What does the term "polar vortex" refer to?

The term "polar vortex" refers to a large area of low pressure and cold air surrounding the poles, particularly in the stratosphere. This phenomenon is characterized by a strong, persistent circulation of cold air that typically remains concentrated over the polar regions during the winter months. The polar vortex can influence weather patterns, leading to the potential for colder temperatures and increased storminess in mid-latitude regions when it becomes unstable or disrupted.

This option correctly captures the essence of the polar vortex, as it emphasizes the role of low pressure and cold air, which are central to its definition. The dynamics of the polar vortex are important for understanding seasonal weather patterns and the potential for extreme cold events in other areas as the cold air can occasionally break away from the polar regions.