North Atlantic decadal regimes in a coupled GCM simulation
Raible CC, Luksch U, Fraedrich K, Voss R
CLIMATE DYNAMICS
18 (3-4): 321-330 DEC 2001


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.

KeyWords Plus:
NAO, LOW-FREQUENCY VARIABILITY, SEA-SURFACE TEMPERATURE, GLOBAL CIRCULATION MODEL, INTERDECADAL VARIABILITY, ATMOSPHERIC CIRCULATION, SST ANOMALIES, CLIMATE VARIABILITY

Addresses:
Raible CC, Luksch U, Fraedrich K, Univ Hamburg, Inst Meteorol, Bundesstr 60, Hamburg, Germany
Voss R, Deutsch Klimarechenzentrum, D-20146 Hamburg, Germany

Reprints:
Raible CC, Climate and Environmental Physics, Physics Institute, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland, raible@climate.unibe.ch