By combining satellite observations and model reanalysis winds, a global data set with higher temporal and spatial resolution ocean surface wind fields can be generated. These superior surface wind fields can have various applications, such as wind forcing of ocean models. The Royal Netherlands Meteorological Institute (KNMI) is responsible for the delivery of two different global data sets of combined surface winds, referred to as IFREMER and ERA5*. IFREMER’s approach focuses on satellite scatterometer observations which are complemented with model reanalysis winds (ERA5). On the other hand, ERA5* is based on ERA5 model reanalysis and corrected with scatterometer observations. The aim of this research is to evaluate global IFREMER and ERA5* surface winds in terms of spatial and temporal characteristics.

In order to validate the surface winds of IFREMER and ERA5*, a reference system of true winds is required. For this, quality-controlled wind observations from an independent Chinese scatterometer Haiyang-2B have been used. This comparison study has been carried out for the year 2019 focusing on zonal wind, meridional wind and wind speed. IFREMER and ERA5* wind fields have been collocated in time and space to HY-2B wind observations using a 6-hour and 1-hour window respectively. This methodology was applied to overcome differences between the data sets in grid definition, wind representation, spatial resolution and temporal resolution.

On a global scale, IFREMER shows larger average and standard deviation of wind differences with respect to HY-2B than ERA5*, specifically in coastal regions and at higher latitudes. The results of this research suggest that the ERA5* wind product generates more accurate surface ocean winds than IFREMER, except for in the tropics, assuming that HY-2B winds represent the true value. Moreover,
at higher wind speeds both global wind products underestimate HY-2B wind, whereby IFREMER already deviates at lower winds than ERA5*. The IFREMER winds showed suspicious satellite tracks and temporal wind inaccuracies, most likely as a result of its 6-hourly resolution. It is recommended that a follow-up investigation is carried out with validation of buoy data in the tropics to investigate the underlying causes of the observed local wind bias.