Polar Vertex:

♤ In News:The U.S. is bracing itself for freezing temperatures and snow as a result of part of the polar vortex heading southwards sending temperatures spiralling 10 to 20 degrees below normal.

♤ A polar vortex is a persistent, large-scalecyclone that circles either of the planet's geographical poles. On Earth, the base of the polar vortices are located in the middle and upper troposphere and extend into the stratosphere.

♤ They surround the polar highs and lie in the wake of the polar front. These cold-corelow-pressure areas strengthen in the winter and weaken in the summer due to their dependence upon the temperature differential between the equator and the poles.

♤ Occasionally, this very cold air can get dislodged farther south than normal, leading to cold outbreaks in Canada and the U.S.

♤ The cold air will be accompanied by gusty winds Such cold will raise the risk of hypothermia and frostbite in the North and will make it uncomfortable for some outdoor activities in the South.

♤ Last winter in January 2014,temperatures plunged to life-threatening lows in some places, 60 degrees Fahrenheit below zero (minus 51 degrees Celsius) due to the polar vertex.

♤ The chemistry of the Antarctic polar vortex has created severe ozone depletion. The nitric acid in polar stratospheric clouds reacts with chlorofluorocarbons to form chlorine, which catalyzes the photochemical destruction of ozone. Chlorine concentrations build up during the polar winter, and the consequent ozone destruction is greatest when the sunlight returns in spring.