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Representation of Nordic Sea overflows in a set of Norwegian Earth System Model (NorESM) experiments
Chuncheng Guo, Mehmet Ilicak, Mats Bentsen, Ilker Fer
Geophysical Institute, University of Bergen and Bjerknes Centre for Climate Research, Bergen, Norway
(Abstract received 09/02/2015 for session X)
ABSTRACT
The water exchange between the Nordic Seas and the North Atlantic plays an important role in modulating water mass properties and the thermocline circulation in the Atlantic. As a common issue, z-coordinate ocean models suffer from spurious numerical mixing that leads to a too light and shallow penetration of overflow product water. In this work we examine the behaviour of Iceland-Scotland Overflow Water (ISOW) and Denmark Strait Overflow Water (DSOW) in NorESM which features a isopycnic coordinate ocean model that originates from MICOM. The four experiments being checked have different forcing (coupled or driven by CORE2 interannual forcing) and different ocean resolutions (one and quarter degrees). T/S properties and layered volume transport (Q) at various key cross-sections in the North Atlantic are shown. Q of DSOW is severely underestimated in the one degree runs (less than a third of observations). Q of ISOW for all the four experiments agrees with observations, however, ISOW does not turn westwards at and south of the Reykjanes Ridge (RR) but carries on flowing southwards. Hence there is a lack of overflow water in the western North Atlantic which favours the production of Labrador Sea Water (LSW). LSW is massive in all the experiments as could be seen from the maps of LSW thickness and mixed layer depth. Two sensitivity experiments with modified bathymetry and enhanced diapycnal mixing east of RR fail to redirect ISOW west of RR.
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2015 LOM Workshop, Copenhagen, Denmark June 2nd - 4th, 2015