Exclusive: 'NAO' Weather Affects Europe

Ric's NAO map
The question is: Is NAO oscillating or not?.

'NAO:' Reason for Milder Than Normal Spring?

Paris:- Friday, 27. March 1998:- It is no secret that this magazine has readers who live in California. Less well-known is that they write about the weather they have there. No, they do not write about smog.

They have been writing a lot lately about the impossible behaviour of an infrequent type of winter weather, which has been given a sensationalist name by the popular press: it is called 'El Niño.'

Metropole is in the fortunate position of having access to its own weather experts, or as the British would call them, 'Boffins,' which I believe is a type of penguin.

Because the California reports are coming in from a wide area of that large state, I thought it would be reassuring to readers there to have an expert opinion - so I asked Mr. Norman Barth whether residents of Malibu could expect to be swept out to sea anytime soon; although I'm not aware of any current readers residing there.

Instead of what I was expecting, Mr. Barth sent theA2TV meteo surprising and alarming news that Europe has its own uncharacteristic winter weather system, and it is known by the slightly less reassuring name of 'NAO.'

France 2's TV-weather looks like a heatwave, but it's only 1/10th of a degree.

He also suggested I contact David Stephenson in Toulouse for the true facts about 'NAO' - so that readers readers intending to visit Europe in order to escape the caprices of 'El Niño' would not be stricken by panic on encountering 'NAO' here.

This is Dr. Stephenson's report, received today:

A Rough Guide to the North Atlantic Oscillation

by Dr. David B. Stephenson, climate research scientist

Toulouse:- Friday, 27. March 1998:- For many of the past 15 years, a recurring pressure pattern has resulted in milder than normal winters and springs in Europe.

After El Niño, this pressure pattern is one of the most dominant modes of global climate variability, and is less poetically referred to as the North Atlantic Oscillation (pronounced en-ay-oh).

In a diary which he kept in Greenland during the years 1770-78, the missionary Hans Egede Saabye made the following observation: "In Greenland, all winters are severe, yet they are not alike. TheMadeleine Gely umbrellas, since 1834 Danes have noticed that when the winter in Denmark was severe, as we perceive it, the winter in Greenland in its manner was mild, and conversely."

This temperature see-saw is now known to be a manifestation of the NAO.

If in doubt, get an umbrella at Gely's - on the bd. Saint-Germain, since 1834.

The high index winter/springs of 1989, 1990, and 1995, were caused by a net displacement of air from over the Arctic and Icelandic regions towards the subtropic belt near the Azores and the Iberian peninsula, and had strengthened westerlies over the North Atlantic ocean. Stronger westerlies bring more warm moist air over the European continent and gives rise to milder maritime winters.

The low index winter/springs of 1917, 1936, 1963, and 1969 had weaker mean westerlies over the North Atlantic ocean with corresponding colder than normal European winters.

The strengthened or weakened westerlies over the North Atlantic are also known to play a major role in controlling the oceanic ecosystems and ultimately North Atlantic fish stocks.

After more than 100 years of scientific research, the fundamental mechanisms behind the variability of the North Atlantic Oscillation still remain intriguing mysteries.

Some things are however becoming clearer. For example, it appears that the link between the notorious bad boy of the tropical Pacific, El Niño, and his nordic cousin, the NAO, is relatively weak.

It is also becoming clearer that some of the current day climate models are showing some encouraging ability to make probabilistic forecasts of the NAO a season ahead.

What is not clear is why the NAO has become more positive over the last 30 years and there is some speculation that this may be a sign of human induced global warming. On the other hand, it could merely be natural climate variability controlled by the giant dynamo-like gyres in the North Atlantic ocean.

This question is currently being addressed by analyzing long simulations of the NAO using state-of-the-art climate models running on the world's fastest supercomputers. Because of its climatic importance, the NAO is currently generating intense scientific interest and this will undoubtably lead to further advances in our understanding of this intriguing phenomenon.

What a Relief: No Link Between El Niño and NAO!

Dr. Stephenson's mention of 'giant dynamo-like gyres in the North Atlantic' may sound ominous, so I would like to point out a few fundamentals of European geography.

First off, Toulouse is a lot further away from oceans than Malibu; but it is sandwiched between the Atlantic and the Mediterranean - so there is active weather there even if the city is not in danger of sliding into either body of water. This applies to Paris as well.

In direct reference to NAO, Denmark is of course in Europe, but it is way up north, beyond Schleswig-Holstein. Denmark is a very long way from Greenland and Greenland, as everybody knows, is about as 'green' as a normal refrigerator. If you want to worry about Greenland, it is much closer to Scotland.

The North Atlantic Ocean has specific features not even found in the Pacific. It has the warm Gulf Stream, part of which comes from the Caribbean and it picks up more warmth from Miami, and all of this chugs across the Atlantic and sprays itself at Europe, except for a bit that drifts up - beside Scotland! - and along the coast of Norway where it gets confused in the Arctic Ocean.

Another part of the Gulf Stream pulls clockwise, turning toIle-de-France sky the south around the Azores. Here its name changes to Canaries Current. The lines on my map go from red to blue here, even though it is passing a very red spot of Africa. It keeps going clockwise, gets warmer, and heads west as the North Equatorial Current. This was Columbus' warm autobahn to China.

Springtime 'Ile-de-France' sky, digitally enhanced.

Until quite recently, weather in France was national. If there was any weather outside France, it was highly sketchy. In the last couple of weeks, France 2 TV evening weather has been showing that weather here comes from the Atlantic, mostly. This is welcome news because we can now blame it on foreign sources rather than France 2 TV.

Whether it is good or bad, and it is seldom an extreme of either, it has always been the fault of the so-called 'Azores High.' With this latest information, if the Azores High does not seem to be at fault, we can blame NAO instead.

Although this news is of little use to Metropole's California readers, I would still like to thank Norman Barth for pointing me towards NAO and Dr. Stephenson for providing the information about it. For more 'deep background' about NAO, be sure to check Dr. Stephenson's Web site, by clicking on his name in the byline.

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