They run west to east. In the region between the two subtropical jets are the north-easterly and the south-easterly trade winds, and the region where they meet, and often cancel one another out, are the horse latitudes.

I could not find a decent illustration of the other side of the image that I’m showing (from Wikipedia), but a look at the deserts of the world (also from Wikipedia here) suggests that the world’s greatest deserts are located in the regions bounded by the polar and subpolar jet streams.

The authors of the report suggest that the movement of the streams to the north and south will cause the tropical belt to grow and that the paths of storm will shift farther north; that second conclusion because the jet streams inhibit the formation of hurricanes—and, moving father away, will inhibit them less. Another important consequence, for us, is that precipitation will lessen in the South and in the Southwest, thus another Dust Bowl may be in the offing.

Archer and Caldeira are continuing their studies and are unprepared to link the broad trends that they’ve observed to Global Warming—although multiple global warming models have predicted that just this would be happening: the jet streams moving north and south. The jet streams are a relatively new discovery, initially noticed after the 1883 volcanic eruption of Krakatao in Indonesia. The streams distributed the ashes of this eruption, and their paths were first noted then and later. For this reason, we do not know how the jet streams moved in the past—and, indeed, whether they moved at all. But it is clear from records in the center of America that dust storms were a standard feature of farm life in the nineteenth century—although the dramatic Dust Bowl events are largely blamed on farmers plowing up the land.

Whatever the causes, something certainly is happening, and measurable. The new pattern of storms and of droughts can be traced to the movement of the streams, but linking those drifts back to human causation is not yet firmly established, only suspected.

Two news accounts that summarize Archer and Caldeira’s findings are here and here. Their own paper, published in Geophysical Reasearch Letters, is only publicly available as an abstract.

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