The frequencies,areas,and depths of Euro-Atlantic cyclones and anticyclones are estimated for different phases of the North Atlantic Oscillation(NAO)from NCEP reanalyses of winters from 1952 to 2000.It is shown that a positive NAO phase,prevalent in recent decades,is accompanied not only by a statistically significant increase in the frequency of cyclones in the North Atlantic(between 55 deg and 75 deg N)and in the southeastern Mediterranean,but also by their intensification.At the same time,the frequency of cyclones(but not their depths)in the North Atlantic midlatitudes(between 35 deg and 55 deg N)and over most of Europe is lower in a positive phase.The frequency of anticyclones in a positive NAO phase increases most strongly in the subtropical gyre between 30 deg and 40 deg N,while their depths and areas increase in the subtropical Atlantic,off the European coast,and over northeastern Europe.The influence of cyclonic activity associated with the NAO on the rate of production of North Atlantic Deep Water and on the meridional heat transport in the coupled ocean-atmosphere system is discussed.
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