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What impact does 'El Nino' have on the weather over Europe?

The 'El Nino' phenomenon, or more strictly the warm El Nino -Southern Oscillation (ENSO) event is coupled closely to remarkable shifts in weather patterns in the immediate Pacific basin, and adjacent areas: e.g. parts of North America. For example, it is clear that the altered distribution of warm/cold water across the equatorial Pacific is the primary reason why excessive rain can fall in places like Peru, and a general deficit of rainfall is experienced in Indonesia, parts of Australia and the Philippines. There is also a generally accepted link between a less-than-'normally' active Atlantic hurricane season and the notably warm event that characterises what has come to be called, THE El Nino.

It is becoming clear from recent studies that we can now rule out the 'No Effect' case: this leaves us with two options -

(a) There IS an effect, but it is on a scale that is dwarfed by regional variations closer to home, e.g. long-term thermal inertia in SST distribution in the N. Atlantic, or continental/oceanic temperature differences across the North America - North Atlantic - Eurasian 'super-region'.
(b) There is a direct, and marked effect that leads to verifiable modification of the weather types across the NE Atlantic/European - Mediterranean region.

(a) appears to be the most likely if we take the year overall; indeed, even in studies published which set out to prove the link between warm/cold ENSO regimes, and impacts over Europe, caution is always advised relating to local/regional scale modification.

(b) is climbing higher in the 'probability' stakes, at least if the 'winter' season only is considered. There are an increasing number of studies published that show a direct link between a warm ENSO season, and, for example, altered rainfall/temperature anomalies across west/central Europe. No lesser person than J.Bjerknes postulated in 1966 that altered activity in the equatorial Pacific appeared to significantly alter the strength/orientation of the PFJ over and downwind of the NE Pacific, which in turn must have at least some effect on the long-wave structure downstream. This appears to have been accepted in later studies & developed further using datasets going back over two centuries or more.

However, this topic will be kept under review, as will this Q/A, and our ideas may change ... for the moment though, for more on El Nino/ENSO etc., see the following sites:

[WMO home page]
http://www.wmo.ch/

[El Nino theme page sponsored by NOAA/TOGA-TAO]
http://www.pmel.noaa.gov/toga-tao/el-nino/nino-home.html

... and of course, a search of the WWW will throw up many active sites dealing with El Nino.

In addition, on this site there is set out in summary format some of the arguments/references that subscribers to uk.sci.weather asked for. See it here.