Abstract
Abstract. We review the procedures and challenges that must be considered when using geoid data derived from the Gravity and steady-state Ocean Circulation Explorer (GOCE) mission in order to constrain the circulation and water mass representation in an ocean general circulation model. It covers the combination of the geoid information with time-mean sea level information derived from satellite altimeter data, to construct a mean dynamic topography (MDT), and considers how this complements the time-varying sea level anomaly, also available from the satellite altimeter. We particularly consider the compatibility of these different fields in their spatial scale content, their temporal representation, and in their error covariances. These considerations are very important when the resulting data are to be used to estimate ocean circulation and its corresponding errors. We describe the further steps needed for assimilating the resulting dynamic topography information into an ocean circulation model using three different operational forecasting and data assimilation systems. We look at methods used for assimilating altimeter anomaly data in the absence of a suitable geoid, and then discuss different approaches which have been tried for assimilating the additional geoid information. We review the problems that have been encountered and the lessons learned in order the help future users. Finally we present some results from the use of GRACE geoid information in the operational oceanography community and discuss the future potential gains that may be obtained from a new GOCE geoid.
Highlights
During the late eighties as satellite altimeter data became available globally over longer periods of time, huge efforts were made in the geodetic community to process global data sets to give joint analyses of geoid and ocean dynamic topography, along with a reduction in satellite orbit errors (Wagner, 1986; Engelis and Knudsen, 1989; Denker and Rapp, 1990; Marsh et al, 1990; Nerem et al, 1990)
We review the procedures and challenges that must be considered when using geoid data derived from the Gravity and steady-state Ocean Circulation Explorer (GOCE) mission in order to constrain the circulation and water mass representation in an ocean general circulation model
The quality of the available data were not sufficient to recover the details of the general ocean circulation, the very large scales (>5000 km) of the dynamic topography could be recovered and compared with the early oceanographic results obtained from hydrographic data, e.g. Levitus and Boyer (1994)
Summary
During the late eighties as satellite altimeter data became available globally over longer periods of time, huge efforts were made in the geodetic community to process global data sets to give joint analyses of geoid and ocean dynamic topography, along with a reduction in satellite orbit errors (Wagner, 1986; Engelis and Knudsen, 1989; Denker and Rapp, 1990; Marsh et al, 1990; Nerem et al, 1990). There is an important new opportunity with the GOCE mission that will for the first time provide error covariance information on the gravity field down to spatial scales of 100 km This will allow the impact and constraints of the new gravity anomalies and geoid information on the estimates of ocean circulation to be rigorously assessed. The paper draws heavily on the experiences from European consortium projects GOCINA, GOCINO and GUT preparing for the GOCE mission, and seeks to highlight the major use cases that have been developed over the last few years It proceeds with discussion of the methods oceanographers use to determine ocean circulation, through assimilation into ocean models. As such the paper should stimulate further cross-disciplinary research in geodesy and oceanography, and trigger interest in the oceanographic community to contribute to the challenging task of validation of the GOCE derived geoid and MDT, both on global and regional scales
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