There has been a lot of interest in the polar vortex this winter. News agencies around the world have used the phrase to explain the extreme cold weather that has affected Canada and the United States since January 2nd, 2014. However, along with this interest comes some confusion. It begs the questions: what is the polar vortex and why is it in the news?
The Polar Vortex
The polar vortex exists in both hemispheres each year during their respective winters. Its existence is a natural phenomenon caused by the temperature contrast that occurs between the sunlit mid-latitude regions and the dark polar region. This difference in temperature (and the fact that the Earth is rotating) causes a west-to-east circulation of air in the upper atmosphere. The polar vortex exists only in the stratosphere, the region of the atmosphere vertically above the troposphere (typically between 10 and 50 km above the surface of the Earth). The vortex causes an isolation of polar air that tends to intensify the cold temperatures if left undisturbed.
In the Southern Hemisphere, the isolated air tends to remain that way, undisturbed, throughout the winter. The Northern Hemisphere polar vortex is far less stable, often subject to disturbances. Why? The answer is simpler than you might expect: there are different landscapes surrounding the northern and southern polar regions. In the southern polar region, the Antarctic continent is surrounded by ocean while the northern polar region is surrounded by various land masses. These land masses, particularly mountainous regions, present an obstacle for the air circulating around the pole. The obstacle can cause waves to be introduced to the vortex, leading to a disruption in the isolation. Imagine the affect of skipping a rock across a lake. At each skip, the rock causes a disturbance in the water’s natural state.
The Arctic polar vortex began this winter in a typical fashion. However, on January 2, 2014, a disturbance event, known as a sudden stratospheric warming, began. This event caused winds in the stratosphere to reverse direction, becoming easterly north of 60˚N. This change caused the vortex to separate into various pockets that migrated southward. As these pieces of the stratospheric vortex moved across southern Canada and the United States, the cold Arctic air in the troposphere was brought along. The significant temperature contrast between the Arctic air and the mild temperatures in the US caused a strengthening of the storm systems moving across the continent. The strengthening brought record low temperatures, significant snowfall and periods of freezing rain.
Measurements of the Polar Vortex at Eureka
The polar vortex plays a pivotal role in the research we do at PEARL. Its size and form are significant factors to the behaviour of ozone in the Northern Hemisphere due to the chemical reactions that can occur in the vortex. Since its size and shape varies significantly year-to-year, we can measure a variety of atmospheric conditions from Eureka. Long-term monitoring also allows us to discern patterns in the behaviour of the vortex over Eureka. During the 2010-2011 winter, we observed a strong polar vortex that went undisturbed for most of the season. This led to extremely cold temperatures that allowed polar stratospheric clouds to form.
These clouds, composed of frozen water vapour and nitric acid, provide a surface for ozone depletion to occur. In March and April of 2011, we observed the first Arctic ozone hole. Due to the sudden stratospheric warming event that began in January of this year, it is unlikely that significant ozone depletion will be observed this spring.
– Felicia Kolonjari
Ph.D. Candidate, University of Toronto