Polar Vortex

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…

(Please visit, like and share Pro EARTH Crusaders and Landscape Ecology UPOU on Facebook or follow me at http://antonantonio.blogspot.com/)