Articles | Volume 25, issue 19
https://doi.org/10.5194/acp-25-12213-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.Shift in cold-point tropopause trends derived from radiosonde, satellite and reanalysis data
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- Final revised paper (published on 07 Oct 2025)
- Preprint (discussion started on 11 Feb 2025)
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Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor
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RC1: 'Comment on egusphere-2025-82', Anonymous Referee #1, 31 Mar 2025
- AC1: 'Reply on RC1', Mona Zolghadrshojaee, 15 Jul 2025
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RC2: 'Comment on egusphere-2025-82', Anonymous Referee #2, 02 Apr 2025
- AC2: 'Reply on RC2', Mona Zolghadrshojaee, 15 Jul 2025
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AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
AR by Mona Zolghadrshojaee on behalf of the Authors (15 Jul 2025)
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ED: Referee Nomination & Report Request started (16 Jul 2025) by Farahnaz Khosrawi
ED: Publish subject to minor revisions (review by editor) (23 Jul 2025) by Farahnaz Khosrawi

AR by Mona Zolghadrshojaee on behalf of the Authors (24 Jul 2025)
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ED: Publish as is (25 Jul 2025) by Farahnaz Khosrawi

AR by Mona Zolghadrshojaee on behalf of the Authors (31 Jul 2025)
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The authors employed radiosonde, GNSS-RO, and reanalyses to update the long-term variations of temperature in the tropical upper troposphere and lower stratosphere, with a particular focus on cold point temperature. As the authors mention in the introduction, there are already many previous studies that use various data sources, including reanalysis, radiosonde, and GNSS-RO. However, a detailed comparison with previous studies is necessary to highlight the novelty of the present study. Furthermore, while the authors attempted to conduct their research using multiple datasets with high vertical resolution, they did not reveal novel or more refined features, nor did they propose new mechanisms for existing trends. Despite the study's objective to quantify trends in both space and time, it does not address the scientific questions that exist in this area. The current state of the manuscript lacks sufficient novelty for publication in the Atmospheric Chemistry and Physics.
Major Comments
1 As suggested by Highwood and Hoskins (1998), the cold-point is only a reliable tropopause definition when the lower stratosphere is not close to being isothermal, i.e., within the deep tropics. Beyond the deep tropics, the validity of the physical significance of cold point identified in the research region [30S-30N] must be assured.
2 What are the differences between the trend term derived from multivariate linear regression and that derived from conventional linear regression? Furthermore, it is crucial to ascertain the magnitude of the contributions of the additional terms (QBO, ENSO, SAOD) in the multivariate linear regression.
3 GNSS-RO measurements exhibit pronounced irregularities in the tropics compared to middle latitudes. The authors use a relatively large grid (30° longitude × 10° latitude) to ensure sufficient data sampling. However, early single GNSS-RO missions were capable of providing only about 100 profiles per day globally. For instance, the CHAMP (2001-2007) and GRACE (2006-2007) satellites each provided approximately 130 daily profiles. By contrast, the COSMIC constellation, operational since late 2007, provides about 2,500 measurements daily. This substantial disparity highlights significant sampling inhomogeneity. Given the use of multiple missions to construct long-term observations, how do the authors account for sampling biases arising from mission prioritization?
4 What implications might be drawn from the observation of significant upper troposphere warming in conjunction with insignificant temperature trends in both the cold point and lower stratosphere, as illustrated in Figure 6? Furthermore, it is important to consider the implications of these phenomena in relation to radiative or radiative-dynamical balances.
5 A discussion is also required regarding the discrepancy between the trends derived from different datasets.
6 An important question concerns the apparent shift in long-term trends around the year 2000. While the authors have proposed several potential mechanisms for this shift, a more thorough discussion is needed to fully explore these possibilities.
7 Given the apparent decoupling of upwelling trends and warming trends, it is necessary to explore alternative mechanisms that could explain the observed changes. The authors propose a correlation between the warming of the cold point and the weakening of BDC (Ln 305). This relationship should be quantitatively assessed through a rigorous analysis of reanalysis data.
Regarding the zonal-mean dynamical variables from Martineau et al. (2018) (covering 1958-2016), clarification is needed as to whether the vertical residual velocities were: (1) calculated following Martineau's methodology, or (2) obtained directly from the archived data. The relevant description in Lines 184-186 should be revised to clarify this point, or alternatively, the Data Availability statement should be updated accordingly.
Minor comments
Section 2.1 requires rewording. The methodology suggests that the cold point is determined for each radiosonde profile prior to the gridding procedure.
Ln 152-154 Please rephrase this sentence
Ln 158 balloon reading?
Ln 175 It is necessary to establish the reasons for the observation of a comparatively wider range of cold points in reanalyses as compared with radiosonde observations.
Ln 194 In fact, the short-term variations are left in the error term
It appears that reference to Table 1 has not been made in Ln 326-332.