A record-breaking cold wave has swept through
the US Midwest and is stated to be caused by a polar vortex.
The polar vortex is a large area of low pressure
and cold air surrounding both of the Earth’s poles. The term “vortex” refers to
the counter-clockwise flow of air that helps keep the colder air near the
Polar vortex always exists near the poles, but
weakens in summer and strengthens in winter. In winter, the north polar vortex
sometimes becomes less stable and expands sending cold air southward with the
jet stream. This is called a polar vortex event. Jet streams are a narrow belt
of high altitude (above 12,000 m) westerly winds in the troposphere.