Ozone Trend Analysis in Natal (5.4°S, 35.4°W, Brazil) Using Multi-Linear Regression and Empirical Decomposition Methods over 22 Years of Observations

Round 1

Reviewer 1 Report

I have carefully reviewed the technical note entitled "Ozone trend analysis in Natal (5.4°S, 35.4°W) using multi-linear regression and empirical decomposition methods over 22 years of observations" and am impressed with the quality of the work. The authors have conducted a thorough and well-executed study, contributing valuable insights to the field of ozone trend analysis for the long-term period of 22 years. The methodology section is robust, and the authors' choice of multi-linear regression (MLR) and empirical decomposition methods (such as EAWD) is justified. In addition, the authors compared the time series with satellite products which show good agreement among them. The authors apply these methods to study the variability and trend of ozone in Natal in three forms: (1) the Total Columns of Ozone (TCO), (2) the tropospheric partial column of ozone (Trop-CO) and (3) the stratospheric partial column of ozone (Strat-CO). In the conclusions, the authors highlight the identification of five distinct modes linked to semi-annual, annual, QBO1, QBO2, and solar forcings within the Natal TCO dataset. This analysis proves crucial in comprehending the long-term behavior of ozone. The use of a 22-year dataset adds significance to the study, allowing for a comprehensive analysis of ozone trends in the tropics.

Overall, I believe that this technical note is very well-written and makes a significant contribution to the scientific literature on ozone trends. I recommend that the manuscript be accepted for publication in its present form in the Remote Sensing journal.

Author Response

The reviewer made no comments and recommended the manuscript be accepted for publication as it is. The authors would like to thank him/her for the time he/she took to complete the review and for his/her positive feedback.

Author Response File: Author Response.pdf

Reviewer 2 Report

Title:

Ozone trend analysis in Natal (5.4°S, 35.4°W) using multi-linear regression and empirical decomposition methods over 22 years of observations.

General Comments:

The manuscript is well written, and provides a compared analysis on the variability and trends of ozone in Natal (5.4°S, 35.4°W) using a new decomposition method named Empirical Adaptive Wavelet  Decomposition (EAWD) and traditional multi-linear regression (MLR), EMD methods. The emphasis on comparing analysis was particularly noteworthy, as it enables to make evidence-based decisions. Several comments can be found as follows.

Additional Comments/Questions:

1、              Three methods, namely the multi-linear regression (MLR), EMD and EAWD were compared in this research. It was suggested list the compared indicators on the results in one table.

2、              As the Ozone was highly spatially varied, Ozone from the RS data and observed data may not be comprable.

3、              Figure 2 ,4  are not clear enough.

Author Response

We thank the reviewer for her/his appreciation and comments. Our study aims to demonstrate the effectiveness of the EAWD method in analyzing ozone variability and trends separately in the troposphere and the stratosphere. As suggested by the reviewer, table 1 has been improved and provides an overview of the detected modes, their percentage contribution, the associated forcing, and trend estimates. In addition, figures 2 and 4 have been enlarged to improve their clarity.

The changes are highlighted in blue in the revised manuscript.

Concerning ozone variability, as pointed out by the reviewer, tropospheric and stratospheric ozone abundances can vary on short-term scales due to various processes, particularly photochemistry and transport. However, our study focused on analyzing the annual variability and trends. To achieve this, we used monthly averaged data time series, filtering out any small-scale variability observed in RS and satellite observations.

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors applied a new trend analysis method for total ozone. A trend analysis was performed by eliminating natural variations in ozone. The new method better represents ozone fluctuations than the traditional method of MLR. I have a few questions.

1) Is the magnitude of the trend large enough relative to the uncertainty in the observation?

2) It is difficult to visually identify trends in the time series of TCO or Strat-CO (Fig. 5a and 5c). Thus, I wonder if it is necessary to check whether there is a trend in natural forcings. Only then it can be said that the trend change is of artificial origin.

3) There is no mention of how forcing is defined in advance in MLR.

Author Response

The authors thank the reviewer for his/her appreciation and relevant suggestions. That helped improve our paper and make it more focused and clearer. We hope we have responded appropriately and met the reviewer’s and editor’s expectations.

A more detailed response is given in the enclosed file and the revised manuscript.

Author Response File: Author Response.pdf

Reviewer 4 Report

Title:

- The title is clear and indicative of the study's focus, though it could be enhanced for specificity. Including the geographical location (Natal, Brazil) would provide immediate context for the reader.

Abstract:

- Content Overview: The abstract effectively outlines the background, objectives, methods, and key findings of the study. However, it lacks a concise statement of the research problem and its broader significance.

- Methodological Detail: There is a brief mention of the methods used, but the abstract would benefit from a succinct explanation of the Empirical Adaptive Wavelet Decomposition (EAWD) method, especially how it compares to and differs from the Empirical Modal Decomposition (EMD) and Multi-Linear Regression (MLR).

- Findings and Implications: The results are summarized, but the abstract could be improved by explicitly stating the main implications and contributions of the research, thus providing a clearer picture of the study's importance.

Keywords:

- The chosen keywords are relevant but could be refined to better reflect the core themes of the study. Incorporating specific terms from the title and abstract, such as "EAWD," would improve consistency and searchability.

Introduction:

- Literature Review: The introduction provides a comprehensive review of existing literature on ozone variability and trends, establishing a solid background. However, it could be more focused on defining the specific niche the study aims to fill.

- Research Aims: The introduction should clearly articulate the research question and objectives. It currently offers a general overview but lacks a direct statement of the study's specific aims and hypotheses.

- Structure Overview: Including a brief outline of the paper's structure would guide the reader through the study's flow and content.

Materials and Methods:

- Clarity and Detail: This section is thorough and detailed, offering a clear description of the data sources, processing, and analysis methods. However, given the technical nature of the content, simplifying complex descriptions could make the section more accessible.

- Quality Control and Validation: There's a need for more explicit information on the quality control measures and validation processes applied to the ground-based and satellite ozone data.

- Methodological Rationale: A brief explanation of the rationale and assumptions behind the chosen methods, particularly in separating tropospheric and stratospheric ozone, would provide more insight into the study's approach.

Results:

- Presentation and Analysis: The results are logically presented and discussed. However, adding descriptive statistics or summary tables would offer a clearer, more immediate understanding of the data.

- Visual Representations: Graphical displays of the ozone time series and their variability modes would enhance the reader's comprehension of the trends and patterns observed.

- Uncertainty and Statistical Significance: More detailed information on the statistical tests used and measures of uncertainty for the trend estimates would strengthen the credibility and reliability of the findings.

Conclusions:

- Summarization of Findings: The conclusions effectively summarize the main findings. Still, they could be expanded to more explicitly discuss the broader implications of these findings for ozone research and policy.

- Recommendations and Applications: The study would benefit from offering specific recommendations or potential applications arising from its findings.

- Acknowledgment of Limitations: A discussion of the study's limitations and the challenges encountered would provide a more balanced view of the research.

Overall Assessment:

- The article is comprehensive and contributes valuable insights into ozone trend analysis. However, improvements in explicitly communicating the research problem, simplifying technical language, and enhancing the discussion of implications and applications would increase its impact and accessibility. Additionally, a more focused and guided introduction, along with a more detailed methodological justification, would enhance the overall coherence and effectiveness of the paper.

Generally good a few MINOR preposition errors (with, on, etc) and suffix inconsistencies (e.g. stratosphere or stratospheric )

Author Response

There must be a technical problem. Comments from Reviewer#3 and Reviewer#4 are the same.

The authors thank the reviewer for his/her appreciation and relevant suggestions. That helped improve our paper and make it more focused and clearer. We hope we have responded appropriately and met the reviewer’s and editor’s expectations.

A more detailed response is given in the enclosed file.

Author Response File: Author Response.pdf