USA gripped by Polar Vortex
The United States of America is set to face what is known as a Polar Vortex, a large-scale cyclone located near the North Pole sending freezing air circulating thousands of miles away, promising to bring a winter freeze of unprecedented proportions to over one hundred and fifty million Americans.
The center of the current stratospheric Polar Vortex is located near Baffin Island. Just occasionally, the wind flows reach much farther south than usual, and 2014 promises to witness one of these events, the last of which was in 1985. Such events occur when the jet stream develops meanders in its currents of air and a vortex occurs, with warmer air swirling over the Pole, and polar air spiraling southwards.
Is global warming to blame?
Some scientists claim that a reduced snow cover over the Pole reflects less sunlight and so there is an increase in evaporation, altering the air pressure and changing the temperature at the pole. As the polar vortex weakens, it becomes susceptible to changes or meanders in the west-to-east jet stream (the Polar Night Jet), sending cold air swiveling out over larger-than-normal swathes of the northern hemisphere. Low ozone levels have been identified in recent scientific papers as being present in such occurrences.
The polar vortex reaches up from the troposphere (0 to 10 kilometres in altitude), starting at the tropopause (the frontier between the troposphere and stratosphere, around 12 to 15 km), up into the stratosphere (10 to 50 km), through the stratopause (at 50 km.) and into the mesosphere (50 to 90 km). What happens is that the air inside the vortex comes down in a column from the stratosphere and the mesosphere.
At present sweeping over the Great Lakes, the vortex is expected to cover much of the Eastern USA in the coming days.
Inside the vortex, the temperatures reach around 195Kelvin (minus 80 Celsius and minus 112 Fahrenheit). The wind chill factor could send the ground temperatures to as low as minus 70 Celsius. The duration of the cold blast is expected to be several days, less than a week, and there will be a front of warmer air coming in behind.