Validation of Aeolus wind products over the tropical Atlantic using radiosondes

<p>We present results from a cross-Atlantic validation of the Aeolus L2B wind product using radiosondes launched in the framework of the Joint Aeolus Tropical Atlantic Campaign (JATAC). Of the total of 20 profiles corresponding to Aeolus overflights, 11 were launched in August-September 2021 from western Puerto Rico and northern St Croix, coordinated by the University of Oklahoma and Utah respectively, and 9 in September 2021 from the semi-arid Cape Verdean island of Sal, coordinated by the Karlsruhe Institute of Technology (KIT).</p> <p>During this period, Aeolus sampled a complex atmospheric environment with a variety of cloud types associated with the Intertropical Convergence Zone (ITCZ) and the West African Monsoon (WAM), as well as dust aerosol particles emitted from Saharan dust outbreaks. The results show that Aeolus Rayleigh-clear and Mie-cloudy wind products do not significantly depend on the collocation distance and time difference between Aeolus and radiosonde measurement. Nevertheless, the presence of clouds and dust can affect the quality of the Rayleigh-clear measurements by reducing the signal intensity of the backscattered light and with that the signal-to-noise ratio. Outliers with large absolute errors and low error estimates, accounting for less than 5% of the data, affect measurements at all altitudes and under all atmospheric conditions, and their cause remains unknown. Finally, we show the existence of an ascending/descending bias in the Rayleigh-clear channel, visible with respect to both radiosondes and European Centre for Medium-Range Weather Forecasts (ECMWF) model equivalents. The results of this study contribute to a better characterization of Aeolus' wind product in different atmospheric conditions and provide valuable information for further improvement of the wind retrieval algorithm.</p>