Characteristics of the Nordic Seas overflows in a set of Norwegian Earth System Model experiments

Chuncheng Guo*, Mehmet Ilicak, Mats Bentsen, Ilker Fer

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Özet

Global ocean models with an isopycnic vertical coordinate are advantageous in representing overflows, as they do not suffer from topography-induced spurious numerical mixing commonly seen in geopotential coordinate models. In this paper, we present a quantitative diagnosis of the Nordic Seas overflows in four configurations of the Norwegian Earth System Model (NorESM) family that features an isopycnic ocean model. For intercomparison, two coupled ocean-sea ice and two fully coupled (atmosphere-land-ocean-sea ice) experiments are considered. Each pair consists of a (non-eddying) 1° and a (eddy-permitting) 1/4° horizontal resolution ocean model. In all experiments, overflow waters remain dense and descend to the deep basins, entraining ambient water en route. Results from the 1/4° pair show similar behavior in the overflows, whereas the 1° pair show distinct differences, including temperature/salinity properties, volume transport (Q), and large scale features such as the strength of the Atlantic Meridional Overturning Circulation (AMOC). The volume transport of the overflows and degree of entrainment are underestimated in the 1° experiments, whereas in the 1/4° experiments, there is a two-fold downstream increase in Q, which matches observations well. In contrast to the 1/4° experiments, the coarse 1° experiments do not capture the inclined isopycnals of the overflows or the western boundary current off the Flemish Cap. In all experiments, the pathway of the Iceland-Scotland Overflow Water is misrepresented: a major fraction of the overflow proceeds southward into the West European Basin, instead of turning westward into the Irminger Sea. This discrepancy is attributed to excessive production of Labrador Sea Water in the model. The mean state and variability of the Nordic Seas overflows have significant consequences on the response of the AMOC, hence their correct representations are of vital importance in global ocean and climate modelling.

Orijinal dilİngilizce
Sayfa (başlangıç-bitiş)112-128
Sayfa sayısı17
DergiOcean Modelling
Hacim104
DOI'lar
Yayın durumuYayınlandı - 1 Ağu 2016
Harici olarak yayınlandıEvet

Bibliyografik not

Publisher Copyright:
© 2016 Elsevier Ltd.

Finansman

Data from the RAPID-WATCH MOC monitoring project are funded by the Natural Environment Research Council and are freely available from www.rapid.ac.uk/rapidmoc . Comments from two anonymous reviewers were greatly appreciated and have helped to improve the manuscript. The present work benefited from the input of Elizabeth Farmer who provided valuable comments and assistance to the writing of the manuscript. This study was funded by the Research Council of Norway through the project Faroe Bank Channel Overflow: Dynamics and Mixing. M. Ilicak was funded by the NFR NORTH project and the Ice2Ice project that has received funding from the European Research Council under the European Community’s Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement no 610055.

FinansörlerFinansör numarası
FP7/2007
NFR
Natural Environment Research Council
European Research Council610055
Seventh Framework Programme
Norges Forskningsråd

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