Aerosol Optical Properties and Types over Southern Africa and Reunion Island Determined from Ground-Based and Satellite Observations over a 13-Year Period (2008–2021)
, Nelson Bègue 1, Hassan Bencherif 1,2, Tristan Millet 1, Venkataraman Sivakumar 2,3, Valentin Duflot 1, Alexandre Baron 1,4,5, Nkanyiso Mbatha 6, Stuart Piketh 7, Paola Formenti 8 and Philippe Goloub 9
Round 1
Reviewer 1 Report (Previous Reviewer 1)
The authors have addressed most of my comments in the current version. I recommend this manuscript be accepted after clarifying and correcting the comments below.
Line 34-35: Need to introduce the acronyms before using them.
Line 168: Change ‘provides’ to ‘provide’
Line 280: In the RMSE or MBE equations, there is no 100. Could you provide the reasoning for that?
Figure 2 caption: change ‘To each color is associated an aerosol type’ to ‘Each color is associated with an aerosol type’
Line 337 to 341: I would suggest moving this paragraph to the figure 5 caption.
Line 376: I don’t think this can be the purpose of a study. The linear relationship is what you see from the data. I suggest changing this sentence to ‘The relationship between Sunphotometer and MODIS observation is investigated.’
Line 377: Change ‘correlation plot’ to ‘scatter plot’. Same for the figure 6 caption.
Line 479/486: Do you mean ‘Figure 8b’?
Line 550: Do you mean ‘Figure 9 c1-c3’?
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report (New Reviewer)
Study of Aerosol Optical Properties and Types over Southern Africa and Reunion Island Determined from Ground-Based and Satellite Observations over a 13-Year Period (2008–2021), this topic is important for understanding of the rainfall, air pollution, particles and changes of climate.
Author should add more results in the abstract, very short abstract.
It is a very important and novel topic and fits in the specific gap in the southern africa region.
Authors very well compared with other published material.
Authors groundwater based and satellites very efficiently applied and used to study aerosol optical properties and types. So many climate changes on the Island, this study may be useful to understanding what problems create in the area. how to change the climate.
I have accepted the article for publication with minor revision.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report (New Reviewer)
The manuscript "Aerosol Optical Properties and types over Southern Africa...", by Ranaivombola et al. analize aerosol properties over southern africa by means of AERONET and MODIS products and CALIPSO profiles. The dataset comprise 13 years and the results are relevant from a part of the world that haven't been characterized often. The work is centered in biomass-burning aerosols, but these are poorly characterized by AOD and AE. Better results would be obtained by taking SSA and FMF into consideration. The manuscript present some typos and definition problems that have been highlighted in the attached document. My recommendation is publish after minor review.
Comments for author File: Comments.pdf
Author Response
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This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
This manuscript examined 13 years of aerosol optical properties (i.e., aerosol optical depth and Angstrom exponent) and aerosol types over the Southern Africa region using AERONET, MODIS, and CALIOP data. The source origin of the aerosol reaching the study areas is investigated by running the HYSPLIT model. While the paper is well-organized, some places are not fully supported by the analysis as presented. I would like a revision to clarify the below questions before the paper can be published.
General comments:
1. The introduction needs a substantial revision. (1) The scientific contribution of this study is not clearly stated. The benefit this paper can bring to the community is missing in the current version. (2) Some recent work discussing the AOD spatial-temporal variation in a similar region and the same type of aerosol is not even mentioned in the introduction. For example, the recent NASA ORACLES campaign deployed in the Southeast Atlantic region specifically measures biomass burning aerosol optical properties and chemical compositions. Several papers are out there discussing the optical properties of biomass-burning aerosol in a similar regime, e.g., Redemann et al., 2021; Doherty et al., 2021; Chang et al., 2021;
2. It’s a bit difficult to understand figure 2. It seems there is no difference or very minimal difference for both AE and AOD between the four seasons, at least not clear from the current figure 2. I suggest adding some statistics for AE and AOD under different seasons.
3. Using AERONET AE to calculate the 500 nm AOD from MODIS seems problematic. Why not directly calculate the AERONET 550 nm AOD and compare it with MODIS 550 nm AOD? Also, after you convert the wavelength for AOD, I suggest calling AERONET AOD as AODAERONET, similar to AODMODIS, since AOD500 can cause confusion.
4. The authors studied AOD, AE, and aerosol types over Southern Africa with a focus on biomass-burning aerosols. As a suggestion for future study, I would love to see the analysis of aerosol single-scattering albedo as well, which infers the mixing and aging process of these BB aerosols.
Specific comments:
Line 68: Why is Terra used but not both Terra and Aqua?
Line 99: Need to mention the wavelength for AERONET AOD uncertainty.
Line 166: Two 532 channels? Do you mean the perpendicular and parallel splits of the laser beam?
Line 244: Regarding figure 3, it’s hard for me to see the primary information of this figure. The benefit of having a time series is that readers can see the trend of aerosol loading in the past years. However, this trend is not apparent in figure 3 for most stations. Meanwhile, you calculated the r, m, and b for the linear fitting, which is usually done for a scatter plot. I would suggest changing this time series to scatter plots and adding the RMSE as one parameter to indicate the goodness of fitting. If yearly variation and seasonal variation are needed, then try to color-code the scatter plots with different years or seasons.
Line 245: Is a correlation coefficient between 0.5 and 0.7 considered significant agreement?
Line 257-259: MODIS standard product only retrieves the clear sky AOD at 10 km resolution, and the level 3 product used in this study is aggregated into 1o X 1o. Do you mean the 1o X 1o grid may contain cloudy pixels, which may bias the AOD retrieval? One thing that might affect your AERONET-MODIS AOD comparison is the sub-grid variability of aerosol, which may cause a discrepancy between the AERONET and MODIS comparison. Since the AERONET only measures one specific location within a big 1o X 1o box.
Line 259-261: Following the above comment, the sub-pixel clouds may affect the MODIS retrieval but are not the main reason influencing your comparison using the level 3 MODIS product. Spatial heterogeneity of aerosol within 1o X 1o box and the un-restricted collocation are more predominant.
Line 276: Figure 5 legend, for the whisker box plot, the median is represented by the line in the box, not the box itself, correct?
Line 290: The larger difference observed here might be due to the use of the daily product for AERONET and MODIS. I would expect more consistency between the two if AERONET instantaneous AOD and MODIS level 2 products are used under a restricted spatial-temporal collocation.
References:
Doherty, S.J., Saide, P.E., Zuidema, P., Shinozuka, Y., Ferrada, G., Gordon, H., Mallet, M., Meyer, K., Painemal, D., Howell, S.G. and Freitag, S., 2021. Modeled and observed properties related to the direct aerosol radiative effect of biomass burning aerosol over the Southeast Atlantic. Atmospheric chemistry and physics: ACP., pp.1-88.
Chang, I., Gao, L., Burton, S.P., Chen, H., Diamond, M.S., Ferrare, R.A., Flynn, C.J., Kacenelenbogen, M., LeBlanc, S.E., Meyer, K.G. and Pistone, K., 2021. Spatiotemporal heterogeneity of aerosol and cloud properties over the southeast Atlantic: An observational analysis. Geophysical Research Letters, 48(7), p.e2020GL091469.
Redemann, J., Wood, R., Zuidema, P., Doherty, S.J., Luna, B., LeBlanc, S.E., Diamond, M.S., Shinozuka, Y., Chang, I.Y., Ueyama, R. and Pfister, L., 2021. An overview of the ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) project: aerosol–cloud–radiation interactions in the southeast Atlantic basin. Atmospheric chemistry and physics, 21(3), pp.1507-1563.
Reviewer 2 Report
Comments for author File: Comments.pdf
