POLAR VORTEX
by Antonio C. Antonio
August 27, 2014
There are occurrences in nature that are experienced only in specific
parts of the planet. Take the case of a
polar vortex which is something unheard of in the tropics (a region surrounding
the equator) where the Philippines is located.
Although a polar vortex has no effects whatsoever in the tropical or
torrid zone, some degree of knowledge and information should likewise be
assimilated if we are to understand our environment in general.
What is a polar vortex?
“A polar vortex is a persistent, large-scale cyclone located near either
of a planet’s geographical poles. On
Earth, the polar vortices are located in the middle and upper troposphere and
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 weakens in the summer due to their reliance upon the
temperature differential between the equator and the poles. They usually span less than 1,000 kilometers
in which the air circulates in a counter-clockwise fashion (in the Northern
Hemisphere). As with other cyclones,
their rotation is caused by the Coriolis effect.
The Northern Hemisphere vortex often has two centers, one near Baffin
Island in Canada and the other over northeast Siberia. The Antarctic vortex in the Southern
Hemisphere 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
vortex, particularly over the Southern Hemisphere, and reaches a maximum in the
spring.
Polar cyclones are climatological features that hover near the poles
year-round. The stratospheric polar
vortex develops pole-ward and above the subtropical jet stream. Since polar vortices exist from the
stratosphere downward into the mid-troposphere, a variety of heights/pressure
levels within the atmosphere can be checked for its existence.
Polar vortices are weaker during summer and strongest during winter. Individual vortices can persist for more than
a month. Extratropical cyclones that
occlude and migrate into higher latitudes create cold core lows within the
polar vortex. Volcanic eruptions eruptions
in the tropics lead to a stronger polar vortex during the winter for as
long as two years afterwards. The
strength and position of the cyclone shapes the flow pattern across the
hemisphere of its influence. An index
which is used in the northern hemisphere to gauge its magnitude is the
Arctic oscillation.
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.
The breakup of the polar vortex occurs between middle March to middle
May, the average date being April 10th. This event signifies the transition from
winter to spring, and has impacts on the hydrological cycle, growing seasons of
vegetation, and overall ecosystem productivity. The timing of the transition also influences
differences in sea ice, ozone, air temperature, and cloudiness. Early and late polar breakup episodes have
occurred, due to variations in the stratospheric flow structure and upward
spreading of planetary waves from the troposphere. As a result of increased waves into the vortex,
the vortex experiences higher amounts of heat sooner than the normal warming
period, resulting in a faster season transition from winter to summer. As for late breakups, the waves dismantle the
vortex later than normal, causing a delay in the season transition. The early
breakup years are also characterized with persistence of remnants of the
vortex, while the late breaking years have a quick disappearance of these
remnants. In the early breakup phases, only one warming period occurs from late
February to middle March, contrasting to the two warming periods that the late
breakup phases have in January and March. Zonal mean temperature, wind, and
geopotential height exert varying deviations from their normal values
before and after early breakups, while the deviations remain constant before
and after late breakups. Scientists are connecting a delay in the Arctic vortex
breakup with a reduction of planetary wave activities, few stratospheric sudden
warming events, and depletion of ozone.”
(Wikipedia)
A polar vortex can cause extremely cold weather conditions. The photo with this article gives an idea
what could happen. There are more
information in the Internet on polar vortex.
Just my little thoughts…
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