the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 Sep 2024
Response of the link between ENSO and the East Asian winter monsoon to Asian anthropogenic aerosols
Abstract. We use coupled and atmosphere-only simulations from the Precipitation Driver and Response Model Intercomparison Project to investigate the impacts of Asian anthropogenic sulfate aerosols on the link between the El Niño-Southern Oscillation (ENSO) and the East Asian Winter monsoon (EAWM). In fully-coupled simulations, aerosol-induced cooling extends southeastward to the Maritime Continent and the north-western Pacific. Remotely, this broad cooling weakens the easterly trade winds over the central Pacific, which reduces the east-west equatorial Pacific sea surface temperature gradient. These changes contribute to increasing ENSO's amplitude by 17 %, mainly through strengthening the zonal wind forcing. Concurrently, the El Niño-related warm SST anomalies and the ensuing Pacific-East Asia teleconnection pattern (i.e. the ENSO-EAWM link) intensify, leading to an increased EAWM amplitude by 18 % in the coupled simulations. Therefore, in response to the increasing frequency of El Niño and La Niña years under Asian aerosol forcing, the interannual variability of the EAWM increases, with more extreme EAWM years. The opposite variations in the interannual variability of the EAWM to Asian aerosols in atmosphere-only simulations (−19 %) further reflect the importance of ENSO-related atmosphere-ocean coupled processes. A better understanding of the changes of the year-to-year variability of the EAWM in response to aerosol forcing is critical to reducing uncertainties in future projections of variability of regional extremes, such as cold surges and flooding, which can cause large social and economic impacts on densely populated East Asia.
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2024-2770', Anonymous Referee #1, 11 Feb 2025
This study documented the impact of Asian anthropogenic aerosols on the relationship between ENSO and the East Asian winter monsoon using coupled and atmosphere-only numerical model experiments. Through a comparison of two sets of model experiments: the baseline simulation with present-day (year 2000) level of aerosols and the simulation with 10-fold increase in sulfate concentrations/emissions over Asia (10°–50°N, 60°–140°E), the authors identified a 17% increase in the ENSO amplitude and a 18% increase in the EAWM amplitude in the coupled model, but a 19% decrease in the EAWM amplitude in the atmosphere-only simulation. The reasons for the aerosol impacts were provided by the authors. The contents of this work are suitable for publication after modifications. Below are specific comments for the authors to consider when they revise the manuscript.
Specific comments:
P1, L23-26: It is unclear how an improved understanding of the changes in the year-to-year EAWM variability is linked to reducing uncertainties in future projections of variability of regional extremes. There is no evidence for this claim. Suggest removing this inference.
P1, L32: Feng et al (2010) is about ENSO impacts. More relevant previous studies of EAWM impacts may be added to support this statement, for example, Zhou and Wu (2010) and Wang et al. (2022) talked about the impacts of EAWM on precipitation over East Asia and western North Pacific.
Zhou, L.-T., and R. Wu, 2010: Respective impacts of the East Asian winter monsoon and ENSO on winter rainfall in China. J. Geophys. Res., 115, D02107.
Wang, Z.-Z., R. Wu, and Y.-Q. Wang, 2022: Impacts of the East Asian winter monsoon on winter precipitation variability over East Asia-western North Pacific. Climate Dynamics, 58(11-12), 3041-3055.
P2, L9-11: In addition to subjecting to the ENSO impact, the EAWM variability may be partly independent of ENSO and affect climate over East Asia and the western North Pacific, as pointed out by previous studies (e.g., Wu et al. 2014; Chen et al. 2015; Wang et al. 2021, 2022), which pinpoints the importance of studying EAWM changes, such as the results of atmosphere-only model simulations in this study.
Wu, R., W. Chen, G. Wang, and K.-M. Hu, 2014: Relative contribution of ENSO and East Asian winter monsoon to the South China Sea SST anomalies during ENSO decaying years. J. Geophys. Res., 119(19), 5046-5064.
Chen, Z., R. Wu, and W. Chen, 2015: Effects of northern and southern components of the East Asian winter monsoon on SST changes in the western North Pacific. J. Geophys. Res., 120(9), 3888-3905.
Wang, Z.-Z., and R. Wu, 2021: Individual and combined impacts of ENSO and East Asian winter monsoon on the South China Sea cold tongue intensity. Climate Dynamics, 56(11-12), 3995-4012.
Wang, Z.-Z., R. Wu, and Y.-Q. Wang, 2022: Impacts of the East Asian winter monsoon on winter precipitation variability over East Asia-western North Pacific. Climate Dynamics, 58(11-12), 3041-3055.
P4, L10-11: What are those slow and fast responses? Please add relevant references.
P4, L15-16: A factor of 10 increase: How realistic is this 10-fold increase? Is there any evidence or previous studies for supporting this?
P4, L32: How to evaluate the performance of fSST baseline simulation as climatological SST is specified to force the model?
P6, L7-10: Disagree. According to the figures, the temperature and precipitation changes show distribution different from the anomalies in the baseline experiment. For example, the Asian land region is mostly covered by temperature decrease except for the coast. This cannot be explained using enhanced ENSO amplitude and strengthened anticyclone over the western North Pacific.
P6, L23-24 and L26-27: This indicates a shift in the mean state (stronger mean EAWM) due to the continent cooling induced by aerosol increase. How to understand the reduced EAWM variability under stronger mean EAWM? Any speculation?
P6, L30: Southeasterly? Do you mean “southeastward”?
P7, L20: “Consistently” > “Consistent”
Figure 4: Need to add notations for the colors.
P8, L15 and L19: Reduced west-east SST gradient is expected to lead to weaker advective feedback as the advection term is proportional to the mean zonal SST gradient, right?
P8, L32: remove the word “occur”
P9, L14-15: The preceding sentences talk about the mean state changes. How they lead to the ENSO amplitude increase is explained in the next paragraph. Suggest adding “as explained below” in the end of the sentence for transition.
P10, L9-10: Reduced west-east SST gradient is expected to be unfavorable for the advection effect. How could it lead to an increase in ENSO amplitude?
Citation: https://doi.org/10.5194/egusphere-2024-2770-RC1 -
AC1: 'Reply on RC1', Zixuan Jia, 03 May 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2770/egusphere-2024-2770-AC1-supplement.pdf
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AC1: 'Reply on RC1', Zixuan Jia, 03 May 2025
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RC2: 'Comment on egusphere-2024-2770', Anonymous Referee #2, 26 Feb 2025
This study leverages PDRMIP simulations to investigate the interactions between the East Asian Winter Monsoon (EAWM), ENSO, driven by the effects of Asian aerosols, offering a novel perspective on this important topic. Overall, the manuscript is well-structured and scientifically rigorous, presenting valuable insights into the impact of Asian anthropogenic aerosols on ENSO and EAWM. Below are some key areas for improvement:
Major Comments
- Clarification of Aerosol Types Considered: The manuscript focuses on the effects of sulfate aerosols over Asia, while absorbing aerosols (e.g., black carbon) are not explicitly discussed. Previous studies have shown that absorbing aerosols can have comparable influences on atmospheric circulation and precipitation, despite their lower atmospheric burden. In particular, Asian absorbing aerosols are known to significantly affect the Walker circulation, a key process examined in this study. While it is valid to focus primarily on scattering aerosol effects, this should be clearly specified in the title and abstract to avoid concerns about overlooking absorbing aerosol impacts.
- Lack of Direct Analysis of Aerosol Perturbation and Effects: While the study systematically investigates the climate responses to aerosol perturbations, it does not directly show the aerosol changes and effects themselves. Adding patterns and seasonality of aerosol optical depth (AOD) and effective radiative forcing (ERF) would provide a more intuitive representations of the aerosol perturbations, which could also help explain the spatial and seasonal climate responses.
Specific Comments:
- The analysis uses different time periods for the coupled simulations (1965–2014) and fixed-SST simulations (1994–2005). Please explain the reasoning behind this difference. Additionally, please double-check the results to ensure that the different periods do not introduce inconsistencies in the comparison.
- In PDRMIP, aerosol perturbations cover the entire Asian region (10°–50°N, 60°–140°E), but most figures cover only East Asia. This could lead to an overlook of South Asian aerosol effects. It would be helpful to demonstrate the AOD and ERF of SAsia aerosols and discuss the potential contributions.
- The results from the SUL×10Asia experiment should be added to Figures 1, 3, and 5, to better compare with the baseline simulation.
- Statistical Significance Testing: Please include statistical significance tests for the SUL×10Asia – baseline results to ensure the statistical significance of the climate responses. And for the significance test, the method by Wilks (2016, https://doi.org/10.1175/BAMS-D-15-00267.1) will be more robust than the Student’s t-test.
- Please add units in the plots for easier reading.
- The authors need to double-check the Supplementary figures:
- Figure S4 captions: "As in Figures 1a-c, but for SON”, but variables in Fig1 and S4 are different, please double check.
- P9 L9 “Aleutian Low deepens with a southward shift in the coupled baseline simulation (Figs. S4a, S2a).” While Fig.S2a shows fixed-SST SLP and 850hPa UV
Citation: https://doi.org/10.5194/egusphere-2024-2770-RC2 -
AC2: 'Reply on RC2', Zixuan Jia, 03 May 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2770/egusphere-2024-2770-AC2-supplement.pdf
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2024-2770', Anonymous Referee #1, 11 Feb 2025
This study documented the impact of Asian anthropogenic aerosols on the relationship between ENSO and the East Asian winter monsoon using coupled and atmosphere-only numerical model experiments. Through a comparison of two sets of model experiments: the baseline simulation with present-day (year 2000) level of aerosols and the simulation with 10-fold increase in sulfate concentrations/emissions over Asia (10°–50°N, 60°–140°E), the authors identified a 17% increase in the ENSO amplitude and a 18% increase in the EAWM amplitude in the coupled model, but a 19% decrease in the EAWM amplitude in the atmosphere-only simulation. The reasons for the aerosol impacts were provided by the authors. The contents of this work are suitable for publication after modifications. Below are specific comments for the authors to consider when they revise the manuscript.
Specific comments:
P1, L23-26: It is unclear how an improved understanding of the changes in the year-to-year EAWM variability is linked to reducing uncertainties in future projections of variability of regional extremes. There is no evidence for this claim. Suggest removing this inference.
P1, L32: Feng et al (2010) is about ENSO impacts. More relevant previous studies of EAWM impacts may be added to support this statement, for example, Zhou and Wu (2010) and Wang et al. (2022) talked about the impacts of EAWM on precipitation over East Asia and western North Pacific.
Zhou, L.-T., and R. Wu, 2010: Respective impacts of the East Asian winter monsoon and ENSO on winter rainfall in China. J. Geophys. Res., 115, D02107.
Wang, Z.-Z., R. Wu, and Y.-Q. Wang, 2022: Impacts of the East Asian winter monsoon on winter precipitation variability over East Asia-western North Pacific. Climate Dynamics, 58(11-12), 3041-3055.
P2, L9-11: In addition to subjecting to the ENSO impact, the EAWM variability may be partly independent of ENSO and affect climate over East Asia and the western North Pacific, as pointed out by previous studies (e.g., Wu et al. 2014; Chen et al. 2015; Wang et al. 2021, 2022), which pinpoints the importance of studying EAWM changes, such as the results of atmosphere-only model simulations in this study.
Wu, R., W. Chen, G. Wang, and K.-M. Hu, 2014: Relative contribution of ENSO and East Asian winter monsoon to the South China Sea SST anomalies during ENSO decaying years. J. Geophys. Res., 119(19), 5046-5064.
Chen, Z., R. Wu, and W. Chen, 2015: Effects of northern and southern components of the East Asian winter monsoon on SST changes in the western North Pacific. J. Geophys. Res., 120(9), 3888-3905.
Wang, Z.-Z., and R. Wu, 2021: Individual and combined impacts of ENSO and East Asian winter monsoon on the South China Sea cold tongue intensity. Climate Dynamics, 56(11-12), 3995-4012.
Wang, Z.-Z., R. Wu, and Y.-Q. Wang, 2022: Impacts of the East Asian winter monsoon on winter precipitation variability over East Asia-western North Pacific. Climate Dynamics, 58(11-12), 3041-3055.
P4, L10-11: What are those slow and fast responses? Please add relevant references.
P4, L15-16: A factor of 10 increase: How realistic is this 10-fold increase? Is there any evidence or previous studies for supporting this?
P4, L32: How to evaluate the performance of fSST baseline simulation as climatological SST is specified to force the model?
P6, L7-10: Disagree. According to the figures, the temperature and precipitation changes show distribution different from the anomalies in the baseline experiment. For example, the Asian land region is mostly covered by temperature decrease except for the coast. This cannot be explained using enhanced ENSO amplitude and strengthened anticyclone over the western North Pacific.
P6, L23-24 and L26-27: This indicates a shift in the mean state (stronger mean EAWM) due to the continent cooling induced by aerosol increase. How to understand the reduced EAWM variability under stronger mean EAWM? Any speculation?
P6, L30: Southeasterly? Do you mean “southeastward”?
P7, L20: “Consistently” > “Consistent”
Figure 4: Need to add notations for the colors.
P8, L15 and L19: Reduced west-east SST gradient is expected to lead to weaker advective feedback as the advection term is proportional to the mean zonal SST gradient, right?
P8, L32: remove the word “occur”
P9, L14-15: The preceding sentences talk about the mean state changes. How they lead to the ENSO amplitude increase is explained in the next paragraph. Suggest adding “as explained below” in the end of the sentence for transition.
P10, L9-10: Reduced west-east SST gradient is expected to be unfavorable for the advection effect. How could it lead to an increase in ENSO amplitude?
Citation: https://doi.org/10.5194/egusphere-2024-2770-RC1 -
AC1: 'Reply on RC1', Zixuan Jia, 03 May 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2770/egusphere-2024-2770-AC1-supplement.pdf
-
AC1: 'Reply on RC1', Zixuan Jia, 03 May 2025
-
RC2: 'Comment on egusphere-2024-2770', Anonymous Referee #2, 26 Feb 2025
This study leverages PDRMIP simulations to investigate the interactions between the East Asian Winter Monsoon (EAWM), ENSO, driven by the effects of Asian aerosols, offering a novel perspective on this important topic. Overall, the manuscript is well-structured and scientifically rigorous, presenting valuable insights into the impact of Asian anthropogenic aerosols on ENSO and EAWM. Below are some key areas for improvement:
Major Comments
- Clarification of Aerosol Types Considered: The manuscript focuses on the effects of sulfate aerosols over Asia, while absorbing aerosols (e.g., black carbon) are not explicitly discussed. Previous studies have shown that absorbing aerosols can have comparable influences on atmospheric circulation and precipitation, despite their lower atmospheric burden. In particular, Asian absorbing aerosols are known to significantly affect the Walker circulation, a key process examined in this study. While it is valid to focus primarily on scattering aerosol effects, this should be clearly specified in the title and abstract to avoid concerns about overlooking absorbing aerosol impacts.
- Lack of Direct Analysis of Aerosol Perturbation and Effects: While the study systematically investigates the climate responses to aerosol perturbations, it does not directly show the aerosol changes and effects themselves. Adding patterns and seasonality of aerosol optical depth (AOD) and effective radiative forcing (ERF) would provide a more intuitive representations of the aerosol perturbations, which could also help explain the spatial and seasonal climate responses.
Specific Comments:
- The analysis uses different time periods for the coupled simulations (1965–2014) and fixed-SST simulations (1994–2005). Please explain the reasoning behind this difference. Additionally, please double-check the results to ensure that the different periods do not introduce inconsistencies in the comparison.
- In PDRMIP, aerosol perturbations cover the entire Asian region (10°–50°N, 60°–140°E), but most figures cover only East Asia. This could lead to an overlook of South Asian aerosol effects. It would be helpful to demonstrate the AOD and ERF of SAsia aerosols and discuss the potential contributions.
- The results from the SUL×10Asia experiment should be added to Figures 1, 3, and 5, to better compare with the baseline simulation.
- Statistical Significance Testing: Please include statistical significance tests for the SUL×10Asia – baseline results to ensure the statistical significance of the climate responses. And for the significance test, the method by Wilks (2016, https://doi.org/10.1175/BAMS-D-15-00267.1) will be more robust than the Student’s t-test.
- Please add units in the plots for easier reading.
- The authors need to double-check the Supplementary figures:
- Figure S4 captions: "As in Figures 1a-c, but for SON”, but variables in Fig1 and S4 are different, please double check.
- P9 L9 “Aleutian Low deepens with a southward shift in the coupled baseline simulation (Figs. S4a, S2a).” While Fig.S2a shows fixed-SST SLP and 850hPa UV
Citation: https://doi.org/10.5194/egusphere-2024-2770-RC2 -
AC2: 'Reply on RC2', Zixuan Jia, 03 May 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2770/egusphere-2024-2770-AC2-supplement.pdf
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Massimo A. Bollasina
Wenjun Zhang
Ying Xiang
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(6168 KB) - Metadata XML
-
Supplement
(5510 KB) - BibTeX
- EndNote
- Final revised paper