Weather Words: Arctic Oscillation

The Arctic Oscillation, or "AO" for short, describes the periodic strengthening and weakening of the polar vortex.

In this case, the polar vortex is the air mass that rotates around the North Pole, contained by the polar jet stream. For reference, the polar vortex is the fast-moving current above our heads that separates cold, arctic air from milder air from warmer climates.

How Does The AO Affect Our Weather?

The AO has a large influence on our weather, especially during winter. Whenever the AO is in its positive phase, the polar vortex is stronger.

While many would expect a stronger polar vortex to mean more cold and snow, this is not exactly the case. Whenever the polar vortex is stronger, it holds cold, arctic air farther north.

(In Depth: Sudden Stratospheric Warming | Cross-Polar Flow)

When the AO is negative and the polar vortex is weaker, it opens the door for cold, arctic air to spill farther south. While this ensures that cold, arctic air will move into the U.S., most significant cold snaps that occur in the U.S. during winter are tied to a negative AO and a weaker polar vortex.

A weaker polar vortex and negative AO often occur when warm air travels farther to the north, thus weakening the circulation of the polar vortex. A weaker polar vortex can also promote the transport of air over the North Pole from Siberia to North America, promoting even colder temperatures in the U.S.

Hayden Marshall is a meteorologist intern and First-Year-Master’s Student at the Georgia Institute of Technology. He has been following weather content over the past three years as a Storm Spotter and weather enthusiast. He can be found on Instagram and Linkedin.