the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 19 Feb 2026
A High-Resolution Tropopause Folding Dataset over China from 2014–2023
Abstract. Tropopause folds are a primary mechanism for stratosphere-to-troposphere transport (STT), significantly influencing tropospheric ozone, air quality, and regional weather. However, a multi-year, high-resolution folding dataset for China has been lacking. To address this gap, we developed a comprehensive tropopause folding dataset for China and its surrounding regions using the ERA5 reanalysis data and a three-dimensional labeling method for the period 2014–2023. This dataset is distinguished by its decade-long coverage (2014–2023) and an unprecedented combination of high spatial (0.25°×0.25°) and temporal (hourly) resolutions across 37 vertical levels, which collectively facilitate a detailed analysis of the spatiotemporal characteristics of folds in these regions. We validated the dataset's accuracy and its capability to capture the full evolution of folding events by comparing it with global datasets and multiple case studies of stratospheric intrusions. The high-resolution dataset not only aligns with large-scale climatology from previous studies but also resolves finer details that were previously smoothed out. Furthermore, this dataset reveals the distinct spatiotemporal distribution of tropopause folds over China. Folding events over China were found to occur predominantly in winter and spring, with significantly lower frequencies in summer and autumn. Spatially, shallow folds are concentrated along the subtropical jet stream, while medium folds peak over the Tibetan Plateau and Sichuan Basin in winter. Deep folds, though less frequent, have a notable impact on southwestern China, including the Tibetan Plateau, where they can substantially affect surface ozone levels. This dataset provides a solid foundation for in-depth investigations of STT mechanisms and the subsequent impacts of tropopause folds on near-surface atmospheric composition and extreme weather events, thereby serving as a valuable resource for the atmospheric science community.
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Status: open (until 31 Mar 2026)
- RC1: 'Comment on essd-2025-664', Anonymous Referee #1, 23 Feb 2026 reply
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RC2: 'Comment on essd-2025-664', Anonymous Referee #2, 26 Feb 2026
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The manuscript developed a high-resolution tropopause folding dataset over China from 2014–2023, which has important applications in research on near-surface atmospheric composition, climate change, and extreme weather events. The manuscript is well-written. Specific comments are as follows:
- L15-16: As shown by the author’s analysis, shallower intrusions account for a larger proportion. So, besides near-surface atmospheric composition and extreme weather events, I think this tropopause folding dataset might be more important for climate research on stratosphere-to-troposphere exchange (STE).
- L18-24: STE in the vicinity of the tropopause fold occurs in regions of turbulence and diabatic processes. Specifically, stratospheric air near the tropopause fold, characterized by high ozone, low water vapor, and high potential vorticity (PV), descends into the troposphere; meanwhile, tropospheric air with abundant water vapor, carbon monoxide, aerosols, and low PV is also transported into the stratosphere.
- L29: What do you mean by “downward advection”? Convection?
- L69-70: The phrase “the folding data provided by this dataset … alongside 37 vertical pressure levels” sounds strange. How can tropopause folding be divided into 37 levels? This is not clear in this study, please rephrase it.
- L91-93: Please describe in detail how you assign the five labels.
- Sect. 3.2.2: Validation with a case study is always challenging. There are some puzzling features in this study: As seen in Figs. 7 and 8, fewer deep intrusions occurred on the rear (west) side of the cut-off low, while more occurred ahead of the low. Typically, there are strong downdrafts on the west side of a cut-off low and updrafts on the east side, so it can be seen in Fig. 7a that the medium intrusions primarily occurred on the rear side of the low. Meng et al. (2024 and 2026) analyzed this 2019 event in detail, focusing on how stratospheric ozone is transported to the near-surface and its temporal evolution. Their results show that stratospheric ozone mainly intrudes from the west side of the NECV, with almost no intrusions from the east side. The results regarding deep intrusions in this study seem to reach the opposite conclusion and are at odds with the known dynamics of cut‑off lows. Could the cyclonic PV near the tropopause fold in the upper troposphere ahead of cut-off low have been misidentified as stratospheric signals in your calculation? So, I have some doubts about whether this datasets is suitable for detailed regional case studies. (Meng, K., Zhao, T., Bai, Y., Wu, M., Cao, L., Hou, X., Luo, Y., and Jiang, Y.: Tracing the origins of stratospheric ozone intrusions: direct vs. indirect pathways and their impacts on Central and Eastern China in spring–summer 2019, Atmos. Chem. Phys., 24, 12623–12642, https://doi.org/10.5194/acp-24-12623-2024, 2024; Meng, K., Zhang, J., Gong, S., Bai, Y., Wu, M., Luo, Y., and Zhao, T., Exploring the three-dimensional effects of direct and indirect stratospheric intrusions on ozone pollution in Eastern China with a novel technique, Atmospheric Research, 336, 2026, 108868)
- Sect. 3.2.3: I think this is not a good case. I would suggest using an event with tropospheric air entering the stratosphere, which would be more interesting and would also avoid overlap with existing studies such as Bartusek, S., Wu, Y., Ting, M., Zheng, C., Fiore, A., Sprenger, M., and Flemming, J.: Higher-Resolution Tropopause Folding Accounts for More Stratospheric Ozone Intrusions, Geophysical Research Letters, 50, e2022GL101 690, https://doi.org/10.1029/2022GL101690, 2023.
Citation: https://doi.org/10.5194/essd-2025-664-RC2 -
RC3: 'Comment on essd-2025-664', Anonymous Referee #3, 09 Mar 2026
reply
General comments:
Tropopause folds are an important atmospheric process that influences both atmospheric chemistry and tropospheric weather. This work focused on STT over China and nearby regions, where the topography of the Tibet Plateau may influence STT development in East Asia. In this study, the authors utilised a 10-year (2014-2013) ERA5 reanalysis dataset (hourly, 0.25x0.25 degree resolution), supported by a three-dimensional labelling method, to develop a high-resolution tropopause folding dataset for China and surrounding areas. They confirmed that their newly derived distribution patterns of tropopause folds align well with previous studies. Additionally, they showed that the new dataset captured more detailed fold distribution features due to the high-resolution dataset used. The methodology is clearly described, and the dataset produced has proven to be useful for future diagnostic studies. Overall, this work introduces a novel dataset which will enhance the understanding of STT in East Asia. This manuscript is well written, and I recommend publishing it in ESSD after a minor revision.
Specific comments:
In the introduction, the authors emphasised the importance of STT, particularly regarding tropospheric ozone. They could expand this to include ozone precursors (such as Br and I) and stratospheric aerosols, based on recent studies. For example, Schill et al. (2025) reported that STT can inject them into the Arctic free troposphere, impacting tropospheric ozone chemistry. Additionally, I noticed that a widely cited review paper, although somewhat dated, on STE by Stohl et al. (2003) was not mentioned.
Schill, G. P., Froyd, K. D., Murphy, D. M., et al.: Widespread trace bromine and iodine in remote tropospheric non-sea-salt aerosols, Atmospheric Chemistry and Physics, 25, 45–66, https://doi.org/10.5194/acp-25-45-2025, 2025.
Stohl, A., Haimberger, L., Scheele, M. P., and Wernli, H.: Stratosphere–troposphere exchange: A review, and what we have learned from STACCATO, Journal of Geophysical Research: Atmospheres, 108, 8516, https://doi.org/10.1029/2002JD002490, 2003.
Technical corrections:
Line 5: “decade-long coverage”: this statement is incorrect, as 2014-2023 only covers ~10 years.
Line 27: Change “Akritidis et al., 2016; Lin et al., 2015; Akritidis et al., 2010” to Akritidis et al., 2016, 2010; Lin et al., 2015”
Line 63: Tibetan Plateau (TP) - TP should be defined early when it appear in the first time, eg in line 13, rather than here.Line 90: isofurface should be isosurface
Line 100: Physical variables like sfold, mfold, and dfold should be better expressed in italic to distinguish them from normal words.
Lines 109-111: I cannot see how “These cases demonstrate that our dataset can successfully capture the complete evolution of tropopause folds during stratospheric intrusion
events.” Maybe you should add: “As shown below in Section XYZ, we demonstrated ….” If this is the case.
Line 117: When you see “a folding belt over China”, you need to specify their locations, e.g. between latitude A and B, for readers who are not familiar with the local topography.
Lines 125-126: “The difference is the highest (∼209%) in spring and the lowest (∼114%) in summer. “ Are they relative differences? And how did you calculate them?
Line 148: remove “(TP)”
Line 174: again, either use PT or Tibet Plateau.
Line 154: Dfold should be dfold, as it is not a word.
Line 165: for y= x line, it is better to use 1:1 line.
Line 194: Dfold should be dfold in itaiic
Line 231: Tibetan Plateau (TP) and the Sichuan Basin(SCB), see my comments above.
Citation: https://doi.org/10.5194/essd-2025-664-RC3
Data sets
A High-Resolution Tropopause Folding Dataset over China from 2014-2023 Le Cao, Yujia Yang, Liqiang Xu, Mengke Wang https://doi.org/10.5281/zenodo.17446871
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Minor correction: Please consider a small language edit for consistency. In the manuscript, the terms “stratospheric intrusion” and “stratosphere-to-troposphere transport (STT)” are sometimes used interchangeably. Adding a brief clarification early in the introduction to distinguish these terms would help readers.