What is a polar vortex?

A polar vortex is a system of upper-level winds that circle around one of the poles.  Such circumpolar wind systems exist most of the time at both the North and South Poles, but they can change in strength depending on season and also special atmospheric conditions.  They surround and help to define the coldest regions on earth, and in popular accounts the term polar vortex is often applied to the cold polar air mass itself.  In the northern hemisphere, the arctic polar vortex interacts extensively with the polar jet stream and may affect weather patterns at mid-latitudes.

When the arctic polar vortex is strong, it actually acts to contain the coldest air masses in the polar regions favoring periods of milder winter temperatures in northern North America, Europe and Asia.  When the winds of the polar vortex weaken, however, or interact with high-amplitude wave patterns in the jet stream, the shape of the vortex may become distorted.  It’s circulation pattern around the pole may become increasingly asymmetrical, elongated and, in more extreme cases, may even split into two or more patterns.  When this happens large incursions of arctic air may follow southward pointing lobes of the jet stream into mid-latitudes causing a period of colder than normal winter temperatures.

There is intense interest in whether climate change is affecting the pattern of the polar vortex and winter cold snaps.  Many climate scientists believe that natural variations in the climate system are sufficient to explain the frequency of cold spells in recent years.  Others suggest these weather phenomena could be influenced by climate change due to the ongoing decreases in arctic sea ice and the faster rate of temperature increase in the arctic compared to lower latitudes. This is an area of intense current research and considerable concern.

See also What’s with the Weather posts:

See also these NOAA articles:

NOAA graphics: Wavy polar vortex (left) vs. more typical, compact configuration.

NOAA graphic

Maps show the 500-millibar geopotential height (the altitude where the air pressure is 500 millibars) on January 5, 2014 (left), and in mid-November 2013 (right). The cold air of the polar vortex is purple. Maps by NOAA Climate.gov, based on NCEP Reanalysis data from NOAA ESRL Physical Sciences Division.

Category: Climate Change Q&A

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