It started in the dying days of January 2014. Temperatures everywhere plummeted, turning the Midwest into frozen tundra and shutting down sunny Florida beaches. Panic gripped the nation, and we attributed every numb finger and sinus infection to a mysterious phenomenon called the polar vortex, without knowing what it really was. Caught in a game of telephone, the term meant different things to different people, and at a certain point, polar vortex became synonymous with "crazy cold."
This week, with residents in the central states from Minnesota to Mississippi staring down early freezing temperatures and preparing for a harsh winter, the question remains, "What is a polar vortex?" Let's try to come up with an answer, and see how the vortex stacks up against other winter phenomena like the blizzard and the meteorological bomb.
What is a polar vortex?
A polar vortex is a large-scale, low-pressure cyclone that hovers near the Earth's geographical poles and can persist for several months. These cyclones form each autumn between the lowest two layers of the Earth's atmosphere due to changing wind patterns and heat transfer in the Arctic. Circling winds around the North Pole increase and rise into the stratosphere, and a pocket of cold air forms. Abnormal wind patterns near a polar vortex can cause its shape and strength to change, which may lead to prolonged subzero temperatures in regions of the United States.
The Northern Hemisphere's Arctic vortices tend to develop mostly in regions of Canada and Russia; the lowest pressure and coldest air they have to offer is located near Baffin Island, Canada and somewhere in northeast Siberia.
A polar vortex often breaks apart somewhere between March and May, signaling the last stages of winter. Due to changes in air pressure, it becomes weaker during the summer and stronger during the winter, and the shape, position and strength of a vortex at any given time are dependent upon a number of factors.
For instance, volcanic eruptions in tropical regions are likely to cause stronger polar vortices, incurring lower temperatures and oftentimes longer, more painful winters. Scientists have, however, determined that a more severe polar vortex with record-breaking temperatures one winter tends to be followed at some point by unusually warm weather for a future season, so fear not!
What causes a polar vortex to shift?
As was the case this past January and in the winter of 1985 Arctic outbreak, unique wind patterns can change the shape of a vortex and cause abnormally cold fronts to be released into the polar jet stream. A vortex swirls counter-clockwise, so this cold air is pushed down farther into the United States, impacting regions that typically do not see freezing temperatures and further burying others. Depending on the strength and duration of the winds, these regions can experience subzero temperatures for several days at a time.
How does a polar vortex compare to other winter phenomena?
A polar vortex is most often discussed in reference to a number of other severe winter happenings, including the blizzard, the nor'easter and the meteorological bomb, which residents in the Northern United States are expecting shortly. To the first, precipitation and strong sustained winds are required to call something a blizzard. So therefore, a polar vortex is not a blizzard.
To the second, a nor'easter is similar to a blizzard in that it is a storm. It often entails hurricane-like winds, blizzard-like snowfall and flooding, and it forms off the Atlantic coast and typically spirals upward toward New England. A nor'easter is not a front of sustained cold air, so a polar vortex is not a nor'easter.
And finally, a meteorological bomb is defined as a rapid deepening or intensifying of an extratropical cyclone first over water and then over land. It is most likely to occur in the Northwest Pacific, the North Atlantic, the Southwest Pacific and the South Atlantic. This occurrence is called a bomb because it happens extremely quickly (within a span of 24 hours), and not over time from a buildup and release of cold air. So, although similar, a polar vortex is not a bomb.
In sum, a polar vortex is a polar vortex. It is its own frightful, floating blob of cold.
The concept of the polar vortex is not a new one. We have experienced these types of conditions in the past, and we will continue to do so. We've only recently begun to better document and give a name to what happens when these churning bursts of frigid weather send us to the store for bread and canned milk. But as we prepare for another blast of cold air descending upon us as a gift from our northern neighbors, at least now we know what to call it.