Study on the influence of ENSO on total columns of ozone over the Tibetan Plateau

Wang, Haoyue; Xiao, Feihong; Yu, Ke; Bian, Jianchun; Li, Dan; Liu, Qianyu

doi:10.5194/egusphere-2026-2146

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https://doi.org/10.5194/egusphere-2026-2146

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04 May 2026

| 04 May 2026

Study on the influence of ENSO on total columns of ozone over the Tibetan Plateau

Haoyue Wang, Feihong Xiao, Ke Yu, Jianchun Bian, Dan Li, and Qianyu Liu

Abstract. The El Niño-Southern Oscillation (ENSO) and the distinctive topographic features of the Tibetan Plateau (TP) exert a significant influence on the stratosphere-to-troposphere transport (STT) process. Their combined effects further amplify the spatiotemporal variability of tropospheric ozone (O₃) concentrations. To investigate the impact of ENSO on total column ozone (TCO) over the TP and the underlying mechanisms, this study employs the Weather Research and Forecasting Model with Chemistry (WRF-Chem). Results demonstrate that the single-synthesis simulation using WRF-Chem outperforms the multi-year simulation of the Whole Atmosphere Community Climate Model (WACCM) in capturing tropospheric TCO, zonal wind, potential height, and temperature. Over the TP, except in autumn, the variations in TCO within the lower stratosphere and troposphere exhibit opposite phases during El Niño and La Niña years. Specifically, TCO in the lower stratosphere is primarily regulated by the Brewer-Dobson circulation (BDC) and potential height. In contrast, TCO in the troposphere is shaped not only by potential height but also by STT processes and regional vertical circulation. The thermal effect of the TP plays a pivotal role in modulating the subtropical jet stream (STJ), potential height, and vertical circulation—with notable phase reversals observed between El Niño and La Niña years. Furthermore, the thermal effect of the TP acts in synergy with the Hadley Circulation (HC) to drive changes in the STJ, thereby exerting a significant impact on the spatiotemporal distribution of tropospheric O₃ over the TP.

Received: 15 Apr 2026 – Discussion started: 04 May 2026

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Haoyue Wang, Feihong Xiao, Ke Yu, Jianchun Bian, Dan Li, and Qianyu Liu

Status: final response (author comments only)

RC1:
'Comment on egusphere-2026-2146', Anonymous Referee #1, 25 May 2026
Summary:
Wang et al. (2026) study on the influence of ENSO on TCO over the TP. The logic, methodology, and description of this paper should be improved in the future. First of all, the scientific questions do not follow your title and topic. Second, ozone data are from reanalysis data rather than satellite observations. Third, the analysis period is too short and limits the samples of ENSO events, which impacts the confidence of statistical results. Fourth, some formats and figures do not meet the requirements.
In summary, I think this article does not satisfy the requirements for publication in ACP and I therefore reject it. The following are detailed comments that I hope will be helpful to the authors.

Major comments：
Lines 75-80: This study focuses on the influence of ENSO on TCO over the TP. It is the paper title and key point. However, this study tries to address the STT response to ENSO and its associated impacts on tropospheric O3. As the tropospheric O3 accounts for only 10% of TCO, I am very confused why the author emphasizes tropospheric O3 rather than stratospheric O3, which accounts for 90% of TCO.

Line 90: ERA5 ozone is reanalysis data, not observations. I suggest the author should use satellite data for ozone.

Line 105: Why does the author identify El Niño and La Niña events over the period 2001-2020? I feel it is odd because the ENSO events are identified by CPC from 1950 to the present.

Line 105-110: Why does the author add the impact of ENSO on East Asia? Is there a linkage between it and TP-TCO?

Table 1: The number of samples on El Niño events is too low, which may impact your statistical results. In addition, these ENSO events do not involve some very strong events, like 1982-83, 1997-98, 2007-08, 2010-11 et al. If you wonder the potential confounding effects of IOD, I think the ENSO signal will be major when it is very strong.

Line 135: “Since the CAM-Chem boundary dataset is only available for the 2001-2020 period, this study restricts……”. I do not think it is the right reason for the short analysis period. Firstly, in addition to CAM-Chem, there are other boundary sources, like MOZART4 (Emmons et al., 2010), CAMS (Inness et al., 2019), GEOS-Chem (Lin et al., 2020), and WACCM (Marsh et al., 2013). Secondly, even though the CAM-Chem limits your study period, it does not impact the analysis of observations.

Line 150: I am confused about the method proposed by Kawase et al. (2009). Why do you use it? Please give more details.

I suggest the results of Figures 1-3 should be added to Section 3 Results. In addition, Figures 1-3 show that neither the simulations of WACCM nor WRF-Chem capture the TCO during some seasons. This does not seem to support your points.

Table 2: During the spring of the ENSO phase, the mean stratospheric tracer flux relative to the climate mean is too big, 760% and 120% higher. How do you get these results? Are they significant? Please give more details.

Minor comments：
Line 65: Why do you choose the WRF-Chem model rather than other models? Please give more reasons.

Line 70: Is there a linkage between the “Asian water tower” and the TP-TCO change? If it is, please add an introduction. If it is not, please delete it.

Line 75: “PacificSSTs”-->Pacific SSTs

Line 200: “2.4 three-dimensional……”-->2.4 Three……

Equations 1-3 are not clear. Please improve the resolution.

Where is the description or introduction of Table 2 in Section 3.1?

Figures 5-13: They have no statistical test.
Citation: https://doi.org/10.5194/egusphere-2026-2146-RC1
- AC1:
  'Reply on RC1', Fei hong Xiao, 12 Jun 2026
  We are grateful for the reviewers’ rigorous and insightful evaluation of our work. Their constructive critique has prompted substantive revisions to strengthen the scientific rigor and clarity of the manuscript. Key methodological refinements and expanded analyses are detailed in the responses below.
  This study focuses on the Tibetan Plateau (TP) to elucidate ENSO's differential modulation mechanisms on ozone distribution across vertical layers:
  
  (i) Tropospheric ozone (≈10% of total column ozone, TCO), influenced by both local photochemistry and stratosphere-troposphere exchange (STE), acts as a regional pollutant with direct radiative forcing and ecological impacts;(ii) Stratospheric ozone (≈90% of TCO) governs global radiation balance and UV protection. This dual-perspective approach addresses the complex interplay between STE-driven transport and photochemical processes under ENSO forcing.
  
  Satellite observation datasets will be systematically incorporated for model validation in subsequent research.
  
  The 2001–2020 analysis period was selected to align with the temporal coverage of WRF-Chem's chemical boundary conditions, ensuring consistency in emission inventories.
  
  ENSO modulates TP's TCO variability through Pacific-East Asian (PEA) teleconnection, which alters East Asian monsoon circulation—particularly during spring when biomass burning and regional ozone transport dominate TP's TCO anomalies.
  
  Future work will explicitly examine strong ENSO events (e.g., 1997–1998, 2015–2016) to enhance statistical robustness.
  
  In the present study, a single chemical boundary condition dataset was intentionally adopted to reduce variability associated with boundary-condition settings and to ensure a clearer attribution of ozone variability to ENSO-related signals. Incorporating multiple chemical boundary condition datasets may introduce additional uncertainties stemming from differences in underlying emission inventories, which could complicate the interpretation and intercomparison of simulation results. We agree that sensitivity analyses using alternative chemical boundary condition datasets would be valuable. However, such investigations fall beyond the scope of the current study and warrant a separate, dedicated assessment to systematically evaluate the influence of emission-inventory discrepancies on ozone simulations over the TP.
  
  The Kawase et al. (2009) composite simulation method was adopted to preserve WRF-Chem's high-resolution advantage while circumventing prohibitive computational costs for long-term ENSO studies—a well-established trade-off in regional modeling (cf. Manciu et al., 2023).
  
  Elevated TCO biases in autumn (Figs 1–3) are likely attributable to complex seasonal transition processes over TP (e.g., East Asian monsoon retreat, South Asian High weakening). These dynamics exhibit phase-dependent responses to ENSO that require targeted future investigation.
  
  Anomalies represent deviations in stratospheric tracer influx to the troposphere between ENSO-phase sensitivity experiments and climatological simulations, quantifying STE intensity variations over TP under ENSO forcing.
  
  WRF-Chem was chosen for its:
  
  (i) Superior resolution over global models;(ii) Proven reliability in ENSO-chemistry coupling studies (Evans and McCabe, 2010; Ratna et al., 2014; Xi and Sokolik, 2016; Manciu et al., 2023).
  
  The phrase "Asian water tower" will be removed per suggestion.
  
  3 & 4. All figure/table specifications and presentational details will be rigorously reviewed.
  We appreciate your constructive suggestions.
  
  We will add a description about Table 2.
  
  Significance testing for composite analysis figures is precluded by the methodological design.
  
  Citation: https://doi.org/10.5194/egusphere-2026-2146-AC1
RC2:
'Comment on egusphere-2026-2146', Anonymous Referee #2, 27 May 2026

This paper investigates the impact of ENSO on the total column ozone (TCO) over Tibetan Plateau (TP) during 2001–2020 based on WRF-Chem simulations. Their results suggest that the variations of TCO over TP within the lower stratosphere and troposphere exhibit opposite phases during El Niño and La Niña years. The thermal effect of TP is found to be the key factor for modulating the subtropical jet stream (STJ), potential height, and vertical circulation, to drive changes in the STJ and affect the spatiotemporal distribution of tropospheric ozone over TP. I think this is an interesting study on the variations of total column ozone (TCO) over TP. Nevertheless, there are several issues needed to be addressed
(1) The WRF-Chem simulation was verified using reanalysis data. It is suggested to include the validation results with observation data.
(2) The paper adopts the STT event discrimination method (3D marking method). For the high PV areas with disconnected layers in the troposphere, how does this method distinguish it from the tropopause folding event? Please give more explanations.
(3) The analysis results indicate that the springtime tropospheric ozone anomalies are affected by biomass burning and regional transport. However, quantitative evidences are needed. It is recommended to add sensitivity experiments on biomass burning to further quantify the contributions of these processes.
(4) The relationship between ENSO and temperature anomalies in BDC and TP regions is analyzed, but the mechanism behind this relationship is not clear. In addition, the Quasi-Biennial Oscillation (QBO) is also one of the important processes affecting the distribution of stratospheric ozone. It is suggested to include the analysis of its influence in the analysis.
(5) The results in autumn (especially under different ENSO phases) are relatively special. It is recommended to increase the simulation area and discuss the influence of large-scale circulation shifts (e.g., Asian monsoon retreat and weakening of the South Asian High) on this phenomenon.
(6) The supplementary evaluates the meteorological elements at various altitudes of the troposphere under different ENSO phases. It is suggested to add the assessment of stratospheric meteorological elements.

Citation: https://doi.org/10.5194/egusphere-2026-2146-RC2
- AC2:
  'Reply on RC2', Fei hong Xiao, 12 Jun 2026
  Thank you for your positive evaluation of this study and for highlighting its novelty in examining the influence of ENSO on total column ozone over the Tibetan Plateau. We appreciate your constructive comments and careful reading of the manuscript. The issues you raised are valuable for improving the clarity and robustness of our work. In the revised version, we will address these concerns in detail:
  We appreciate the suggestion regarding satellite validation. Future studies will incorporate satellite observations for systematic verification of model simulations.
  
  To address concerns about the origin of high PV areas, this study implements a spatial validation protocol beyond the 3D tagging method (threshold: vertically consecutive points with PV ≥ 2 PVU and specific humidity q < 0.1 g kg⁻¹). Specifically, we examine a ±2 grid-point perimeter around initially identified regions to detect contiguous zones with PV > 2 PVU and q < 0.1 g kg⁻¹. This refinement effectively discriminates between genuine stratosphere-troposphere exchange (STE) events and detached high-PV air masses.
  
  Sensitivity experiments on biomass burning emissions will be integrated into our future research framework.
  
  Building on the insightful critique of ENSO-ozone linkages, we will:(i) Investigate ENSO's modulation of Brewer-Dobson Circulation (BDC) and thermal anomalies over the Tibetan Plateau (TP); (ii) Prioritize analysis of quasi-biennial oscillation (QBO) impacts on stratospheric ozone transport pathways in subsequent work.
  
  We commit to in-depth examination of the complex relationships between East Asian summer monsoon retreat timing and diverse ENSO phases/types (Eastern Pacific vs. Central Pacific modes).
  
  Verification modules for key stratospheric variables (temperature, geopotential height, wind fields) will be supplemented in the revised manuscript.
  
  Citation: https://doi.org/10.5194/egusphere-2026-2146-AC2

Haoyue Wang, Feihong Xiao, Ke Yu, Jianchun Bian, Dan Li, and Qianyu Liu

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Haoyue Wang, Feihong Xiao, Ke Yu, Jianchun Bian, Dan Li, and Qianyu Liu

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Short summary

This study employed atmospheric modeling simulations to demonstrate that El Niño-Southern Oscillation events modulate spatial distribution patterns and temporal trends of ozone over the Tibetan Plateau. This modulation occurs primarily through alterations in atmospheric wind fields, circulation systems, and the region's distinctive thermal forcing mechanisms.


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