Ambiguity Removal using different background wind fields

In this report, we compare the OSI SAF SeaWinds 100-km wind products which are made using NCEP background winds, with those using ECMWF background winds. NWP winds are used in the ambiguity removal step of the wind processing, but the influence of the background wind field used should be small, i.e., the selected wind solutions should not depend too much on the quality of the used wind field. Hence, the purpose of this study is to show that the use of ECMWF winds has a small influence on the product quality. Moreover, when there is an influence, it should be an improvement.

The results indicate that the use of ECMWF model winds in the ambiguity removal has a small but distinct positive impact on the product quality, especially in terms of the number of times when the VAR QC flag is set. Moreover, the ECMWF-based 2D-VAR provides slightly better ranking statistics. This provides sufficient justification to use the ECMWF model winds in the pre-operational OSI SAF products.