Saturday, January 9, 2010

Wrap up warm - Arctic Oscillation Hits

Image: Earth Observatory, NASA. Winter Temperatures and Arctic Oscillation (31st December 2009). This image shows the impact of the negative Arctic Oscillation on land surface temperatures throughout the Northern Hemisphere as observed by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite. Cold Arctic air chilled the land surface at midlatitudes, while Arctic land, such as Greenland and Alaska, was much warmer than usual.

I hope you're wrapped up warm when reading this.

As if the awful flooding of November wasn't enough, we've now been hit with a cold spell to beat all cold spells. Since well before Christmas, Ireland along with many other Northern Hemisphere conuntries have been shivering at often sub-zero temperatures.

The boys and girls at Met Eireann tell us that last month was the coldest December for almost 30 years. Having started off the month mild and wet, the second half of December was characterised by much colder conditions with severe frosts and snow falls in places.

Temperatures were down by around 2 degrees celsius on average everywhere making it the coldest December since 1981. Average temperatures at Cork Airport were down 2.4 degrees. It was the coldest of any month, in fact, since 1986 in some areas.

It wasn't all bad news though. What we missed out on in terms of warmth, we made up for in the fact that it was a relatively dry month and the sunniest December since 2001.

As I write though, a severe weather warning is in place for the next few days. Snowfall of between 5 and 10 cm are forecast for Munster and Leinster during Sunday and Monday.

While its undoubtedly causing hardship - dwindling grit and rock salt stocks will surely lead to more dangerous roads and footpaths- we can thank out lucky stars that we're positively balmy when compared to the inhabitants of the Vostok Research Station in Antarctica.

That's because Vostok currently holds the dubious honour of being the coldest place on the planet. On the 21 July 1983 the station thermometer recorded a bone-chilling -89.2 degrees celsius.

The Russian scientific research station is located close to the South Pole and typically contains 25 scientists in "Summer" when temperatures reach a high of -28 degrees. During their winter, about 13 scientists brave the elements at the station.

Back in the Northern Hemisphere, Ireland isn't the only country experiencing a particularly cold spell. Parts of North America, Asia and our neighbours in Europe are all experiencing heavy snowfall and plummetting temperatures. But what's to blame?

Apparently, its all the result of a phenomenon called Arctic oscillation, where opposing atmospheric pressure patterns surrounding the North Pole shift back and forth and disrupts standard weather patterns in the Northern Hemisphere.

Since the 1960's, there has generally been relatively low pressure over the pole and this has been surrounded by a ring of high pressure, keeping the cold air where it should be - on top of the world.

This year however, the opposite has been true- high pressure over the pole and lower pressure surrounding it, has meant that cold air from the Arctic has moved down over many countries in the Northern Hemisphere - Ireland being one of them.

Nobody really understands what drives these changes in air pressure. John Wallace, Professor of Atmospheric Sciences at the University of Washington thinks of it as a "random thing".

"I don't think we understand any reasons why it goes one way one year and the other way another year" Wallace told the New York Times. One thing scientists seem certain about, is that the phenomenon has nothing to do with global warming.


TomS January 11, 2010 at 4:21 AM  

Let me offer a shaky hypothesis: This "arctic oscillation" now causing us misery results from planet Earth's spin and the centrifugal force caused by it. The cold air mass hovering around the Arctic Ocean grows ever colder and denser as it is held in place by the lighter but more energetic southern warm air mass.

Eventually the cold Arctic air mass becomes too dense. The weak -- but always pulling -- centrifugal force pulls the Arctic air mass like a cohesive blob toward the Equator.

Warm air is displaced and probably forced northward as a result. The Coriolis force sets up clockwise and counter-clockwise motions that we see in these moving air masses.

This winter, possibly due to global warming, the Arctic air mass was held in place longer than normal and created an outstanding "negative" Arctic Oscillation (meaning greater surface pressure and height). When northern hemisphere net warming reached its minimum toward the end of December, there was insufficient energy to hold the Arctic air mass in place.

The centrifugal force of the planet's spin began to pull it. Since it was a denser (and colder) mass than normal, it flowed farther south than usual.

If this might actually be the case, global warming ironically produced this miserable cold spell.

If not, maybe this hypothesis will stir up some comment. Tom Slattery

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