The Contribution of Aeolus Wind Observations to ECMWF Sea Surface Wind Forecasts

Aeolus is the first satellite mission focusing on wind profile detection from near the surface to about 30 km in height on a global scale. This study evaluates the contribution of Aeolus winds to sea surface wind forecasts geographically by further analyzing the Observing System Experiments from the European Centre for Medium-Range Weather Forecasts (ECMWF) with scatterometer winds from the meteorological operational satellites (assimilated into the model) and the Haiyang-2B satellite (not assimilated into the model). The findings indicate that Aeolus has the ability to reduce the root-mean-square difference between scatterometer winds and background forecasts (short-range) by about 0.05%-0.16% on average for climatic regions, except for the meridional wind component in the tropics. Also, Aeolus can generally reduce zonal biases of the background forecasts, while its beneficial impact on meridional biases mainly occurs in the Northern Hemisphere extratropics and tropics. For medium-range forecast assessments, as the forecast step extends up to day 5, the positive impact of Aeolus on sea surface wind forecasts becomes more evident and is even greater than 3%, especially for extratropical ocean regions in the Southern Hemisphere. Furthermore, the impact of Aeolus shows seasonal variation, with a substantial positive impact from September 2019 to February 2020 and a negative impact mainly in March, April, and May 2020. Wind information plays a vital role in understanding atmosphere dynamics and improving weather forecasts. Aeolus is the first satellite to detect global wind profiles from near the surface to about 30 km in height. These wind profiles can be used to assist in Numerical Weather Prediction (NWP). In this study, we investigate whether the Aeolus winds can benefit the sea surface wind forecasts in the global NWP model at ECMWF by exploiting satellite-observed ocean winds. The finding is that Aeolus can generally reduce background forecast (i.e., short-range forecast) biases for the east-west wind component, while the bias reductions for the north-south wind component are mainly found in the Northern Hemisphere extratropics and tropics. Moreover, Aeolus can slightly reduce the difference between satellite observations and forecasts of vector winds for both short-range and medium-range forecasts up to day 5, especially in the Southern Hemisphere extratropics. In addition, the effects of Aeolus on medium-range sea surface wind forecasts vary with season. Generally, Aeolus has a more positive impact between September 2019 and February 2020. However, its impact tends to be negative for many regions during March, April, and May 2020. Aeolus can slightly improve background forecasts in global sea surface vector wind by similar to 0.11% on average Aeolus can slightly reduce zonal and meridional wind biases of background forecasts for most climatic ocean regions As the forecast step extends to day 5, the positive impact of Aeolus becomes more evident and varies with seasons