Last winter our vocabulary grew to include the term “polar vortex” as unusually cold air descended upon us for what seemed like an eternity. The term polar vortex is not new though; this meteorological term was first coined in 1853 to describe strong winds and cold air masses that circle the polar regions of the globe.
In the Northern Hemisphere, these wind flow in a counterclockwise direction while in the Southern Hemisphere the winds travel clockwise. The polar vortex strengthens in the winter and weakens in the summer due to temperature differentials between the polar regions and the equator.
File photo from last winter show people digging their way out of the many snowstorms that hit the Eastern U.S. (Courtesy photo)
As temperatures decrease in the fall, circumpolar winds increase around the poles, forming a coherent air mass known as the polar vortex. These winds reach about 80 miles per hour, causing this cold air mass to increase in size.
As winter progresses the winds decrease in velocity and the size of the vortex diminishes. The warming of the earth that occurs in the spring and summer cause the vortex to weaken and dissipate. In the Northern Hemisphere the polar vortex begins to decrease sometime between March and May.
When the vortex decreases early in the year, we get an early spring; the later it stays intact, the longer winter’s grasp. On average the polar vortex begins its decline in early April. Sometimes conditions arise that cause the vortex to weaken or get disrupted during the winter. When this occurs, the circulation of the vortex will diminish, causing sections of the masses to splinter off and migrate southward, bringing cold arctic air to the lower 48.
These disruptions are normally caused by warmer air mixing with the vortex in the Atlantic Ocean around Greenland. Two such disruptions happened last year from December 6-10 and in early January. Some meteorologists predict that the polar vortex may weaken again this year and send more cold crisp air southward. Perhaps some new flannel or snow shovel would be a wise investment?
Article by FCFCDB
Nature Notes for 1/4/2015