Assimilation of TOPEX/Poseidon data into a seasonal forecast system

This paper describes first steps towards the quasi-operational assimilation of sea level anomalies from the TOPEX/POSEIDON and ERS1/2 missions into a global ocean model that is used to initialize a coupled ocean-atmosphere se asonal forecast system. We estimate the impact that assimilation of sea lev el might have on the ocean analysis compared to the assimilation of subsurf ace temperature observations. As a first step satellite-observed sea level anomalies are compared with simulated sea level anomalies from model experi ments. To assess the quality of the ocean analysis and the altimeter data f urther, model results and satellite data are compared to independent sea le vel observations from tide gauges. Model results are from three experiments : no assimilation, assimilation of subsurface temperature data, and assimil ation of sea level data, respectively. The comparison is focused on the equ atorial Pacific where subsurface temperatures are frequently sampled and im pact of subsurface oceanic conditions on forecast skill is assumed to be la rge. It is shown that altimeter data assimilation can match subsurface temp erature assimilation in this area. (C) 1999 Elsevier Science Ltd. All right s reserved.