North Atlantic Syndrome

Any old wind that blows …

Originally posted by Wikipedia:

The North Atlantic oscillation (NAO) is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high. Through east-west oscillation motions of the Icelandic low and the Azores high, it controls the strength and direction of westerly winds and storm tracks across the North Atlantic. It is highly correlated with the Arctic oscillation, as it is a part of it.

The NAO was discovered in the 1920s by Sir Gilbert Walker. Unlike the El NiƱo-Southern Oscillation phenomenon in the Pacific Ocean, the NAO is a largely atmospheric mode. It is one of the most important manifestations of climate fluctuations in the North Atlantic and surrounding humid climates.

The North Atlantic Oscillation is closely related to the Arctic oscillation (AO) but should not be confused with the Atlantic Multidecadal Oscillation (AMO).


The NAO has multiple possible definitions. The easiest to understand are those based on station differences, such as:
Lisbon, Portugal and Stykkisholmur/Reykjavik, Iceland
Ponta Delgada, Azores and Stykkisholmur/Reykjavik, Iceland
Azores (1865-2002), Gibraltar (1821-2007), and Reykjavik, Iceland[1]

These definitions all have in common the same northern point (because this is the only station in the region with a long record), in Iceland; and various southern points. All are attempting to capture the same pattern of variation, by choosing stations in the "eye" of the patterns shown in the graphic.

A more complex definition, only possible with more complete modern records generated by numerical weather prediction, is based on the principal empirical orthogonal function (EOF) of surface pressure.[1] This definition has a high degree of correlation with the station-based definition. This then leads onto a debate as to whether the NAO is distinct from the North American Mesoscale Model (NAM) or AO, and if not, which of the two is to be considered the most physically-based expression of atmospheric structure (as opposed to the one that most clearly falls out of mathematical expression).

Which is all very well if you can understand it.
The trouble with old weather data is that once it has been distributed to the Weather forecast manufacturers for tuning into presentations, the stuff becomes the property of climatology.

And they love averages.
The senior meteorologist having done his best to rid the computer model of averages in the runs he chooses for his prophecies, this seems a dichotomy.

That's because it is:

Originally posted by Wikipedia:

Westerly winds blowing across the Atlantic bring moist air into Europe. In years when westerlies are strong, summers are cool, winters are mild and rain is frequent. If westerlies are suppressed, the temperature is more extreme in summer and winter leading to heatwaves, deep freezes and reduced rainfall.

A permanent low-pressure system over Iceland (the Icelandic Low) and a permanent high-pressure system over the Azores (the Azores High) control the direction and strength of westerly winds into Europe. The relative strengths and positions of these systems vary from year to year and this variation is known as the NAO. A large difference in the pressure at the two stations (a high index year, denoted NAO+) leads to increased westerlies and, consequently, cool summers and mild and wet winters in Central Europe and its Atlantic facade. In contrast, if the index is low (NAO-), westerlies are suppressed, these areas suffer cold winters and storms track southerly toward the Mediterranean Sea. This brings increased storm activity and rainfall to southern Europe and North Africa.

So what do we do with it?

By controlling the position of the Azores high, the NAO also influences the direction of general storm paths for major North Atlantic tropical cyclones: a position of the Azores high farther to the south tends to force storms into the Gulf of Mexico, whereas a northern position allows them to track up the North American Atlantic Coast.

It does more than that:

When the so called anomaly is in the negative phase…. (What a set of unwieldy terms this syndrome encourages.) ….when the so called anomaly is in the negative phase…. as far as I know there is an High pressure area over Greenland.

Since this affects temperatures there -which even with a Low is cold, the area being snowbound more or less all the year through; sea temperatures seem to be greater than in more "normal conditions".

But what IS normal?


3 thoughts on “North Atlantic Syndrome

  1. I'll have to look into this more deeply obviously. But for now there are three or four significant effects to be seen with this syndrome1. World-wide, the lifetime of tropical storms is short when the oscillation is negative. Typically a cyclone in the tropics or subtropics lasts no more than a few days and of course can not get much convergence in that time.2. Those storms that DO develop any significance in the North Atlantic itself, are drawn north east or NNE rather than east or NE.Even tropical storms can end up going into the Arctic rather than crashing on the shores of Norway.3. Flaccid systems generally. When the High persists over Greenland, the whole North Atlantic has low pressure anticyclones and high pressure cyclones. When the High systems DO reach significant pressures, the likelihood for the planet is that a severe tornadic event will take place or that a relatively severe earthquake will occur.The latter point is the more interesting in viwew of the recent Chilean disaster.When the storms of the world broach or reach land, they tend to fall apart. This is as far as I know termed Divergence. The pressure waves that held together when the storm was at sea, go their own separate ways.But in a flaccid system, the storms break up whilst still at sea. Thus earthquakes tend to be less devastating. Until the time comes for the exception to be reached.But why does that happen?

  2. Perhaps the term "less devastating" might have been dropped in favour of "less powerful".The point is that no Mag 6 to 7 quake should kill. Granted there are a huge number of ancient buildings that were never designed to cope with much over a Mag. 4 -if that.But these days it aught to be illegal for any building in a region known for tremors to have less than sound structural properties for dealing with something less than an M 7.And to house children in a public building built on the ugly Staatliches Bauhaus concepts is strikingly bad management amounting to more than the normal dereliction of duty practised in Communist countries.

  3. If this is a standard result, contemporary seismology has a lot to answer:2010/04/275.6 17:17 WESTERN INDIAN-ANTARCTIC RIDGE4.0 15:54 RAT ISLANDS, ALEUTIAN ISLANDS, ALASKA4.9 15:48 RAT ISLANDS, ALEUTIAN ISLANDS, ALASKA4.5 11:04 KURIL ISLANDSThe Rat Islands pair are from a dual divergence. But that is not the point I was going to make:The magnitudes of the quakes increase as the times between them increases. There has to be a "square" law in there somewhere. (Logarithms and all that stuff.)That can't be a standard can it?I mean to say; they'd notice, wouldn't they?

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