What’s a Rossby Wave?

In a paper published last week in Proceedings of the National Academy of Sciences, Dim Coumou of Germany’s Potsdam Institute for Climate Impact Research suggests that stalled atmospheric currents related to Rossby waves could have been behind recent droughts and flooding.  Jennifer Francis of Rutgers University’s Institute of Marine and Coastal Sciences has proposed a similar connection between the waves and an increase in extreme weather events (although she points to a slightly different mechanism).  So what are these waves?

Here’s how it works.  The strength of the jet stream depends on the temperature difference between the Arctic and the mid-latitudes.  That differential, however, is lessening, because climate change is warming the Arctic twice as fast as the rest of the planet.  Climatologists call this effect “Arctic amplification,” and it may be weakening the jet stream.

A weak jet stream is a wavy, meandering jet stream.  Think of rivers.  When they are young and fast moving, they plow straight for the sea.  As they age and slow down, their path begins to meander.

A slow, meandering jet stream could lead to more extreme weather events, Rutgers’ Jennifer Francis and her colleagues posit.  That’s because when the jet stream stalls, current weather patterns do, too.  Rather than a few dry days, for example, the western United States could experience weeks or months of drought (like it is now).  Rather than a few days of rain in the East, significant flooding could occur.  And as Francis explains in this video, it could all be tied back to Rossby waves.




What’s a Rossby Wave?