Improving Ocean Analyses and Enso Forecasts at Noaa Using the Global Ocean Data Assimilation System and Altimetric Sea Level

Operational forecasts of the El Niño / Southern Oscillation in the tropical Pacific have been carried out at NOAA's National Centers for Environmental Prediction since 1994. The Global Ocean Data Assimilation System, introduced in September 2003, provides initial conditions for the Coupled Forecast System global ocean / atmosphere model. The GODAS system is quasi-global, is based on the GFDL MOM-3 ocean model, is forced by momentum, heat, and fresh water surface fluxes, and utilizes 'synthetic salinity' profiles based on Climatological T/S relationships. Evaluation of GODAS vs. in situ observations reveals that the use of synthetic salinity suppresses sea surface salinity variability, causing errors in surface currents. The model assimilates temperature data from XBTs, profiling Argo floats, and the tropical Pacific TAO moorings. The inclusion of altimetry data in GODAS should improve both the salinity and current fields. This paper discusses the improvement in GODAS with the inclusion of altimetry from both Jason-1 and ENVISAT.