제목: Decadal North Atlantic Climate Variability and Predictability Tapped from the Deep Ocean​​​​​​​​​​​​

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​​​​​​​​​​​​​​​​​​연사: 김후명 박사 (NCAR/IBS)​​​​​​​

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장소: 과학관 B102호​​

Abstract:

​The North Atlantic exhibits pronounced variability on decadal and longer time scales, which has implications for climate and marine biological and chemical fields. The subpolar North Atlantic (SPNA) is also the only region where model initialization gives additional predictability beyond that arising from external forcings on decadal time scales. Yet, its driving mechanisms are still under debate. In this talk, I will first review the proposed mechanisms for the decadal North Atlantic climate variability, then provide lines of evidence that it is most likely driven by ocean thermohaline dynamics. In particular, I will show that the source of its variability and predictability is tapped from the deep ocean. More dense water formation (i.e., North Atlantic Deep Water) generated through intensified surface heat loss in the SPNA increases its volume in the deep ocean, suppressing the sea surface height (SSH) above through the steric effect. When this denser water arrives at the subpolar-subtropical gyre boundary, the enhanced zonal SSH gradient strengthens the cross-gyre circulation of the upper ocean (i.e., North Atlantic Current) via geostrophy, bringing warmer subtropical waters to the SPNA. Thus, the source of the decadal upper ocean heat content variability in the SPNA and its prediction skill comes from the deep ocean with the time scales set by the slow advection of the dense water from the deep-water formation regions to the gyre boundary. The surface expression of this variability, referred to as Atlantic Multidecadal Variability, appears to be an integration of this heat convergence in the SPNA and its atmospheric responses, which are possibly underestimated in the current generation of coupled models due to their coarse resolutions.​