Satellite altimetry data assimilation in the OCCAM global ocean model

As part of the European AGORA programme we have been assimilating TOPEX/POSEIDON altimeter data into the Southampton Oceanography Centre's high resolution (1/4 degree, 36 level) global ocean model (OCCAM). The assimilation method used is that of Cooper and Haines, a dynamically based method which conserves water properties on isopycnal surfaces. Results of a one-year, 1993, run of this model, driven by ECMWF 6-hourly winds and assimilating 10-day mapped TOPEX/POSEIDON data are presented. A method to improve the model mean sea level for use in altimeter assimilation is described and implemented in the Gulf Stream and Kuroshio separation regions. Results demonstrate the model's ability to adjust to this new mean sea surface and to also propagate the assimilated altimeter signal realistically in time, an essential characteristic if ocean forecasting is to be attempted.