The Role of Eddies in the North Atlantic Decadal Variability

Chunxue Yang,Andrea Storto,Alessio Bellucci,Rosalia Santoleri,Clément Bricaud,Marie Drévillon

doi:10.3389/fmars.2022.781788

Abstract

The role of eddies in the North Atlantic decadal variability is investigated in this study by using two ocean reanalyses, including an eddy permitting (or eddy poor) reanalysis with horizontal resolution of 0.25 degree and 75 vertical levels and an eddy resolving (or eddy rich) reanalysis with horizontal resolution of 1/12 degree and 50 vertical levels. The prominent mid-1990s warming and post-2005 cooling trend as part of the North Atlantic decadal variability is well displayed in both reanalyses with no significant difference between them. The main driver of the mid-1990s warming and post-2005 cooling trend is the increase and reduction of the meridional ocean heat transport showing similar patterns in both reanalyses. The relative contribution of the heat transport anomalies from eddies to the total heat transport anomalies is slightly larger in eddy resolving than in eddy permitting ocean reanalysis. However, the total mean ocean meridional heat transport increases by 10% in eddy resolving reanalysis with respect to eddy permitting reanalysis and is mainly due to the associated increase of the mean states (temperature and velocity). Therefore, the increase of eddy population due to the increase of horizontal resolution, found by comparing the two datasets, does not affect the MHT anomalies significantly and, consequently, the North Atlantic decadal variability. It is found that the importance of the model horizontal resolution for the North Atlantic decadal variability depends on the interaction between the eddies (small scale) and the mean state (large scale) at decadal time scales. Although the fast increase of computational power will allow soon for eddy-resolving predictions, the need to use high resolution modeling tools for decadal predictions depends on the importance of initialization methods and the interaction between small scale and large-scale variabilities. This study has pivotal implications for the development of North Atlantic decadal prediction systems.

Highlights

The North Atlantic is an important region displayed with prominent decadal variability phenomena. Robson et al (2016) show that the rapid warming in the mid-1990s and cooling from 2005 to 2016 in the eastern subpolar gyre region (SPG) are part of the decadal variability in the North Atlantic
We investigate the contribution of mesoscale ocean eddies to the Meridional Heat Transport (MHT) variability, which in turn drives the decadal climate changes recently observed in the North Atlantic
In this study we investigate the role of eddies in the North Atlantic decadal variability by using two ocean reanalysis products with different spatial resolutions

Summary

Introduction

The North Atlantic is an important region displayed with prominent decadal variability phenomena. Robson et al (2016) show that the rapid warming in the mid-1990s and cooling from 2005 to 2016 in the eastern subpolar gyre region (SPG) are part of the decadal variability in the North Atlantic. The advection of warm water due to the gyre circulation and the strengthening of the Atlantic Meridional Overturning Circulation (AMOC) accompanied by increasing Meridional Heat Transport (MHT) that results from the change of the NAO are responsible for the mid-1990s rapid warming in the SPG region (Haìtuìn et al, 2005; Bersch et al, 2007; Sarafanov et al, 2008; Robson et al, 2012, 2016; Yeager et al, 2012; Delworth et al, 2016; Yang et al, 2016). There is evidence of significant predictability in the North Atlantic sector displayed by decadal prediction experiments, associated with the use of ocean analyses as initialization products (Matei et al, 2012; Bellucci et al, 2013, 2015; Polkova et al, 2019a,b)

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