The Dependence of Short-range Ocean Forecasts on Satellite Altimetry

Short-range ocean forecast and reanalysis systems routinely combine observations from satellite altimetry, satellite sea surface temperature (SST), and in situ temperature and salinity, to initialise global and regional ocean models. The most critical observation type for eddy-resolving applications is arguably satellite altimetry. To quantify the impact of satellite altimetry observations on a data assimilating ocean general circulation model we perform a series of Observing System Experiments (OSEs). We perform four OSEs that all assimilate in situ temperature and salinity observations and satellite SST observations. Different OSEs assimilate data from a different number of altimeters, including an OSE using no altimetry data, and data from one, two, and three altimeters. We show that the neglect of altimetry from a data assimilating model increases the model-observation mis-fits in high-variability regions by almost 40%.