Ocean Science www.ocean-sci.net 1812-0784 1812-0792 5 2 2009 10.5194/os-5-173-2009 http://www.ocean-sci.net/5/173/2009/ http://www.ocean-sci.net/5/173/2009/os-5-173-2009.html http://www.ocean-sci.net/5/173/2009/os-5-173-2009.pdf 173 190 2009-06-02 Evaluating two numerical advection schemes in HYCOM for eddy-resolving modelling of the Agulhas Current B. C. Backeberg bjorn.backeberg@nersc.no L. Bertino J. A. Johannessen Department of Oceanography, University of Cape Town, South Africa Mohn-Sverdrup Center for Global Ocean Studies and Operational Oceanography, Norway Nansen Environmental and Remote Sensing Center, Norway Geophysical Institute, University of Bergen, Norway A 4th order advection scheme is applied in a nested eddy-resolving Hybrid Coordinate Ocean Model (HYCOM) of the greater Agulhas Current system for the purpose of testing advanced numerics as a means for improving the model simulation for eventual operational implementation. Model validation techniques comparing sea surface height variations, sea level skewness and variogram analyses to satellite altimetry measurements quantify that generally the 4th order advection scheme improves the realism of the model simulation. The most striking improvement over the standard 2nd order momentum advection scheme, is that the southern Agulhas Current is simulated as a well-defined meandering current, rather than a train of successive eddies. A better vertical structure and stronger poleward transports in the Agulhas Current core contribute toward a better southwestward penetration of the current, and its temperature field, implying a stronger Indo-Atlantic inter-ocean exchange. It is found that the transport, and hence this exchange, is sensitive to the occurrences of mesoscale features originating upstream in the Mozambique Channel and southern East Madagascar Current, and that the improved HYCOM simulation is well suited for further studies of these inter-actions. 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