Das Projekt "Meridional Overturning Exchange with the Nordic Seas (MOEN) - WP4: Modelling" wird vom Umweltbundesamt gefördert und von Universität Hamburg, Zentrum für Meeres- und Klimaforschung, Institut für Meereskunde (IfM) durchgeführt. Backgrond: The mild climate of north western Europe is, to a large extent, governed by the influx of warm Atlantic water to the Nordic Seas. Model simulations predict that this influx and the return of flow of cold deep water to the Atlantic may weaken as a consequence of global warming. MOEN will assess the effect of anthropogenic climate change on the Meridional Overturning Circulation by monitoring the flux exchanges between the North Atlantic and the Nordic Seas and by assessing its present and past variability in relation to the atmospheric and thermohaline forcing. This information will be used to improve predictions of regional and global climate changes. MOEN is a self-contained project of the intercontinental Arctic-Subarctic Ocean Flux (ASOF) Array for European Climate project, which aims at monitoring and understanding the oceanic fluxes of heat, salt and freshwater at high northern latitudes and their effect on global ocean circulation and climate. MOEN will contribute to a better long-term observing system to monitor the exchanges between the North Atlantic and the Nordic Seas from direct and continuous measurements in order to allow an assessment of the effect of anthropogenic climate change on the Meridional Overturning Circulation. This we will be done by measuring and modelling fluxes and characteristics of total Atlantic inflow to the Nordic Seas and of the Iceland-Scotland component of the overflow from the Nordic Seas to the Atlantic. General objectives: To contribute to a better long-term observing system to monitor the exchanges between the North Atlantic and the Nordic Seas. To assess the effect of anthropogenic climate change on the Meridional Overturning Circulation. Modelling objectives (WP4, IfM): To model the flow field, the temperature and salinity distribution and the heat fluxes for an area focused on the Iceland-Faroe Ridge, the Faroe Bank and Faroe-Shetland Channel and Wyville-Thomson Ridge. To model long term variations of the locally induced and far field circulation and T/S distribution in order to understand climate variations.
Das Projekt "Impact of physically relevant and numerically induced diapycnal mixing and meso-scale dissipation on meridional mass and tracer transports in the Southern Ocean" wird vom Umweltbundesamt gefördert und von Leibniz-Institut für Ostseeforschung durchgeführt. The Meridional Overturning Circulation (MOC) in the Southern Ocean (SO) is composed of two limbs, the Upper Circumpolar Deep Water (UCDW) flows polewards and upwards across the Antarctic Circumpolar Current (ACC), upwells to the surface at the poleward flank of the ACC and then returns equatorwards as a near surface current. This upper limb is known to be largely adiabatic. In contrast to that, the lower limb of the MOC formed by the Lower Circumpolar Deep Water (LCDW) upwells closer to Antarctica, cools down substantially near the surface and convects down at high turbulent mixing to form the Antarctic Bottom Water (AABW). While the adiabatic upper limb is driven by an imbalance of a northward Ekman transport and an opposing meso-scale eddy transport, the dynamics of the lower limb is more complex due to the additional significance of diapycnal mixing. Thus, a good quantification of these dynamics requires a correct representation of both small-scale (diapycnal) and meso-scale (lateral) eddy mixing. On the other hand, it has long been known that in particular in the SO, large numerical mixing and dissipation in ocean circulation models due to the discretisation of the advection terms obscures the representation of diapycnal mixing and thus strongly limits the predictability of ocean models. It is therefore the aim of this project to use and to further develop a novel analysis tools for numerical mixing and dissipation to quantify effective mixing and dissipation, given by the sum of explicitly parameterised and numerically induced values. By estimating realistic effective mixing and dissipation rates, using our combined expertise of numerical mathematics and small-scale turbulence parameterisation and large-scale high-resolution modelling, we are able to the first time to assess the sensitivity of realistic models of the SO to diapycnal mixing and numerical dissipation and to understand the interplay between meso-scale (lateral) and small-scale (diapycnal) eddy mixing on the lower limb of the MOC.