The Southern Hemisphere Blocking Index in the ERA5 and the NCEP/NCAR Datasets: A Comparative Climatology for the Period 1940–2022
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript entitled “The Southern Hemisphere Blocking Index in the ERA5 and the NCEP/NCAR Datasets: A Comparative Climatology for the Period 1940–2022” presents a relevant scientific contribution by offering a detailed climatology of atmospheric blocking over the Southern Hemisphere, based on two widely recognized reanalysis datasets (ERA5 and NCEP/NCAR) spanning more than eight decades. The use of a one-dimensional blocking index, applied systematically and supported by a rigorous statistical approach, represents a significant advancement in understanding the spatial and seasonal variability of these systems in the Southern Hemisphere — a region historically less studied in the literature.
The methodology is robust and well documented, including spectral reconstruction via Fourier transform and objective criteria for identifying blocking events, ensuring the reproducibility of the study. The analysis is thorough, with appropriate use of statistical tests that support the interpretations provided. The manuscript is well structured, complies with the journal’s formatting guidelines, and presents figures and references that are current and relevant.
As a suggestion for improvement, the authors are encouraged to include a brief sensitivity analysis regarding the parameters adopted in the blocking index — particularly the latitudinal limits between 35°S and 50°S — in order to reinforce the robustness of the results. A careful review of the English language is also recommended to correct minor technical inconsistencies. Additionally, the authors may consider summarizing some of the more detailed descriptions in the results section to improve the overall readability.
Recommendation: Accept with minor revisions.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe presented manuscript is devoted to the climatology of atmospheric blockages in the Southern Hemisphere using two well—known reanalyses — ERA5 and NCEP/NCAR - over a long period of observations (1940-2022). The work was carried out at a high scientific level and is of interest both to specialists in the field of meteorology and climatology, and to the wider scientific community studying the impact of large-scale atmospheric processes affect the weather and climate.
The authors applied a one-dimensional blocking index at 500 gPa to identify blocking events. They conducted a detailed analysis of seasonal, longitude, and regional features of the frequency, intensity, and duration of blockages, and compared the results between the two reanalyses. Such a comparison has not been carried out with such a degree of detail before, which makes the study relevant and a new contribution to the field of climatology in the Southern hemisphere.
Among the main conclusions are:
The maximum frequency of blockages is concentrated at the date line (170°W), which persists in all seasons.
Secondary maxima are observed in the southern Atlantic Ocean, as well as less pronounced ones in the southeastern Pacific and southwestern Indian Oceans.
The most intense blockages occur in the Pacific and Atlantic Oceans; in the Indian Ocean, they are recorded only in the ERA5 data.
The longest blockages are observed in winter in the South Pacific and Atlantic oceans.
A comparison of ERA5 and NCEP showed a high degree of consistency (differences of less than 2% in almost all longitudes), with the exception of the 50°E point.
The research methodology is well-founded, and the description of the methods is quite detailed and understandable. The authors also presented an original approach to the statistical comparison of the two reanalysis data, which is an important achievement.
Comments and suggestions:
• Keywords : I suggest removing the general word "reanalysis" from the keywords and instead specifying the specific names of the products used — ERA5 and NCEP/NCAR. This will increase the accuracy of article search in scientific databases.
• Article structure : Chapter 2 ("Materials and Methods") contains a significant number of analysis results, which might be better moved to the "Results" section. The "Conclusions" section contains an extensive analysis of the results obtained, but its name can be adjusted to simply "Conclusions", since it corresponds more to the final section than to a full-fledged discussion..
• Figure 2: Flip the image to portrait orientation to improve readability in the electronic version of the magazine.
• Choosing the blocking episode (August 18-29, 2001): Please clarify why this particular period was chosen — was it a unique case of 12 consecutive days of blocking or just a typical example?
• Number of locks found : It would be useful to add a quantitative comparison of the number of locks found in ERA5 and NCEP/NCAR over the same time period (for example, 1948-2022) in order to assess the differences in the effectiveness of the algorithm in different reanalysis.
In general, I believe that this work is a valuable contribution to the study of the climatology of blocking anticyclones in the Southern Hemisphere. It is distinguished by the rigor of its methodology, the depth of its analysis, and the clarity of its formulations. Taking into account the above remarks and their implementation, the article deserves publication in the Atmosphere journal.
Recommended for publication after making minor edits.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsI enjoyed reading the manuscript. The material is quite solid. The text organization and illustrations are good. In my perspective, the manuscript is close to becoming publishable. I've suggested several additions for the readers.
1. I didn't entirely grasp the authors' decision to use data from both reanalyses. ERA5 is much more progressive and detailed. You are evaluating the blocking results when there are 100 cells of one reanalysis and one cell of the other. I'd limit myself to ERA5.
2. How valid do you believe it is to compare blocking events in reanalysis data to radiosonde data, assuming that reanalysis incorporates this data?
3. The authors should analyze the relationship between the occurrences and the location of the blocking with the primary centers of atmospheric action, such as the South Atlantic, South Indian, and Antarctic anticyclones, as well as El Niño.
4. Has the impact of Antarctica on the geography of block formation been assessed?
5. Is it possible to predict tropical storm trajectories and their relationship to blocking in the Southern Hemisphere?
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
