Uncertainties in ECMWF Surface Pressure Fields over the Ocean in Relation to Sea Level Analysis and Modeling

Abstract

Knowledge of atmospheric surface pressure (Pa) over the oceans is important for proper interpretation and modeling of sea level variability. Gridded analyses of Pa fields from the European Centre for Medium-Range Weather Forecasts (ECMWF) have been routinely used for altimeter data processing, but their uncertainties are poorly understood. An attempt is made here to quantify the uncertainties in ECMWF Pa fields over the period 1993?95, coinciding with the early years of the TOPEX/Poseidon altimeter mission, by using similar fields from a different operational analysis, a limited set of island barometer records, and TOPEX/Poseidon sea level data. The analysis presented here suggests that ECMWF error variances are under 3 hPa2 over most of the oceans, with typical values closer to 1 hPa2 or smaller, but with substantially larger errors south of 50°S. The worst signal-to-noise ratios occur in the Tropics, where Pa variance is smallest. Errors are mostly associated with uncertainties in submonthly Pa signals.