Assimilation of TOPEX/Poseidon data into a seasonal forecast system

Abstract

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 oceanatmosphere seasonal forecast system. We estimate the impact that assimilation of sea level might have on the ocean analysis compared to the assimilation of subsurface temperature observations. As a first step satellite-observed sea level anomalies are compared with simulated sea level anomalies from model experiments. To assess the quality of the ocean analysis and the altimeter data further, model results and satellite data are compared to independent sea level observations from tide gauges. Model results are from three experiments: no assimilation, assimilation of subsurface temperature data, and assimilation of sea level data, respectively. The comparison is focused on the equatorial Pacific where subsurface temperatures are frequently sampled and impact of subsurface oceanic conditions on forecast skill is assumed to be large . It is shown that altimeter data assimilation can match subsurface temperature assimilation in this area.