Review of “Multi-instrumental analysis of ozone vertical profile and total column in South America: comparison between subtropical and equatorial latitudes”

Gabriela Dornelles Bittencourt et al.

Summary and General Comments:

This paper examines long time series of vertical profile and total column data to describe the differences in behavior of ozone between a subtropical station (Santa Maria) and tropical station (Natal) in Brazil. The authors leverage the SABER instrument (vertical profile; both stations) and TOMS and OMI (total column; both stations), ozonesonde profiles (Natal), Dobson (Natal), and Brewer (Santa Maria) data. The authors validate the SABER profile data with Natal to justify its use to demonstrate the vertical profile differences between the two stations, compare TOMS and OMI to the ground-based total ozone instruments, and perform a wavelet analysis to show the effect of climate and solar oscillations on the total column and lower stratospheric ozone data.

The analyses and conclusions drawn from them are generally sound. However, the text needs a major reworking. The authors should carefully go through the paper and clean up the writing for better clarity. There are also several sections, particularly in the Introduction, that are highly repetitive. There are many times where very similar explanations of the Brewer-Dobson Circulation are invoked, for example.

A note on data availability: It is not made clear if all of the data are publicly available and where the data sets are located. I am particularly interested in locating the Santa Maria ground-based total column ozone data. Please indicate in a Data Availability section where all of the data used in this paper are located, and if they are not currently publicly available, they should be made so.

Recommendation:

While I do not find many problems with the analysis and technical details of the manuscript, the text requires substantial edits. A second version of this paper may become acceptable for publication.

Specific and Line-by-Line Comments:

Please add the SHADOZ v6 ozonesonde data doi where appropriate (e.g., Line 137) and in the reference list: https://doi.org/10.57721/SHADOZ-V06

Line 71: Natal actually has ozonesonde data dating back to 1979 on WOUDC (before SHADOZ).

Line 85: You are referring specifically to the total column ozone measurements here, correct? Please clarify.

Lines 121-125: These two sentences are not necessary and are another example of the repetitive nature of the text.

Line 139: Based on Figure 2, it looks like data only up through 2018, not 2020, have been used.

Line 139: What do you mean by “604 vertical levels?” Were the ozonesonde profiles averaged into altitude bins? If so, why 604?

Lines 142-143: “Atmosphere Survey using Broadband Emission Radiometry” for the SABER acronym is incorrect, but it was correctly defined earlier in the paper, so this can be deleted.

Line 163: Please use commas for “6,715” and “3,681” instead of “6.715” and “3.681”

Line 183: The Aura satellite, not ERS-2.

Section 2.2: I think this section can be removed. No need to spend time explaining these widely-used statistical measures. I recommend to keep Section 2.2.1, however. If the decision is made to keep this Section, the Equations 1, 2, and 3 should have “SATELLITE” not “SATELITE”

Figure 2: Similar to how Figures 3 and 4 were constructed, it would be very illuminating to see a third panel on Figure 2 showing the full time series of differences in ozone mixing ratio for coincident measurements from the two instruments (ozonesondes and SABER).

Lines 216 and 256: Better to use “coincident” than “concomitant.” As previously stated, the paper would benefit greatly from a thorough editing of the text.

Line 248: Data gaps should not really affect the comparisons of coincident satellite and ozonesonde data.

Figures 3, 4, 5, 7, and 9: What do the error bars represent? One standard deviation?

Line 319: 45N and 45-60S are mid-latitudes, not polar latitudes.

Figure 8: There are some typos in the titles of these figure panels.

Figure 8 c and d: The Natal TCO time series do not appear to be daily observations. Please check.

Table 1: What are the units of the 0.34, -0.07, -0.41, and -0.66 values? It looks like percent, but please make that clear.

Line 420: I’m not familiar with the “influence cone” for this wavelet analysis. Please provide a brief explanation as part of Section 2.2.1. I will say that Figures 10 and 11 are a nice demonstration of QBO and solar cycle oscillations on ozone amounts over the two stations.

The following is a reviewer’s report for “Multi-instrumental analysis of ozone vertical profile and total column in South America: comparison between subtropical and equatorial latitudes”

Gabriela Dornelles Bittencourt et al.

1. The introduction needs to be rewritten/restructured. The current form completely diluted the focus of this paper. The authors should rather consider a discussion of irregular distribution of global ozonesonde stations (Tarasick et al., 2019), how the Santa Maria ozonesonde can fill the observational gap in South America, and then emphasis that these data are an important addition to understand tropospheric ozone & air quality in a region where scientists are less studied before.
2. 163, does it mean that SM has a nearly doubled sampling frequency than NT? The SHADOZ network typically has once per week or fewer sampling frequency, if SM has a greater data coverage, the authors should explicitly state that SM dataset is expected to have a greater statistical power for analysis (e.g. Jaffe & Ray, 2007).
3. Figure 3: it is not very informative for ozone variability, I would like to see all individual profiles at SM plotted in thin gray from the background at each corresponding month (e.g. Fig 2 of Jaffe et al., 2018). Same for Fig 4 & 5.
4. Unlike tropospheric ozone, TCO and stratospheric ozone tend to be steadier and latitude-dependent, does this study suggest that the current SHADOZ network is sufficient to monitor tropical stratosphere, or additional stations, such as SM, are also desirable?
5. Data availability section is a requirement for AMT.
6. I found it is unpleasant to read and grammar edits/checks are required throughout the paper. There are too many to identify in the minor comments below.

l.205 “root”

l.207 delete ‘also called residuals’, e.g. MAE is also a type of residuals

l.221 ‘Variabilities the ozone’ is not English

L.389 ‘interannual’

Jaffe, D. A., Cooper, O. R., Fiore, A. M., Henderson, B. H., Tonnesen, G. S., Russell, A. G., ... & Moore, T. (2018). Scientific assessment of background ozone over the US: Implications for air quality management. Elem Sci Anth, 6, 56.

Jaffe, D., & Ray, J. (2007). Increase in surface ozone at rural sites in the western US. Atmospheric Environment, 41(26), 5452-5463.

Tarasick, D., Galbally, I. E., Cooper, O. R., Schultz, M. G., Ancellet, G., Leblanc, T., ... & Neu, J. L. (2019). Tropospheric Ozone Assessment Report: Tropospheric ozone from 1877 to 2016, observed levels, trends and uncertainties. Elem Sci Anth, 7, 39.