Intercomparison of wind observations from ESA’s satellite mission Aeolus, ERA5 reanalysis and radiosonde over China
Abstract. The European Space Agency (ESA) Earth Explorer Atmospheric Dynamics Mission Aeolus is the first satellite mission providing wind profile information on a global scale, and its wind products have been released on 12 May 2020. Here we verify and intercompare the wind observations from ESA’s satellite mission Aeolus and the European Centre for Medium-Range Weather Forecasts (ECMWF) fifth generation atmospheric reanalyses (ERA5) with radiosonde (RS) observations over China, to allow a fitting application of Aeolus winds. Aeolus provides wind observations in aerosol-free (referred to as Rayleigh-clear winds) and cloudy atmospheres (Mie-cloudy winds). In terms of Aeolus and RS winds, the correlation coefficient (R) and mean difference of Rayleigh-clear (Mie-cloudy) vs RS winds are 0.94 (0.97) and −0.24 ± 7.01 (0.18 ± 4.42) m/s, respectively. The vertical profiles of wind speed differences between Aeolus and RS winds are similar to each other during ascending and descending orbits. The comparison of ECMWF winds relative to Aeolus winds provides the R and mean difference of Rayleigh-clear (Mie-cloudy) winds, which are 0.95 (0.97) and −0.16 ± 6.78 (−0.21 ± 3.91) m/s, respectively. The Rayleigh-clear and Mie-cloudy winds are very consistent with the ECMWF winds, likely due to the assimilation of Aeolus wind observations into the ECMWF analysis. Moreover, we find that among the results of comparing Aeolus with RS and ECMWF winds, a small difference between Rayleigh-clear winds relative to RS winds is appeared in the height range of 2–3 km during descending orbits. This result may be due to the high vertical velocity during the descending orbits. The mean differences between Rayleigh-clear (Mie-cloudy) winds and RS winds during the ascending and descending orbit phase are −0.07 ± 0.69 (−0.72 ± 1.48) and 0.3 ± 1.25 (0.1 ± 1.32) m/s. These small deviations indicate that the performance of Aeolus wind products may be unaffected by the orbit phase or HLOS wind conditions. In addition, the R and mean difference between ERA5 and RS zonal wind components are 0.97 and −0.46 ± 3.12 m/s, respectively. Overall, the Aeolus winds over China are similar to the RS and ECMWF winds. The findings give us sufficient confidence and information to apply Aeolus wind products in numerical weather prediction in China and in climate change research.
This preprint has been withdrawn.
Boming Liu et al.
Boming Liu et al.
Boming Liu et al.
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The manuscript by Liu et al. reports a validation study of the Aeolus wind product over China in the time frame between April and September 2020. The horizontal line-of-sight (HLOS) wind speeds provided in the Aeolus L2B product are compared against the wind data from radiosondes as well as the ECMWF atmospheric reanalysis ERA5. Based on a statistical analysis, the systematic errors of the Rayleigh-clear and Mie-cloudy winds are determined separately for ascending and descending orbits. The results are compared to those from previous validation studies.
Although the manuscript was resubmitted multiple times, it still contains several inaccuracies and shortcomings. First of all, the structure of the study is not plausible. The Aeolus validation is performed for two different periods, corresponding to different approaches and datasets to be compared with each other (as depicted in Fig. 2). Consequently, there is a multitude of statistical results from the individual cross-comparisons done for the two periods, which are additionally split into ascending and descending orbits. Furthermore, the comparison of the radiosonde and ERA5 zonal winds, which is mixed with the actual validation of the Aeolus wind results in the text and figures, distracts the reader from the main purpose of the work. Hence, for the sake of clarity and concision, it is suggested to perform a consistent investigation of a single period for which all three datasets are available, while focusing on the validation of the Aeolus HLOS winds.
The study periods covered in the analysis are rather short and should be extended to obtain more robust results. Otherwise, the outcome of the work does not go much beyond the results from the authors' previous publication which is based on radio wind profiler data (Atmos. Chem. Phys., 21, 2945–2958, 2021, https://doi.org/10.5194/acp-21-2945-2021).
Also, a very similar study was meanwhile published by Chen et al. in ACP (Atmos. Chem. Phys., 21, 11489–11504, 2021, https://doi.org/10.5194/acp-21-11489-2021) which compares Aeolus winds to radiosonde and ERA5 data in four Chinese regions over the period from July to December 2019 to October 2020. Given the fact that the study by Chen et al. is more comprehensive and scientifically sound than the present manuscript, the latter represents no substantial contribution to the Aeolus validation in terms of applied methods, concepts or investigated data. Moreover, the scientific quality is not sufficient for being published in AMT. Therefore, I recommend to reject the manuscript.
Many aspects are addressed only very briefly and several statements made in the text lack substantiation. In particular, the following points should be considered before potential re-submission of the manuscript: