polar vortex

A polar vortex is a large area of low pressure and cold air that surrounds both of Earth's poles. It exists year-round but typically strengthens in the winter and weakens in the summer.

The phenomenon consists of two distinct parts that exist at different levels of the atmosphere:

• Stratospheric Polar Vortex: A band of strong westerly winds that forms in the stratosphere (about 10–30 miles above the surface) during the winter. It helps keep cold air confined to polar regions.
• Tropospheric Polar Vortex: Located in the lower atmosphere (where weather happens), this is the region poleward of the polar jet stream.

How it Affects Weather

While the polar vortex itself is a normal feature of the atmosphere, it can influence winter weather in the mid-latitudes—including the United States, Europe, and Asia—when it becomes disrupted:

• Expansion and Shifting: During winter, the vortex can sometimes weaken or become "wavy". When this happens, the jet stream—which usually acts as a barrier keeping cold air trapped near the poles—can lose its force or shift.
• Cold Air Outbreaks: As the jet stream becomes more erratic, it allows masses of frigid, Arctic air to spill southward out of the polar region. This is often what people are referring to when they hear news reports about a "polar vortex" causing extreme cold in areas that are not usually accustomed to such temperatures.

It is a common misconception to confuse the polar vortex with the polar jet stream. While they interact, the polar vortex is a high-altitude, atmospheric circulation pattern, whereas the jet stream is a current of fast-moving air closer to the Earth's surface that directly influences day-to-day weather patterns.