Comparing the results of a 4D-variational assimilation of satellite and insitu data with WOCE CITHER hydrographic measurements in the tropical Atlantic

TOPEX/POSEIDON and ERS1 sea level anomalies, expendable bathythermograph te mperature profiles, sea surface salinities and satellite sea surface temper atures have been assimilated from November 1992 to October 1994 into a non- linear primitive equation model of the tropical Atlantic Ocean using a 4D-v ariational method. The model is forced monthly by ship winds and climatolog ies of heat and fresh water fluxes. The comparison between the model run bo th with and without assimilation is first analyzed in terms of empirical or thogonal functions, and along particular sections in the basin. The results are then compared with independent hydrological measurements obtained duri ng the World Ocean Circulation Experiment cruise CITHER 1, in the tropical Atlantic Ocean in early 1993. The comparison is improved globally with assi milation. The largest impact or the assimilation appears in the North Equat orial Counter Current and the North Equatorial Current (5 degrees N-15 degr ees N). Sub-surface thermocline motions were not reproduced by the model al one, but, are, clearly depicted in the assimilation results along 7 degrees 30'N and are in good agreement with the CITHER I data. Considerations abou t the assimilation technique, the model and the forcing data sets are also discussed via this independent validation. (C) 2000 Elsevier Science Ltd. A ll rights reserved.