What is the polar vortex?
It's not a new weather phenomenon — it's an area of frigid air and low atmospheric pressure that has always existed over each of Earth's poles. But it is making a relatively rare intrusion into the eastern United States, actually the result of warming at the North Pole.
Here’s what you need to know about it:
» It usually strengthens during the winter and can sometimes grow or spill southward. The last dramatic example of that came in 2014, when it repeatedly chilled Maryland with single-digit temperatures. Such outbreaks of Arctic cold also intruded into the United States in 1977, 1982, 1985 and 1989.
» The unusually cold weather it brings doesn’t disprove global warming — it actually serves as more proof that Earth’s climate is changing, scientists say. Last month, air temperatures about 20 miles above the North Pole rapidly rose by about 125 degrees as warmer air flowed in from the south. That warmth split the polar vortex, leaving the pieces to wander, some intruding into parts of Europe and Siberia in eastern Russia.
» Scientists say pieces of the polar vortex are wandering southward more often. A study published year ago in the Bulletin of the American Meteorological Society looked at decades of the Arctic system and found the polar vortex has weakened more frequently in the past, sending columns of frigid air drifting southward.
Baltimore Sun reporter Scott Dance and the Associated Press contributed to this article.