Are ECMWF winds a reliable auxiliary data source for SMOS salinity retrievals over rainy regions?

The European Centre for Medium-range Weather Forecasts (ECMWF) 10-m equivalent neutral wind data are used as auxiliary information in the SMOS operational Level 2 processing to improve the Sea Surface Salinity (SSS) retrievals. Errors in the auxiliary parameters (i.e., SSS climatology, Reynolds SST, and ECMWF wind) are known to propagate onto the SSS estimation in the cost function minimization step. In particular, high wind areas (above 12 m/s), where ECMWF wind uncertainty is higher, are usually flagged in the SSS retrieval. In this post, the ECMWF wind uncertainty under rainy conditions is assessed. It is shown that ECMWF does not well resolve the rain-induced wind variability and as such the wind uncertainty substantially increases in both rainy areas and their vicinity. It is therefore concluded that ECMWF winds should not be used to retrieve SSS under such conditions.

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