Spring and summer time ozone and solar ultraviolet radiation variations over Cape Point, South Africa

du Preez, David J.; Ajtić, Jelena V.; Bencherif, Hassan; Bègue, Nelson; Cadet, Jean-Maurice; Wright, Caradee Y.

doi:https://doi.org/10.5194/angeo-37-129-2019

Articles | Volume 37, issue 2

https://doi.org/10.5194/angeo-37-129-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/angeo-37-129-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 37, issue 2

Regular paper

|

06 Mar 2019

Regular paper |

| 06 Mar 2019

Spring and summer time ozone and solar ultraviolet radiation variations over Cape Point, South Africa

David J. du Preez, Jelena V. Ajtić, Hassan Bencherif, Nelson Bègue, Jean-Maurice Cadet, and Caradee Y. Wright

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Final revised paper (published on 06 Mar 2019)
Preprint (discussion started on 07 Jun 2018)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC1: 'referee comment', Anonymous Referee #1, 18 Jul 2018
- AC1: 'Response to RC1', David Jean du Preez, 17 Sep 2018
RC2: 'review of manuscript angeo-2018-56', Anonymous Referee #2, 30 Jul 2018
- AC2: 'Response to RC2', David Jean du Preez, 17 Sep 2018

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Publish subject to revisions (further review by editor and referees) (19 Sep 2018) by Petr Pisoft

AR by David Jean du Preez on behalf of the Authors (19 Sep 2018) Author's response

ED: Referee Nomination & Report Request started (01 Oct 2018) by Petr Pisoft

RR by Anonymous Referee #1 (10 Oct 2018)

RR by Anonymous Referee #3 (04 Dec 2018)

Suggestions for revision or reasons for rejection

The authors used ground-based UV-B data to derive UV index values and correlate these values with space born ozone data, along with the use of a model to investigate the contribution of low ozone air masses due to the polar vortex, over the Cape Point in South Africa.

The abstract is clear and concise, while the introduction provides an overview of former knowledge regarding the link between the ozone and solar UV radiation at ground level.
The authors may advice the below comments in order to improve their manuscript.
General Comments
The structure of the text does not help the reader to easily follow the data analysis. For example the authors mention that the UVI data are derived on an hourly basis from UV-B measurements [are these hourly or hourly averaged? And what is the original recording frequency of the UV-B measurements?]. Then at a later point the mention that these are hourly average values, while they introduce the SZA values as another parameter later on.
I find this very confusing and I recommend that the authors should provide all the necessary details in one section, so that the reader will avoid going back and forth in order to follow the steps of the analysis.
Specific Comments
2.1 UV data
I believe that this section is still poor regarding the description of the ground-based data. Details should be provided on the accuracy of the data, the change in the calibration factors, the intercomparisons between different instruments, how the homogenisation of the data was performed, how the application of the different calibration factors was performed (blockwise of there was a time interpolation between two calibrations?). The authors included table 1 but this is more like a log book. Please consider to include some graphs in this section that will visualise what you give in table 1.
2.2 Column ozone data
This section needs to be augmented. There are so many studies regarding the OMI ozone data (e.g. Huang et al. 2017, Zempila et al. 2017 and many more), that provide insight regarding the accuracy of the OMI ozone product. Thus I suggest that the authors should revise the literature and elaborate more on the accuracy of this product.
2.3. Transport model
Did you run the model only for specific, low-ozone cases as you show later on?
2.4. Method
It would be useful to have an explanatory introduction in this section, so that the reader can overview the steps of your analysis.
2.4.2 Determination of clear-sky days
Here the authors should include previous studies in order to highlight the fact that cloud-free determination is not a trivial task, especially since UV data are not always hugely impacted by thin clouds (Zempila et al., 2017).
2.4.3 Correlations
Here you introduce SZA as an additional parameter, while you don’t mention how you manipulated the UV-B data (did you take the values every 10 minutes, did you get the 10-minute averages?).
You should also mention why you decided to take 10 minute SZA intervals. A time interval of 10 minutes includes different ranges of SZAs in Spring and in Summer. Please elaborate more towards this aspect.
3.2 Correlation between the amount of ozone and UVI
Why do you think the strongest anticorrelation is seen at 25 SZA. Is it due to the accuracy of the data (which should be better towards lower SZAs), or specific atmospheric conditions? Did you check if any change is seen when you discriminate between morning and afternoon (e.g. 25 SZA morning, 25 SZA afternoon)?
4 Conclusion
You don’t mention the use of the model in this section in order to support your related comments.

Thank you.

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ED: Publish subject to revisions (further review by editor and referees) (07 Dec 2018) by Petr Pisoft

AR by David Jean du Preez on behalf of the Authors (17 Jan 2019)

ED: Referee Nomination & Report Request started (24 Jan 2019) by Petr Pisoft

RR by Anonymous Referee #3 (25 Jan 2019)

RR by Anonymous Referee #1 (18 Feb 2019)

ED: Publish as is (21 Feb 2019) by Petr Pisoft

AR by David Jean du Preez on behalf of the Authors (22 Feb 2019)

Short summary

Reduced atmospheric ozone results in increased solar ultraviolet radiation (UVR) at the surface which may potentially negative impact public health. We aimed to assess whether or not the break-up of the Antarctic ozone hole had an impact on ozone and UVR at Cape Point (South Africa). We found a moderate inverse relationship between ozone and UVR at midday on clear-sky days. The Antarctic ozone hole had a limited effect on ozone levels while tropical air masses more frequently affected the site.