This manuscript provides a detailed and quantitative assessment of wind and trajectory errors in reanalyses using the highly valuable Strateole-2 balloon data covering the equatorial and subtropical regions. Both the methodology and explanations are reasonable and presented in sufficient detail. I have no major comments, and would only like to point out minor typos and the ordering of figures and tables.

• Throughout the manuscript, both Strateole 2 and Strateole-2 are used. It would be better to unify them into a single form.
• Although this can be resolved during the proof stage, there are instances where acronyms introduced earlier are written out in full later in the manuscript (e.g., UTLS). Please check these occurrences for consistency.
• Page 2, Line 53: “We choose to focus on winds because the errors and biases are more important than for temperature”. Although a reference is provided, this statement may still be debatable depending on perspective. From the reader’s viewpoint, it remains unclear why wind errors and biases are considered more important than those of temperature. A brief explanation would be helpful.
• Page 3, Lines 84–86: “Balloons flown at … 'STR' (stratosphere) flights.” This content is already mentioned in Lines 47–48, so you may consider deleting this sentence.
• Figure 1: Visually, the balloon trajectories from the 2021 campaign (bottom panels) appear fewer than those from the 2019 campaign (top panels). Please double-check that there is no issue.
• Page 7, Line 169: “-2.08” should be “-2.09” based on Table 1.
• Page 7, Line 172: “Concardiasi” – what does this mean? I could not find this word in Google.
• I recommend swapping the order of Figures 4 and 5, since Figure 5 is referenced earlier in the text.
• Page 8, Line 210: “panel b” should be “panel a”?
• Page 10, Lines 224–226: This paragraph seems to duplicate content mentioned earlier.
• Tables 3 and 4 are not cited in the text. I also recommend swapping their order, since zonal wind is consistently discussed earlier in the manuscript.
• Page 16, Line 315: “aersosols” should be “aerosols.”
• Page 17, Line 325 and Page 18, Line 356: “ispoycnic” should be “isopycnic.”

Review of Strateole 2 Balloons Reveals Persistent Errors in Reanalyzed Winds and Trajectory Calculations in the Tropical Lower Stratosphere

In this paper, superpressure balloon measurements from the Strateole 2 campaign have been used to investigate errors in ERA5 reanalysis winds and the dispersion of trajectories in the equatorial lower stratosphere. The analysis appears sound, and the results are useful, especially in relation to forecasting trajectories for future campaigns. The paper can be considered for publication after the authors address the following comments and suggestions:

Comments and Suggestions

1. The location of the balloon launch should be marked in Figure 1. Additionally, clarify what the different colors represent in the figure and update the figure caption accordingly.

2. Figure 2 is interesting. What is the reason for the large differences in forecasted trajectories between the two launches that occurred during the same season?

3. Line 2010: For zonal wind (panel a, not b), remove the extra parenthesis.

4. Line 180: Please discuss the importance of the Gaussian distribution of errors.

5. The authors attribute biases in wind to missing components of Kelvin wave variability in the reanalysis. What were the phases and amplitudes of the Kelvin waves during the campaign period? Is there any supporting evidence from other observations?

6. Rossby waves have comparable amplitudes to Kelvin waves over the analyzed latitudes. Why is the effect of Rossby waves on wind bias minimal compared to Kelvin waves?

7. It would also be useful to provide a figure showing the errors in the direction of forecasted/modelled trajectories, similar to Figure 8.

8. Line 275: The sentence “in other words, many poorly modelled trajectories are poor from the start because the initial wind is already wrong” reads awkwardly. Please consider rephrasing for clarity.