NOAA In Situ - Satellite Blended Analysis of Sea Surface Salinity: Preliminary Results for 2010 - 2012
[17-Apr-2013] Xie, P., Boyer, T., Bayler, E., Xue, Y., Byrne, D., Reagan, J., Locarnini, R., Sun, F., Joyce, R., and Arun, K.
Presented at the 2013 SMOS-Aquarius Science Workshop
A technique has been developed to produce analyses of sea surface salinity (SSS) over the global ocean through blending information from in situ measurements and satellite retrievals. Three data sets are employed as inputs to the blended analysis: in situ SSS measurements aggregated and quality controlled by NOAA's National Oceanographic Data Center (NODC); and passive microwave (PMW) retrievals from both the Aquarius/SAC-D and SMOS satellites, received and post-processed at NOAA's Center for Satellite Applications and Research (STAR). The in situ SSS measurements used here are mainly from the Argo program, but also include measurements from tropical moored buoys (TAO/TRITON, PIRATA, RAMA), CTDs, and gliders.
The blended analysis comprises two sequential steps. First, the biases in the satellite retrievals are removed through probability distribution function (PDF) matching against temporally / spatially co-located in situ measurements. The blended analysis is then achieved through optimal interpolation (OI), where the analysis for the previous time step is used as the first guess while the in situ measurements and the bias-corrected satellite retrievals are employed as the observations to update the first guess. Cross-validations are conducted by randomly removing in situ SSS measurements and validating the blended analysis against the withheld in situ data. Results show improved accuracy of the blended analysis, compared to the individual inputs, with reduction in bias and random errors over most of the global oceans. However, uncertainty of large magnitude in the blended analysis exists for high-latitude oceans and coastal regions where the in situ networks are sparse and current-generation satellite retrievals have limitations.
The blended monthly SSS analysis, called the NOAA "Blended Analysis of Sea Salinity" (BASS), is constructed for a three year period from 2010 through 2012. Our in situ satellite blended SSS analysis shows good agreements with the NODC in situ - based analysis over most of the tropical and sub-tropical oceans, with large differences observed for high-latitude oceans and along coasts. Combined empirical orthogonal function (EOF) analysis of the SSS from the BASS analysis, precipitation (P) from CMORPH and evaporation (E) from OAFlux reveals global patterns of the co-variability between the SSS and oceanic fresh water flux (E-P) in association with the evolution of the El Niño Southern Oscillation (ENSO).