World Weather Challenger and The Polar Surge

The polar front is an area on the earth located at approximately 60 degrees north and south where warm air circulating from the tropics meets cold air plunging from the poles. The difference in temperature of these masses of air causes the warm air to rise and most of this moves back towards the equator and sinks at around 30 degrees north and south, adding to the high pressure systems at these latitudes.

The rest of the air that rises at the polar front continues to move towards the poles and as it cools it sinks and returns back towards 60 degrees north and south. However these flows of air do not move in a direct north-south route. They are altered by the rotation of the earth. This rotation will cause any freely moving object to appear to move to the right of the direction of motion in the northern hemisphere and to the left in the southern. This is known as the Coriolis Effect and explains why winds travel clockwise around high pressure systems in the northern hemisphere and anti-clockwise in the southern, with low pressure winds travelling in the opposite direction.

Jet Streams are formed at high altitudes where warm and cold air masses meet. Therefore the polar jet stream is located at 60 degrees north and south approximately along the polar front. During winter when the temperature difference is at its greatest the jet streams will shift towards the equator, and during summer move back towards the poles.

A satellite view of the North Pole shows clouds carried from west to east around the rim of the Arctic by the polar jet stream. This ring of clouds will fluctuate north and south depending on the pressure variances of the polar front below. However trapped inside this loop of clouds is the cold and clear air that sits over the arctic ice. This huge volume of air is very stable and has a key role in dictating the weather further to the south. It is an air mass and with the long cold winter darkness and the extreme cooling caused by the ice beneath, this air mass becomes ever more stable and progressively colder. The air mass has now formed a huge high pressure dome over the arctic which remains until a change in the jet stream causes part of this mass to slide southwards.

Over the North American continent there is nothing to stop the southerly movement of this extremely cold air as there is nothing but flat, open land. This movement south is known as a polar surge. This blast of icy cold air is huge and over North America can reach as far south as Florida and Texas, devastating crops and freezing land sometimes overnight. In 1983-84 a polar surge left almost 90 percent of the USA covered in cold air for nearly two months. In Utah a record low temperature of -54 degrees C (-65 degrees F) was measured.

Unfortunately it was a polar surge in 1986 that caused the destruction of the space shuttle ‘Challenger’. On the morning of 28th January 1986 large quantities of ice coated the launch pad at Cape Canaveral. NASA decided to go ahead with the launch despite the warnings from the manufacturers of the solid rocket boosters that the ‘O’ rings might not perform their function of sealing possible fuel links at such cold temperatures. Sadly the engineers were proved right as the world watched Challenger explode shortly after lift off.
Mark Boardman BSc dip.hyp is a leading author and expert on World Weather. For more information about the world's weather extremes, feel free to visit this site.