Ocean surface wind properties of different scatterometer observation types and numerical weather prediction model fields

Abstract

Understanding surface wind divergence is crucial for multiple physical mechanisms such as convection and pressure adjustments. During the entire year 2022 five scatterometer instruments on MetOp-B, MetOp-C, HY-2B, HY-2C and HY-2D satellites were operational at the same time. Taking advantage of this opportunity, this thesis conducts an analysis of the differences in surface wind divergence between observations from the available satellites and the operational IFS model of ECMWF. In addition, comparison between observations of different scatterometers are performed. The analyses focus on the North Atlantic and the Tropical Atlantic regions, where two important phenomena for the surface wind divergence can be found: the Gulf Stream and the ITCZ. Overall, ASCAT observations show more variability and a higher proportion of extreme wind divergence values in comparison with HSCAT. This is particularly noticeable in the ITCZ and Gulf Stream regions, where convergence extremes are more prevalent. These study’s findings indicate that the operational ECMWF model exhibits a greater bias in wind divergence when compared to the ASCAT satellites (MetOp-B and MetOp-C) than with HSCAT satellites (HY-2B, HY-2C and HY-2D). Particularly, on the Tropical Atlantic, significant bias is found on the ITCZ area with ASCAT and HSCAT instruments for the winter and summer months of 2022. Furthermore, the results reveal more consistency between MetOp-B and MetOp-C observations over the Tropical Atlantic than over the North Atlantic. However, the model biases perceived by ASCAT and HSCAT satellites is greater over the Tropical Atlantic than over the North Atlantic. In consequence, it demonstrates that the operational ECMWF model presents a greater bias on the Tropical Atlantic.