Aeolus Rayleigh-channel winds in cloudy conditions

Aeolus carried the first Doppler wind lidar to measure wind profiles from space. Aeolus was a European Space Agency explorer mission with the objective to retrieve winds data from the collected atmospheric return signal that is the result of Mie and Rayleigh scattering of laser emitted light by atmospheric molecules and particulates. During the course of the mission the quality of Aeolus winds measured in clear-air conditions from Rayleigh-channel-collected data, so called Rayleigh-clear winds, improved substantially. The same is true for winds measured in cloudy and aerosol-rich atmospheric conditions from Mie-channel-collected data, the so-called Mie-cloudy winds. For the latter conditions, good quality winds can in principle also be obtained from Rayleigh-channel-collected data, the so-called Rayleigh-cloudy winds, if contamination of the purely molecular signal by Mie scattering is well addressed. We assess a linear and nonlinear correction for Mie contamination, the latter with the aid of numerical weather prediction model data for determing the correction parameters. We show that the nonlinear correction is able to provide unbiased Rayleigh-cloudy winds. This makes Rayleigh-cloudy winds suitable for use in numerical weather prediction, but also for direct comparison with other wind observations obtained in cloudy conditions, such as atmospheric motion wind vectors.