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Polar Vortex
We have studied tropical and extratropical cyclones.
Here we will study Polar vorex which is a polar cyclone.
It is also called as circumpolar vortex, polar low, polar cyclone.
It is a
Cold;
Upper tropospheric;
Circumpolar;
Low pressure;
Large cyclonic parcel of air [1000 km] (counter-clockwise in the Northern
Hemisphere)
extending till the lower levels of stratosphere [sometimes spans the region from
the surface up to 10–18 km ]
Polar vortex is closely associated with jet streams [Rossby waves].
It is formed mainly in winter and gets weaker in summer.
It surrounds polar highs and lie in the wake of polar front.
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How Polar Vortex slips towards Midlatitudes [breakdown of the polar vortex] [sudden
stratospheric warming] [polar vortex event] [polar vortex cold wave]
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.
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What is it exactly
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 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.
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.
The vortex is capable of delivering subzero temperatures to the United States and
Canada for several days at a time.
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.
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Polar vortex brings cold parcel of air from poles into Southern Canada and North-
Eastern USA.
Ozone hole [ozone depletion at south pole]
Polar votex and ozone depletions are two distinct but related phenomena.
There is a steady decline of about 4% in the total volume of ozone in Earth's
stratosphere.
Much larger decrease in stratospheric ozone is observed around Earth's polar regions.
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Depletion of ozone is due to increase in halocarbons in the atmosphere.
Halogen atoms like chlorine destroy ozone
Photodissociation (under the influence of sunlight) of ozone-depleting substances
(ODS) like halocarbon refrigerants, solvents, propellants, and foam-blowing agents
(CFCs, HCFCs, carbon tetrachloride and trichloroethane, freons, halons) creates free
chlorine atoms that destroy ozone.
Polar Stratospheric Clouds (PSCs)
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Extend from 12 km – 22 km above the surface
They are nacreous clouds.
Nacreous clouds
Nacreous clouds, sometimes called mother-of-pearl clouds, are rare clouds.
They are mostly visible within two hours after sunset or before dawn.
They need the very frigid regions of the lower stratosphere some 15 - 25 km (9 -16
mile) high and well above tropospheric clouds. They are so bright after sunset and
before dawn because at those heights they are still sunlit.
They are seen mostly during winter at high latitudes like Scandinavia, Iceland, Alaska
and Northern Canada. Sometimes, however, they occur as far south as England.
PSCs or nacreous contain water, nitric acid and/or sulfuric acid.
They are formed mainly during the event of polar vertex in winter; more intense at south
pole.
The Cl-catalyzed ozone depletion is dramatically enhanced in the presence of polar
stratospheric clouds (PSCs) [Finally this how polar vortex leads to ozone depletion]
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PSCs convert "reservoir" compounds into reactive free radicals (Cl and ClO).
These free radicals deplete ozone as shown in the animation below.
So PSC accelerate ozone depletion.
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Prelims question: The formation of ozone hole in the Antarctic region has been a cause
of concern. What could be the reason for ozone depletion at poles?
a) Presence of prominent tropospheric turbulence; and inflow of chlorofluorocarbons
b) Presence of prominent polar front and stratospheric Clouds and inflow of
chlorofluorocarbons
c) Absence of polar front and stratospheric clouds; and inflow of methane and
chlorofluorocarbons
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d) Increased temperature at polar region due to global warming
