Arctic Polar Vortex : A polar vortex is a large pocket of very cold air, typically the coldest air in the Northern Hemisphere, which sits over the polar region during the winter season.The Arctic vortex is elongated in shape, with two centers, one normally located over Baffin Island in Canada and the other over northeast Siberia. Around the North Pole, the Arctic vortex spins counterclockwise with wind speeds of 80 mph, stronger than the jet stream’s normal 70 mph winds. In rare events, when the general flow pattern is amplified (or meridional), the vortex can push farther south as a result of axis interruption, such as during the Winter 1985 Arctic outbreak.
1. There are two polar vortices in the atmosphere of planet Earth, one around the North Pole, and one around the South Pole. Each polar vortex is a persistent, large-scale cyclone, circling the planet’s geographical poles.
2. The bases of the two polar vortices are located in the middle and upper troposphere and extend into the stratosphere. They surround the polar highs and lie in the wake of the polar front. These cold-core low-pressure areas strengthen in the winter and weaken in the summer due to their dependence upon the temperature differential between the equator and the poles.
3. They usually span less than 1,000 kilo meters (620 miles) in diameter within which the air circulates in a counter-clockwise fashion in the Northern Hemisphere, and in a clockwise fashion in the Southern Hemisphere. As with other cyclones, their rotation is caused by the Coriolis effect.
4. A large, powerful high pressure system originating in the Eastern or Western Pacific and stretching to the North Pole is required to displace the pocket of cold air.
5. “These high pressure systems can reach Alaska, but it is not typical to stretch all the way to the North Pole,” The vortex is capable of delivering subzero temperatures to the United States and Canada for several days at a time.
6. When the strong air from the Eastern or Western Pacific weakens and falls apart, the polar vortex will retreat into place near the North Pole.
7. The Northern Hemisphere (Arctic) vortex often contains two low pressure centers, one near Baffin Island, Canada and the other over northeast Siberia. The frigid air can find its way into the United States when the polar vortex is pushed farther south, occasionally reaching southern Canada and the northern Plains, Midwest and northeastern portions of the United States.
8. Within the Antarctic vortex in the Southern Hemisphere a single low pressure zone tends to be located near the edge of the Ross ice shelf near 160 west longitude. When the polar vortex is strong, the Westerlies increase in strength. When the polar cyclone is weak, the general flow pattern across mid-latitudes buckles and significant cold outbreaks occur. Ozone depletion occurs within the polar vortices – particularly over the Southern Hemisphere – reaching a maximum depletion in the spring.
The formation of the polar vortex is primarily influenced by the movement of wind and transfer of heat in the polar region. In the autumn, the circumpolar winds increase in speed, causing the polar vortex to spin up further into the stratosphere and the values of potential vorticity to heighten, forming a coherent air mass: the polar vortex. As the winter comes, the winds around the poles decrease, and the air in the vortex core cools. The movement of the air becomes slow, and the vortex stops growing. Once late winter and early spring approach, heat and wind circulation return, causing the vortex to shrink. During the final warming, or the late winter, large fragments of the vortex air are drawn out into narrow pieces into lower latitudes. In the bottom level of the stratosphere, strong potential vorticity gradients remain, and the majority of air molecules remain confined into December in the Southern Hemisphere and April in the Northern Hemisphere, well after the breakup of the vortex in the mid-stratosphere.
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