GOCE RESEARCH FOR OCEANOGRAPHY IN THE NETHERLANDS Prof. dr. W.P. M. de Ruijter, dr P.J. van Leeuwen, dr ir H.A. Dijkstra Institute for Marine and Atmospheric research Utrecht (IMAU) P.O. Box 80005, 3508 TA Utrecht, Netherlands. w.p.m.deruijter@phys.uu.nl, P.J.vanLeeuwen@phys.uu.nl, H.A.Dijkstra@phys.uu.nl ABSTRACT GOCE-related research in the Netherlands focuses on the dynamics and operation of the thermohaline circulation, the global scale transport of heat and salt (and other water characteristics) by the oceans. This circulation is to a large extend set by several ‘choke points’ where it displays high sensitivity to changing conditions. The key areas that are addressed are the connection between the Indian and the Atlantic Oceans around South Africa and the separation and extension of western boundary currents like the Gulf Stream and the Kuro-Shio. INTRODUCTION The most important missing link in the determination of the absolute velocity field of the ocean circulation is an accurate geoid. TOPEX/POSEIDON and ERS satellite altimeters have been used to determine the geoid for long wavelengths, but for length scales below 1000 km the accuracy is still too small. Large ocean currents like the Gulf Stream, the Kuro-Shio, the Agulhas and the Brazil Current have a strong boundary-layer character. Their characteristic length scales are of the order of tens to one hundred km, so that their time-mean velocity field cannot be determined from altimetry. These large currents transport important quantities of heat, salt and other characteristics of the seawater. The expectation is that the GOCE mission (Gravity Field and Steady State Ocean Circulation Explorer) will provide an accurate geoid on these smaller length scales. From that a time-mean dynamic topography can be derived and thus the absolute velocity field at the ocean surface in those main currents. When the time-mean circulation is known it can be combined with, at that time (2005), about 20 years of time-varying velocity fields from the ongoing altimeter missions (i.e. Geosat, TOPEX/POSEIDON, ERS1 and 2, GFO and JASON). This will provide an enormous extension of the data that can be used to study the interannual and decadal variability of the ocean circulation. The oceanographic community in the Netherlands is hosted by the NIOZ (Netherlands Institute for research of the sea), IMAU (Institute for Marine and Atmospheric research Utrecht) and KNMI (Royal Dutch Meteorological Institute). Over the past ten years, the IMAU oceanography group has developed extensive expertise in the oceanic interpretation of satellite altimetry data, and the assimilation of these data in numerical ocean models. The data handling is carried out in close cooperation with the DEOS group of the TUD. This expertise can now be extended in the direction as indicated here. At the NIOZ, expertise on sea-going physical oceanography is present to provide the necessary validation of current and other fields. The KNMI has a strong modeling group with applications ranging from mesoscale features to global intermediate complexity models. The basis for this research is formed by several coherent research projects and programs within the theme ‘Ocean Circulation and Climate’ conducted at the IMAU, and/or coordinated by IMAU oceanographers. More specifically, this concerns a program in which the exchange between the Indian and the Atlantic Oceans is studied, and a program in which the stability and variability of western boundary currents like the Gulf Stream system is investigated in a fundamental way. In the following section these project and programs are discussed, and the need for the absolute sea-surface height is highlighted. That is followed by a section on the proposed (and ongoing) research. A summary and conclusions sections closes this abstract.