Intercomparison of wind observations from ESA&rsquo;s satellite mission Aeolus, ERA5 reanalysis and radiosonde over China

Liu, Boming; Guo, Jianping; Gong, Wei; Zhang, Yong; Shi, Lijuan; Ma, Yingying; Li, Jian; Guo, Xiaoran; Stoffelen, Ad; de Leeuw, Gerrit; Xu, Xiaofeng

doi:https://doi.org/10.5194/amt-2022-26

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https://doi.org/10.5194/amt-2022-26

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26 Jan 2022

| 26 Jan 2022

Status: this preprint was under review for the journal AMT. A final paper is not foreseen.

Intercomparison of wind observations from ESA’s satellite mission Aeolus, ERA5 reanalysis and radiosonde over China

Boming Liu, Jianping Guo, Wei Gong, Yong Zhang, Lijuan Shi, Yingying Ma, Jian Li, Xiaoran Guo, Ad Stoffelen, Gerrit de Leeuw, and Xiaofeng Xu

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.

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Received: 17 Jan 2022 – Discussion started: 26 Jan 2022

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Boming Liu, Jianping Guo, Wei Gong, Yong Zhang, Lijuan Shi, Yingying Ma, Jian Li, Xiaoran Guo, Ad Stoffelen, Gerrit de Leeuw, and Xiaofeng Xu

Interactive discussion

Status: closed

RC1:
'Comment on amt-2022-26', Anonymous Referee #1, 25 Feb 2022
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.

General comments:

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:

In Sect. 2.1, the telescope temperature correction is mentioned without providing references. I propose citing the following articles which describe the correction scheme and its impact on the Aeolus data quality:

Weiler, F., Rennie, M., Kanitz, T., Isaksen, L., Checa, E., Kloe, J. D., Okunde, N., and Reitebuch, O.: Correction of wind bias for the lidar on-board Aeolus using telescope temperatures, Atmos. Meas. Tech. 14, 7167–7185, https://doi.org/10.5194/amt-14-7167-2021, 2021.

Rennie, M. P., Isaksen, L., Weiler, F., Kloe, J., Kanitz, T., and Reitebuch, O.: The impact of Aeolus wind retrievals in ECMWF global weather forecasts, Q. J. R. Meteorol. Soc., https://doi.org/10.1002/qj.4142, 2021.

The authors should clarify what is meant by “It should give only a small quality improvement for Aeolus wind products” (p.5, l. 12) – the change in the update rate of the AUX_TEL or the implementation of the telescope temperature correction? Both measures have improved the global average wind bias, while the latter one had a much higher impact.

The information on the deployed radiosondes provided in Sect. 2.2 is too sparse to evaluate the validation capabilities of the acquired wind data used for the comparisons. In particular, the authors should add details on the vertical resolution and accuracy.

The authors often use the term “similar” when discussing the results of the wind comparisons, particularly in Sect. 3.3. These qualitative statements should be substantiated with numbers. In this context, Fig. 8 is also only of qualitative nature and does not allow conclusions to be drawn. I suggest to plot the wind speed differences versus latitude instead.

Page 15, l. 16: The mean difference of the Rayleigh-clear winds compared to the radiosondes should read “0.19±0.71 (0.13±1.01) m/s” in accordance with Fig. S7.

I strongly suggest to add a summarizing table which provides an overview of the statistical results from the comparisons of the different datasets, periods, ascending/descending orbits.

In Sect. 4, the authors compare their results with previous studies which reported much higher systematic errors of the Rayleigh-clear and Mie-cloudy winds. However, an explanation for these discrepancies is not given. The authors should consider that previous studies were based on preliminary Aeolus data, whereas they validated re-processed data from baseline 10 which, most importantly, includes the telescope temperature correction which strongly reduces the wind biases. This should be clarified.
Citation: https://doi.org/10.5194/amt-2022-26-RC1
RC2: 'Comment on amt-2022-26', Anonymous Referee #2, 28 Feb 2022

“Intercomparison of wind observations from ESA’s satellite mission Aeolus, ERA5 reanalysis and radiosonde over China”, by Boming Liu, Jianping Guo, Wei Gong, Yong Zhang, Lijuan Shi, Yingying Ma, Jian Li, Xiaoran Guo, Ad Stoffelen, Gerrit de Leeuw, and Xiaofeng Xu, Atmos. Meas.Tech. Discuss., https://doi.org/10.5194/amt-2022-26-RC1, 2022

This manuscript describes a validation study that is relevant to Atmospheric Measurement Techniques in the topic of Aeolus L2B wind product over China. The authors describe a statistical intercomparison analysis between the Aeolus L2B wind product and wind data provided by radiosondes and ERA5 model over China.

General comment

The authors used two different periods to compare wind data obtained from the Aeolus L2B wind product with those by radiosondes and ERA5: from 20 April to30 September for radiosondes and from 9 July to 30 September for ERA5 model. The manuscript is not well-structured. The dataset is not suited for discussions of the statistical comparison. The manuscript has not been revised sufficiently in the methodology for the statistical comparison after the submission to ACP. Compared to the manuscript submitted to ACP, the manuscript states opposite results regarding to comparison between Aeolus L2B wind product (Rayleigh-clear) and wind observed by radiosondes or the wind speed differences for radiosonde and ERA5 zonal winds. There are explanation sentences for Figures S1 through S7. However, the figures and reference paper are not shown in the manuscript. The manuscript significantly lacks of the scientific quality and reliability.

Chen et al. have already published a very similar paper using ERA5 and radiosondes over China based on different months (July to December 2019 and May to October 2020). Compared to this manuscript, their manuscript is clearly structured, and all used methodologies are well explained. The manuscript does not extend our understandings beyond Chen et al.’s paper.

I do not recommend the manuscript for the publication in AMT because it has extensive problems.

Citation: https://doi.org/10.5194/amt-2022-26-RC2

Interactive discussion

Status: closed

RC1:
'Comment on amt-2022-26', Anonymous Referee #1, 25 Feb 2022
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.

General comments:

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:

In Sect. 2.1, the telescope temperature correction is mentioned without providing references. I propose citing the following articles which describe the correction scheme and its impact on the Aeolus data quality:

Weiler, F., Rennie, M., Kanitz, T., Isaksen, L., Checa, E., Kloe, J. D., Okunde, N., and Reitebuch, O.: Correction of wind bias for the lidar on-board Aeolus using telescope temperatures, Atmos. Meas. Tech. 14, 7167–7185, https://doi.org/10.5194/amt-14-7167-2021, 2021.

Rennie, M. P., Isaksen, L., Weiler, F., Kloe, J., Kanitz, T., and Reitebuch, O.: The impact of Aeolus wind retrievals in ECMWF global weather forecasts, Q. J. R. Meteorol. Soc., https://doi.org/10.1002/qj.4142, 2021.

The authors should clarify what is meant by “It should give only a small quality improvement for Aeolus wind products” (p.5, l. 12) – the change in the update rate of the AUX_TEL or the implementation of the telescope temperature correction? Both measures have improved the global average wind bias, while the latter one had a much higher impact.

The information on the deployed radiosondes provided in Sect. 2.2 is too sparse to evaluate the validation capabilities of the acquired wind data used for the comparisons. In particular, the authors should add details on the vertical resolution and accuracy.

The authors often use the term “similar” when discussing the results of the wind comparisons, particularly in Sect. 3.3. These qualitative statements should be substantiated with numbers. In this context, Fig. 8 is also only of qualitative nature and does not allow conclusions to be drawn. I suggest to plot the wind speed differences versus latitude instead.

Page 15, l. 16: The mean difference of the Rayleigh-clear winds compared to the radiosondes should read “0.19±0.71 (0.13±1.01) m/s” in accordance with Fig. S7.

I strongly suggest to add a summarizing table which provides an overview of the statistical results from the comparisons of the different datasets, periods, ascending/descending orbits.

In Sect. 4, the authors compare their results with previous studies which reported much higher systematic errors of the Rayleigh-clear and Mie-cloudy winds. However, an explanation for these discrepancies is not given. The authors should consider that previous studies were based on preliminary Aeolus data, whereas they validated re-processed data from baseline 10 which, most importantly, includes the telescope temperature correction which strongly reduces the wind biases. This should be clarified.
Citation: https://doi.org/10.5194/amt-2022-26-RC1
RC2: 'Comment on amt-2022-26', Anonymous Referee #2, 28 Feb 2022

“Intercomparison of wind observations from ESA’s satellite mission Aeolus, ERA5 reanalysis and radiosonde over China”, by Boming Liu, Jianping Guo, Wei Gong, Yong Zhang, Lijuan Shi, Yingying Ma, Jian Li, Xiaoran Guo, Ad Stoffelen, Gerrit de Leeuw, and Xiaofeng Xu, Atmos. Meas.Tech. Discuss., https://doi.org/10.5194/amt-2022-26-RC1, 2022

This manuscript describes a validation study that is relevant to Atmospheric Measurement Techniques in the topic of Aeolus L2B wind product over China. The authors describe a statistical intercomparison analysis between the Aeolus L2B wind product and wind data provided by radiosondes and ERA5 model over China.

General comment

The authors used two different periods to compare wind data obtained from the Aeolus L2B wind product with those by radiosondes and ERA5: from 20 April to30 September for radiosondes and from 9 July to 30 September for ERA5 model. The manuscript is not well-structured. The dataset is not suited for discussions of the statistical comparison. The manuscript has not been revised sufficiently in the methodology for the statistical comparison after the submission to ACP. Compared to the manuscript submitted to ACP, the manuscript states opposite results regarding to comparison between Aeolus L2B wind product (Rayleigh-clear) and wind observed by radiosondes or the wind speed differences for radiosonde and ERA5 zonal winds. There are explanation sentences for Figures S1 through S7. However, the figures and reference paper are not shown in the manuscript. The manuscript significantly lacks of the scientific quality and reliability.

Chen et al. have already published a very similar paper using ERA5 and radiosondes over China based on different months (July to December 2019 and May to October 2020). Compared to this manuscript, their manuscript is clearly structured, and all used methodologies are well explained. The manuscript does not extend our understandings beyond Chen et al.’s paper.

I do not recommend the manuscript for the publication in AMT because it has extensive problems.

Citation: https://doi.org/10.5194/amt-2022-26-RC2

Boming Liu, Jianping Guo, Wei Gong, Yong Zhang, Lijuan Shi, Yingying Ma, Jian Li, Xiaoran Guo, Ad Stoffelen, Gerrit de Leeuw, and Xiaofeng Xu

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https://doi.org/10.5194/amt-2022-26-supplement

Boming Liu, Jianping Guo, Wei Gong, Yong Zhang, Lijuan Shi, Yingying Ma, Jian Li, Xiaoran Guo, Ad Stoffelen, Gerrit de Leeuw, and Xiaofeng Xu

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Short summary

Aeolus is the first satellite mission to directly observe wind profile information on a global scale. However, Aeolus wind products over China were thus far not evaluated by in-situ comparison. This work is the comparison of wind speed on a large scale between the Aeolus, ERA5 and RS , shedding important light on the data application of Aeolus wind products.


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