POLAR VORTEX:
There is a lot of talk about the polar vortex, and its impact on the
current North American cold air outbreak. The Polar Vortex is ring of cold air, stretching out across North America [and another over the Antarctic], which can affect winds closer to the surface [troposphere] and allow Arctic air to spill out.
The polar vortex is a large area, in the stratosphere [± 20 miles high], of constant low pressure, and cold air [-110°F], with a counter-clockwise cyclonic circulation
*, surrounding both of the Earth's poles. It ALWAYS exists near the poles, but weakens in summer, and strengthens in
winter.
*Don’t think tornadoes, or hurricanes, because of the words vortex, & cylcone. It’s not even a storm.
Calling any blast of cold air a polar vortex is wrong. The behaviour of the polar vortex doesn’t just portend colder
weather. It can also foreshadow much warmer
weather. Most of the time the polar vortex has little influence on
winter weather, as it flows like normal, between about 6.2 ➛ 31 miles above the surface.
Often, during winter [in the northern hemisphere], the polar vortex will expand, sending cold air southward, with the jet stream. This occurs fairly regularly during wintertime, and is often associated with large outbreaks of Arctic air in Southern
Canada, and the United States.
When the polar jet stream changes, it affects the movement of weather systems, causing different
parts of the world to see much warmer, or colder, or much wetter, or drier conditions.
When the Arctic polar vortex is especially strong and stable, it encourages the polar jet stream, down in the troposphere, to shift northward. The coldest polar air stays in the Arctic.
When the vortex weakens, shifts, or splits, the polar jet stream often becomes extremely wavy [Arctic Oscillation], allowing warm air to flood into the Arctic, and polar air to sink down into the mid-latitudes.
People often confuse the polar vortex [in stratosphere] with the polar jet stream, but the two are in completely separate layers of the atmosphere. The polar jet stream occurs in the troposphere, at altitudes between 5-9 miles above the surface. It marks the boundary between surface air masses, separating warmer, mid-latitude air and colder, polar air. It’s the polar jet stream that plays such a big role in our day-to-day winter weather, in the mid-latitudes, not the polar vortex.
“Cooking up a stratospheric polar vortex disruption”
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https://www.climate.gov/news-feature...tex-disruption
Climate Variability: Arctic Oscillation
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https://www.climate.gov/news-feature...ic-oscillation