Ocean Science publication on modeling of the Agulhas Current

The TOPAZ/HYCOM model system of the Nansen Center is implemented and in operations for the Indian and Southern Oceans. This model system has been applied for evaluating two numerical advection schemes for eddy-resolving modeling of the Agulhas Current. Bjorn Backberg, Laurent Bertino and Johnny A. Johannessen have recently published their results in Ocean Science.
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.
The figure shows the mean sea surface temperature (SST) for the period 2004-2006 from respectively microwave satellite data, and the HYCOM model using the two published advections schemes.
The publication is available at:

http://www.ocean-sci.net/5/173/2009/

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