North Atlantic decadal regimes in a coupled GCM simulation |
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Authors: | C C Raible U Luksch K Fraedrich R Voss |
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Affiliation: | Meteorologisches Institut, Universit?t Hamburg, Germany E-mail: luksch@dkrz.de, DE Deutsches Klimarechenzentrum Bundesstr. 55, D-20146 Hamburg, Germany, DE
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Abstract: | The non-stationarity of the North Atlantic atmosphere-ocean coupling is investigated utilizing a long time integration of
a coupled atmosphere-ocean general circulation model (GCM) and a consistent atmospheric experiment forced by the climatological
sea surface temperature (SST) of the coupled GCM. The temporal behavior of the North Atlantic Oscillation (NAO) is non-stationary
with two different decadal regimes being identified: (a) phases with enhanced (active) low-frequency variability of the NAO
index are characterized by regional modes with a baroclinic Pacific-North America (PNA) and a dominant barotropic North Atlantic pattern; (b) in phases with
reduced (passive) low-frequency variability a global mode connects tropics and midlatitudes. The characteristic space scales are similar in the coupled and the consistent atmospheric
experiment; the time scales of the atmospheric eigenmodes are modified by ocean dynamics. In the active (passive) phase the
corresponding atmospheric mode is reinforced by the North Atlantic (tropical Pacific) SST.
Received: 15 September 2000 / Accepted: 30 March 2001 |
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