caa a22 4500 605474184 CHVBK 20210128100346.0 cr unu---uuuuu 210128e20150101xx s 000 0 eng 10.1007/s00382-014-2176-7 doi (NATIONALLICENCE)springer-10.1007/s00382-014-2176-7 Combined influences of seasonal East Atlantic Pattern and North Atlantic Oscillation to excite Atlantic multidecadal variability in a climate model [Elektronische Daten] [Yohan Ruprich-Robert, Christophe Cassou] The physical processes underlying the internal component of the Atlantic Multidecadal Variability (AMV) are investigated from a 1,000-yr pre-industrial control simulation of the CNRM-CM5 model. The low-frequency fluctuations of the Atlantic Meridional Overturning Circulation (AMOC) are shown to be the main precursor for the model AMV. The full life cycle of AMOC/AMV events relies on a complex time-evolving relationship with both North Atlantic Oscillation (NAO) and East Atlantic Pattern (EAP) that must be considered from a seasonal perspective in order to isolate their action; the ocean is responsible for setting the multidecadal timescale of the fluctuations. AMOC rise leading to a warm phase of AMV is statistically preceded by wintertime NAO+ and EAP+ from ~Lag −40/−20yrs. Associated wind stress anomalies induce an acceleration of the subpolar gyre (SPG) and enhanced northward transport of warm and saline subtropical water. Concurrent positive salinity anomalies occur in the Greenland-Iceland-Norwegian Seas in link to local sea-ice decline; those are advected by the Eastern Greenland Current to the Labrador Sea participating to the progressive densification of the SPG and the intensification of ocean deep convection leading to AMOC strengthening. From ~Lag −10yrs prior an AMOC maximum, opposite relationship is found with the NAO for both summer and winter seasons. Despite negative lags, NAO−at that time is consistent with the atmospheric response through teleconnection to the northward shift/intensification of the Inter Tropical Convergence Zone in link to the ongoing warming of tropical north Atlantic basin due to AMOC rise/AMV build-up. NAO− acts as a positive feedback for the full development of the model AMV through surface fluxes but, at the same time, prepares its termination through negative retroaction on AMOC. Relationship between EAP+ and AMOC is also present in summer from ~Lags −30/+10yrs while winter EAP−is favored around the AMV peak. Based on additional atmospheric-forced experiments, both are interpreted as the local seasonal-dependent atmospheric response to warmer North Atlantic. Finally, advection of fresher water from the tropical basin created by local atmosphere/ocean anomalous circulation on one hand and from the Arctic on the other hand due to large-scale sea ice melting leads to decrease of density in the SPG and contributes terminating the model AMOC/AMV events. All together, the combined effects of NAO and EAP, their intertwined seasonal forcing/forced role upon/by the ocean and the primary role of salinity anomalies associated with oceanic dynamical changes acting as an integrator are responsible in CNRM-CM5 for an irregular and damped mode of variability for AMOC/AMV that takes about 35-40 (15-20) years to build up (dissipate). Springer-Verlag Berlin Heidelberg, 2014 Atlantic Multidecadal Variability (AMV) nationallicence Atlantic Meridional Overturning Circulation (AMOC) nationallicence North Atlantic Oscillation (NAO) nationallicence East Atlantic Pattern (EAP) nationallicence Ocean-atmosphere interactions nationallicence Internal climate variability nationallicence Ruprich-Robert Yohan Climate Modelling and Global Change Team, CERFACS/CNRS, 42 Avenue Gaspard Coriolis, 31057, Toulouse, France aut Cassou Christophe Climate Modelling and Global Change Team, CERFACS/CNRS, 42 Avenue Gaspard Coriolis, 31057, Toulouse, France aut Climate Dynamics Springer Berlin Heidelberg 44/1-2(2015-01-01), 229-253 0930-7575 44:1-2<229 2015 44 382 https://doi.org/10.1007/s00382-014-2176-7 text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 research-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s00382-014-2176-7 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Ruprich-Robert Yohan Climate Modelling and Global Change Team, CERFACS/CNRS, 42 Avenue Gaspard Coriolis, 31057, Toulouse, France aut NATIONALLICENCE 700 1- Cassou Christophe Climate Modelling and Global Change Team, CERFACS/CNRS, 42 Avenue Gaspard Coriolis, 31057, Toulouse, France aut NATIONALLICENCE 773 0- Climate Dynamics Springer Berlin Heidelberg 44/1-2(2015-01-01), 229-253 0930-7575 44:1-2<229 2015 44 382