Monitoring of Global Sea-Surface Salinity through Combined Use of Satellite Observations and In Situ Measurements

Abstract:

A package of observation-based analyses of pentad (5-day) mean oceanic surface state is developed at NOAA Climate Prediction Center (CPC) to monitor the intra-seasonal variations of sea-surface salinity (SSS) and associated fresh water fluxes (precipitation and evaporation). The pentad SSS analysis is constructed through blending in situ measurements from the NOAA National Center for Environmental Information (NCEI) with satellite retrievals from the European Space Agency’s (ESA) Soil Moisture - Ocean Salinity (SMOS) mission, the joint U.S. and Argentinian Aquarius mission, and the National Aeronautics and Space Administration’s (NASA) Soil Moisture Active-Passive (SMAP) mission. The blended SSS analysis, called Blended Analysis of Sea-surface Salinity (BASS), is produced in two steps, first removing the bias in the satellite data through Probability Density Function (PDF) matching against collocated in situ measurements to ensure quantitative consistency among the retrievals from the three satellites and with the in situ measurements. These bias-corrected satellite SSS retrievals are then blended with the in situ measurements through an Optimal Interpolation (OI) method to achieve best possible quality for the final gridded analysis.

At the meantime, the CPC morphing technique (CMORPH) satellite precipitation estimates and bias-adjusted NOAA Climate Forecast System Reanalysis (CFSR) evaporation values are utilized to quantify the freshwater flux associated with the SSS variations. The bias in the original CFSR evaporation is corrected through comparison with observation-based Objectively Analyzed air-sea Fluxes (OAFlux). The routine monitoring of global ocean SSS and fresh water flux is conducted for monthly, as well as pentad, periods. Anomaly and tendency fields are examined and possible causes of SSS changes are discussed as part of the monitoring package. Detailed results will be reported at the conference.