A Teachable Moment: Jet Stream and Weather Whiplash (Look out the Window..)

January 6, 2014

Cornell University:

Cornell’s Charles H. Greene, professor of earth and atmospheric sciences, and Bruce C. Monger, senior research associate in the same department, detail this phenomenon in a paper published in the June issue of the journal Oceanography.

polarvort

Negative Arctic Oscillation conditions are associated with higher pressure in the Arctic and a weakened polar vortex (yellow arrows). A weakened jet stream (black arrows) is characterized by larger-amplitude meanders in its trajectory and a reduction in the wave speed of those meanders.

“Everyone thinks of Arctic climate change as this remote phenomenon that has little effect on our everyday lives,” Greene said. “But what goes on in the Arctic remotely forces our weather patterns here.”

A warmer Earth increases the melting of sea ice during summer, exposing more dark ocean water to incoming sunlight. This causes increased absorption of solar radiation and excess summertime heating of the ocean — further accelerating the ice melt. The excess heat is released to the atmosphere, especially during the autumn, decreasing the temperature and atmospheric pressure gradients between the Arctic and middle latitudes.

A diminished latitudinal pressure gradient is linked to a weakening of the winds associated with the polar vortex and jet stream. Since the polar vortex normally retains the cold Arctic air masses up above the Arctic Circle, its weakening allows the cold air to invade lower latitudes.

anomalies0106

Note Warm anomalies in Alaska, Siberia, Eastern Greenland. click to enlarge

Climate Central:

The cause of the Arctic outbreak can be traced to northeastern Canada and Greenland, where an area of high pressure and relatively mild temperatures is set to block the eastward progression of weather systems, like an offensive lineman protecting the quarterback from the other team.

The atmospheric blocking is forcing a section of the polar vortex to break off and move south, into the U.S. The polar vortex is an area of cold low pressure that typically circulates around the Arctic during the winter, spreading tentacles of cold southward into Europe, Asia, and North America at times. Except this time, it’s not a small section of the vortex, but what one forecaster, Ryan Maue of WeatherBELL Analytics, called “more like the whole enchilada” in a Twitter conversation on Thursday.

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2 Responses to “A Teachable Moment: Jet Stream and Weather Whiplash (Look out the Window..)”

  1. jsam Says:

    Reblogged this on Gra Machree and commented:
    Swathes of North America are icy cold due to a polar vortex. Australia has had its warmest year ever. The globe has just experienced its warmest ever November. And it’s unpleasant in Blighty – deeply so.

  2. HeatherD Says:

    This explains extreme flooding in Colorado & Alberta this year due to “stuck” rainstorms.


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