Interannual to multidecadal variability and predictability of North Atlantic circulation in a coupled earth system model with parametrized hydraulics

Abstract

Several 1000 yr runs of the University of Victoria Earth System Climate Model (UVic ESCM) with a hydraulically controlled overflow in the Denmark Strait are used to analyse the effects of NAO-like variations of the wind stress localized in the subpolar North Atlantic. The focus is laid on improving the representation of the Atlantic meridional overturning circulation (AMOC), the sea surface temperatures in the Nordic Seas and the sea ice coverage without increasing the resolution of the global model. We show that by implementing hydraulic control in the Denmark Strait Overflow the AMOC can be enhanced at depths between 1000 and 3000m by up to 7 Sverdrup (Sv) towards more realistic values. The stability of the Deep Western Boundary Current is considerably enhanced. The expansion of sea ice into the Nordic Seas in the standard run is pushed back from about 65◦N to 75◦N when hydraulic parametrization is switched on. In this case sea ice variations at 75◦N and Northern Europe air temperatures exhibit a lag of 9 yr to variations in the wind stress curl.