Preprints
https://doi.org/10.5194/amt-2022-331
https://doi.org/10.5194/amt-2022-331
 
20 Dec 2022
20 Dec 2022
Status: this preprint is currently under review for the journal AMT.

Long-term validation of Aeolus L2B wind products at Punta Arenas, Chile and Leipzig, Germany

Holger Baars1, Joshua Walchester1,3, Elizaveta Basharova1,3, Henriette Gebauer1,3, Martin Radenz1, Johannes Bühl1, Boris Barja2, Ulla Wandinger1, and Patric Seifert1 Holger Baars et al.
  • 1Leibniz Institute for Tropospheric Research (TROPOS), Leipzig, Germany
  • 2Atmospheric Research Laboratory, University of Magallanes, Punta Arenas, Chile
  • 3University of Leipzig, Leipzig, Germany

Abstract. Ground-based observations of horizontal winds have been performed in Leipzig (51.12 N, 12.43 E), Germany, and at Punta Arenas (53.35 S, 70.88 W), Chile, in the framework of the German initiative EVAA (Experimental Validation and Assimilation of Aeolus observations) with respect to the validation of the Mie and Rayleigh wind products of Aeolus (L2B data). In Leipzig, at the Leibniz Institute for Tropospheric Research (TROPOS), radiosondes have been launched on each Friday for the Aeolus overpasses (ascending orbit) since mid of May 2019. In Punta Arenas, scanning Doppler cloud radar observations have been performed in the frame of the DACAPO-PESO campaign (dacapo.tropos.de) for more than 3 years from end 2018 until end 2021. We present two case studies and long‐term statistics of the horizontal winds derived with the ground-based reference instruments compared to Aeolus Horizontal Line-of-Sight (HLOS) winds. It was found that the deviation of the Aeolus HLOS winds from the ground-reference is usually of Gaussian shape which allowed the use of the median bias and the scaled median absolute deviation (MAD) for the determination of the systematic and random error of Aeolus wind products, respectively. The case study from August 2020 with impressive atmospheric conditions in Punta Arenas shows that Aeolus is able to also capture strong wind speeds up to more than 100 m/s. The long-term validation has been performed for all product baselines since the change to the second laser (called FM-B) in June 2019 until summer 2022 and also partly for the era of the first laser (FM-A).

The long-term validation showed that the systematic error of the Aeolus wind products could be significantly lowered with the changes introduced into the processing chain (different baselines) during the mission lifetime. While in the early mission phase, systematic errors of more than 2 m/s (absolute values) were observed for both wind types (Mie cloudy and Rayleigh clear), these biases could be reduced with the algorithm improvements, such as the introduction of the correction for temperature fluctuations at the main telescope of Aeolus (M1 temperature correction) with Baseline 09. Hence, since Baseline 10, a significant improvement of the Aeolus data was found leading to a low bias (close to 0 m/s) and nearly similar values for the mid-latitudinal sites on both hemispheres. The random errors for the wind products were first decreasing with increasing baseline but later increasing again due to the performance losses of the Aeolus emitter. However, the systematic error is only slightly affected by this issue, so that one can conclude that the uncertainty introduced by the reduced atmospheric return signal received by Aeolus is mostly affecting the random error.

Even when considering these issues, we can confirm the general validity of Aeolus observations during its lifetime. This proves the general concept of this space explorer mission to perform active wind observations from space.

Holger Baars et al.

Status: open (until 30 Jan 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2022-331', Anonymous Referee #1, 30 Jan 2023 reply

Holger Baars et al.

Holger Baars et al.

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Short summary
In 2018, the Aeolus satellite of the European Space Agency (ESA) was launched to improve weather forecast through global measurements of wind profiles. Given the novel technique onboard, extensive validation efforts have been needed to verify the observations. For this reason, we performed long-term validation measurements in Germany and Chile. We found a significant improvement of the data products due to new algorithm version and can confirm the general validity of Aeolus observations.