An improved Aeolus product is now available: Rayleigh channel winds measured in atmospheric conditions with clouds and/or dense aerosol, known as Rayleigh-cloudy winds.

The improved product was activated on 16 February 2023 and is available via the Aeolus Data Dissemination System.

Rayleigh and Mie explained

Aeolus has been providing high quality wind data for several years. In clean air conditions with no clouds and aerosols thanks to Rayleigh channel measured data (Rayleigh-clear winds), and in cloudy or aerosol conditions via the Mie channel (Mie-cloudy winds).

Aeolus’ ALADIN instrument emits laser light into the atmosphere at a wavelength of 355 nm, in the ultraviolet part of the electromagnetic spectrum.

Part of the emitted light is scattered back to the instrument by atmospheric molecules (Rayleigh scattering) and aerosol particles and cloud droplets (Mie scattering).

The total gathered signal (from molecules and aerosol/cloud particulates) is separated by the instrument. Further processing yields a wind estimate from atmospheric molecules (Rayleigh channel) and aerosol+cloud particulates (Mie channel), which all move with the ambient wind.

Rayleigh-clear winds have already demonstrated a substantial impact on improving weather forecasts when assimilated into numerical weather prediction models.

Impacts have been particularly great over the tropics and oceans throughout the northern and southern Hemisphere, so much so that Aeolus data are now used by major weather forecasting services worldwide.

However, until recently, obtaining high quality Rayleigh channel wind measurements in cloudy conditions had not been successful.

The benefit of Rayleigh-cloudy winds

Now, thanks to work from the Aeolus Data, Innovation, and Science Cluster (DISC), a new method to account for Mie scattering in the detected Rayleigh channel signal has been developed and implemented in the data processing chain.

“A Rayleigh-cloudy wind is independent of a Mie-cloudy wind, measured at about the same location,” explains Sebastian Bley of the Leibniz Institute for Tropical Research (TROPOS). “This means that both winds have added value to weather models.”

The resulting winds are free of biases, with random errors comparable to those of Rayleigh-clear winds.

Gert-Jan Marseille of The Royal Netherlands Meteorological Institute (KNMI), who led the development of the improved product, said, “The quality of Rayleigh-cloudy winds is now at a level that it can be used by numerical weather prediction models to improve their forecasts.”

The next steps aim to demonstrate the added value of Rayleigh-cloudy winds in the presence of already available Mie-cloudy winds.

If any Aeolus users have collocated measurements since 16 February 2023, the team would be very interested to see comparisons against the Rayleigh clear and Rayleigh cloudy wind product. Please get in touch with the Aeolus DISC.