Satellite observations of aerosols and clouds over southern China from 2006 to 2015: analysis of changes and possible interaction mechanisms

Benas, Nikos; Meirink, Jan Fokke; Karlsson, Karl-Göran; Stengel, Martin; Stammes, Piet

doi:https://doi.org/10.5194/acp-20-457-2020

Articles | Volume 20, issue 1

https://doi.org/10.5194/acp-20-457-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-20-457-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 20, issue 1

Research article

|

14 Jan 2020

Research article |

| 14 Jan 2020

Satellite observations of aerosols and clouds over southern China from 2006 to 2015: analysis of changes and possible interaction mechanisms

Nikos Benas, Jan Fokke Meirink, Karl-Göran Karlsson, Martin Stengel, and Piet Stammes

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Final revised paper (published on 14 Jan 2020)
Supplement to the final revised paper
Preprint (discussion started on 04 Oct 2018)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC1: 'Satellite observations of aerosol and clouds over southern China from 2006 and 2015', Anonymous Referee #1, 30 Oct 2018
- AC1: 'First Reply to Anonymous Referee #1', Nikos Benas, 27 Nov 2018
  - RC3: 'reviews', Anonymous Referee #1, 28 Nov 2018
RC2: 'Referee Report', Anonymous Referee #2, 06 Nov 2018
- AC2: 'First Reply to Anonymous Referee #2', Nikos Benas, 27 Nov 2018
  - RC4: 'Further explanation of recommendation to reject this submission', Anonymous Referee #2, 12 Dec 2018
    - AC3: 'Second Reply to Anonymous Referee #2', Nikos Benas, 16 Jan 2019
EC1: 'Authors’ responses to Referee #2’s comments should be posted first', Toshihiko Takemura, 18 Dec 2018

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Nikos Benas on behalf of the Authors (15 Feb 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (25 Feb 2019) by Toshihiko Takemura

RR by Stefan Kinne (21 Mar 2019)

RR by Anonymous Referee #3 (07 May 2019)

Suggestions for revision or reasons for rejection

This study aimed to analyze satellite observations to understand the changes and possible interaction mechanisms between aerosols and clouds over southern China. The topic is critical. However, the method and the analyses should be improved to enhance the quality of this manuscript. I suggest major changes.

Their study highlighted biomass burning as the major source to cause the changes in cloud, while the contribution of other sources was not discussed. Past studies have reported, during the study period (2006-2015), the reduction in emissions was observed not only for biomass burning but also for other sources. Because the emissions in southern China were very complicated, the contribution of other emission sources should be considered. Also, in Figure 3, the emissions of biomass burning in J-S showed an increase but the AOD decreased; From Oct to Nov, the emissions decreased but the AOD increased. These results do not seem to support their findings.

Second, natural climate conditions should be considered in the analyses. Their findings claimed the changes in cloud were mainly due to aerosols. But natural climate variability must be a critical factor to affect cloud. Without considering natural climate variability, their results may not fully reflect the situation.

Third, climate change was definitely a critical factor to influence annual variability of aerosol distribution and concentration. However, climate change was not assessed systemically in their analyses.

The robustness of the results should be investigated. I suggest to conduct statistically significance tests for the trend of cloud (spatial distribution). This would help readers to better understand the results.

I agree with the point mentioned in line 3-5 in page 3. Considering local emissions alone may cause significant problems. So, considering long-range transport is necessary.
“It should be noted that, due to the long-range transport of aerosols, local aerosol emissions are not expected to fully explain corresponding properties and characteristics of aerosol types and loads in the atmosphere of the same region.”

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ED: Reconsider after major revisions (07 May 2019) by Toshihiko Takemura

AR by Nikos Benas on behalf of the Authors (18 Jun 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (22 Jun 2019) by Toshihiko Takemura

RR by Anonymous Referee #3 (07 Jul 2019)

Suggestions for revision or reasons for rejection

My comments have not been well addressed. In addition, it is not easy to follow the changes in the manuscript. My recommendation of major changes is still remained.

“Their study highlighted biomass burning as the major source to cause the changes in cloud, while the contribution of other sources was not discussed. Past studies have reported, during the study period (2006-2015), the reduction in emissions was observed not only for biomass burning but also for other sources. Because the emissions in southern China were very complicated, the contribution of other emission sources should be considered. Also, in Figure 3, the emissions of biomass burning in J-S showed an increase but the AOD decreased; From Oct to Nov, the emissions decreased but the AOD increased. These results do not seem to support their findings.”

Reply: This comment is not well addressed. The abstract still highlights “Analyses of emissions and precipitation changes suggest that a decrease in biomass burning aerosols and an increase in precipitation played important roles in the overall aerosol reduction. But I don’t think it is correct as the relationship between the changes in biomass burning aerosols and precipitation are not clear.

“Second, natural climate conditions should be considered in the analyses. Their findings claimed the changes in cloud were mainly due to aerosols. But natural climate variability must be a critical factor to affect cloud. Without considering natural climate variability, their results may not fully reflect the situation.”

Reply: Again, natural climate variability is critical for such long-term analysis. The authors add an analysis of precipitation as they claim precipitation can affect aerosol and cloud conditions through natural variability. However, aerosols themselves have impact on precipitation through cloud. Analyzing precipitation alone does not definitely help understand the effect of natural variability.

“Third, climate change was definitely a critical factor to influence annual variability of aerosol distribution and concentration. However, climate change was not assessed systemically in their analyses.”

Reply: similar to the responses in the previous two comments, this comment has not yet been addressed. Surface temperature alone may not fully reflect the effect of climate change, which can affect dynamics for example. More effort should be put on addressing this concern.

“The robustness of the results should be investigated. I suggest to conduct statistically significance tests for the trend of cloud (spatial distribution). This would help readers to better understand the results.”

Reply: the explanation about the statistically significance test results is not clear that make readers hard to understand.

“I agree with the point mentioned in line 3-5 in page 3. Considering local emissions alone may cause significant problems. So, considering long-range transport is necessary.
“It should be noted that, due to the long-range transport of aerosols, local aerosol emissions are not expected to fully explain corresponding properties and characteristics of aerosol types and loads in the atmosphere of the same region.””

Reply: I don’t agree with this response. The studied region has significant local emission sources and long-range transport, while biomass burning emissions are just one of the emission sources. This study uses the method of satellite observations of aerosols. So, it is necessary considering other sources and long-range transport.

One new comment. Figure S4 does not sound to be correct. First of all, the emissions of all the species except NH3 are constant throughout a year. References should be provided to support this. Also, averaging each month in the period of 2006-2014 is misleading as the monthly variations in far past and recent years may be different.

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ED: Reconsider after major revisions (07 Jul 2019) by Toshihiko Takemura

AR by Nikos Benas on behalf of the Authors (16 Aug 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (22 Aug 2019) by Toshihiko Takemura

RR by Anonymous Referee #3 (16 Sep 2019)

Suggestions for revision or reasons for rejection

1) Regarding the relationship mentioned in the response, the explanation is not clear. Their explanation is purely based on a hypothesis without any evidence. A more in-depth analysis is needed.

2) The CEDS emission data is replaced by CAMS emission data, and the authors claimed the agreement is better after the replacement. However, it also raises an important concern that the results are dependent on their data selection. The authors mentioned the CEDS data is a recent, well-documented and widely used emission data set. But now they used another one. If so, how could we explain the disagreement using CEDS data? At the end of their explanation, they mentioned the CAMS emission data may not fully capture the most recent trend. The explanation confused readers. It is better to provide a further explanation. On the other hand, the authors should quantify and discuss how the uncertainty of the emission data affects the results.

3) Literature has found the obvious regional climate change in southern China during the studied period. For example, Zhang et al. (2019) found the important changes in temperature and precipitation from 2001-2010 and 2010-2015 from their table 1. The authors are suggested to provide a better review of the regional climate change in Southern China, and explain why their results have an opposite trend of those reported by other studies.

4) The HYSPLIT simulations are very rough. Using only Oct 2007 and Oct 2015 to represent the study period is questionable. Literature has shown the importance of long-range transport in southern China (i.e. Gao et al., 2012). It seems the results of this study do not agree with literature. It is better to investigate and discuss the discrepancies.

References:
Gao, X., Xue, L., Wang, X., Wang, T., Yuan, C., Gao, R., Zhou, Y., Nie, W., Zhang, Q. and Wang, W.: Aerosol ionic components at Mt. Heng in central southern China: Abundances, size distribution, and impacts of long-range transport, Science of The Total Environment, 433, 498–506, doi:10.1016/j.scitotenv.2012.06.095, 2012.

Zhang, Q., Yao, Y., Wang, Y., Wang, S., Wang, J., Yang, J., Wang, J., Li, Y., Shang, J. and Li, W.: Characteristics of drought in Southern China under climatic warming, the risk, and countermeasures for prevention and control, Theor Appl Climatol, 136(3), 1157–1173, doi:10.1007/s00704-018-2541-2, 2019.

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ED: Reconsider after major revisions (16 Sep 2019) by Toshihiko Takemura

AR by Svenja Lange on behalf of the Authors (28 Nov 2019) Author's response Manuscript

ED: Publish as is (29 Nov 2019) by Toshihiko Takemura

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Short summary

In this study we analyse aerosol and cloud changes over southern China from 2006 to 2015 and investigate their possible interaction mechanisms. Results show decreasing aerosol loads and increasing liquid cloud cover in late autumn. Further analysis based on various satellite data sets shows consistency with the aerosol semi-direct effect, whereby less absorbing aerosols in the cloud layer would lead to an overall decrease in the evaporation of cloud droplets, thus increasing cloud amount.