the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 22 Dec 2022
Spatial characteristics of frazil streaks in the Terra Nova Bay Polynya from high-resolution visible satellite imagery
Abstract. Coastal polynyas around the Antarctic continent are regions of very strong ocean–atmosphere heat and moisture exchange, important for local and regional weather, sea ice production and water mass formation. Due to extreme atmospheric conditions (very strong offshore winds, low air temperature and humidity) the surface ocean layer in polynyas is highly turbulent, with mixing due to combined Langmuir, wind-induced and buoyancy-driven turbulence. One of the visible signs of complex interactions between the mixed layer dynamics and the forming sea ice are frazil streaks, elongated patches of high ice concentration separated by areas of open water. In spite of their ubiquity, observational and modelling analyses of frazil streaks have been very limited, largely due to the fact that their significance for heat flux and ice production is only just becoming apparent. In this study, the first comprehensive analysis of the spatial variability of surface frazil concentration is performed for the Terra Nova Bay Polynya (TNBP). Frazil streaks are identified in high-resolution (pixel size 10–15 m) visible satellite imagery, and their properties (surface area, width, spacing and orientation) are linked to the meteorological forcing (wind speed and air temperature). This provides a simple statistical tool for estimating the extent and ice coverage of the region of high ice production under given meteorological conditions. It is also shown that the orientation of narrow streaks tends to agree with the wind direction, suggesting the dominating role of the local wind forcing in their formation. Very wide streaks, in turn, deviate from that pattern, as they are presumably influenced by several additional factors, including local water circulation and the associated convergence zones. An analysis of peak wave lengths and directions determined from the images, compared to analogous open-water wave lengths computed with a spectral wave model, demonstrates a significant slow-down in the observed wave growth in TNBP. This suggests an important role of frazil streaks in modifying wind-wave growth and/or dissipation in polynyas.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
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Supplement
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
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Supplement
(14231 KB) - BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2022-1435', Anonymous Referee #1, 01 Feb 2023
This is comprehensive study on the spatial characteristics of frazil streaks using high resolution satellite imagery and how the observed characteristics relate to temperature and wind speed. Some interesting new results described and generally well written, only a few minor changes are needed in the text to be ready for publication.
General comments
You include some results at the end of introduction in the final paragraph, eg ‘as expected ice concentration increases with X faster at lower T…’ This is quite densely written, and I think just an overview of what you are going to do but not the relationships you find is what is needed at the point in the paper. You could move this to a summary after the discussion, as the discussion is relatively lengthy (which is fine) so a shorter summary of findings afterwards reiterating the main results to finish would help round off the paper nicely.
A bit more explanation/suggestion of what the mathematical relationships mean physically would help the paper flow and ensure the findings are clear throughout the results section and make it easier to read. And in the figure captions I think it would read easier if instead of putting ‘what is in the subplot’ (a), it was ‘(a) what is in the subplot….’
And I had a few general questions about frazil streaks, though I appreciate that you focused on spatial characteristics, but I wondering whether is it known how thick/deep the frazil streaks are and what their vertical structure is like? Do you have any idea how important this might be or how it might interact with the horizontal features? And what is the timescale for the development of the streaks, how long do they stick around?
Specific Comments
Lines 112-127: At the end of the introduction you put a summary what you do in the study and some of the results. Instead an overview of what you are about to present and what is in each section would work better here. You could add a summary after your discussion/conclusion and move some of this text there. If possible and remaining consider writing the summary without symbol abbreviations.
Fig 2: last figure has a different coloured background to the others which I don’t think is intentional. Label the subplots a,b,c
Line 125: remove extra space before ‘The dominant role…’
Line 140: Sept and Oct – was this due to clouds? Or is this a time when they are most likely to be seen? Do we know much about their seasonal cycle?
Line 273: do you mean correlated with as opposed to ‘consistent with the variability of the average wind speed’
Line 275: comment on ‘the area of the polynya is less determined…’ can you explain this statement?
Line 279: Potentially add a sentence clarifying that wind speed is suggested to be a dominant influence on extent and frazil concentration. You say it already, but wouldn’t harm to state it clearly after the details.
Line 294: Change ‘also indicates an area’ to ‘is in an area’
Line 311: I don’t think that wind speed is given in either figure listed, I don’t understand the comment. Sorry if I have missed something
Line 312: Do you mean ‘residuals’ instead of ‘residues’
Line 319: ‘the positive correlation between wind speed and the overall extent of the polynya’ do you mean that increased wind speeds increases the polynya extent which decreases the frazil concentration (frazil is more spread out)? Could you explain a little here
Line 325: delete ‘It seems that taking into account’
Line 327: Do you think that incorporating more observations will increase the percentage of variance explained? And can you comment on what might cause the rest, and the role of the oceanic/mixed layer conditions and potential timescales involved?
Line 331: delete extra space after ‘160 m’
Line 353: I think you mean ‘extend’ instead of ‘extent’
Line 359: is 50 m the limit of the previous study? If so, state that
Line 412: ‘forcing’, maybe phrase this as atmospheric conditions or some variations on atmospheric/sea ice/OML conditions
Line 415: redefine OML as ocean mixed layer here
Line 425: I’m not sure what you mean by ‘high dynamics’
Line 428: Remove the long bracket and split into a sentence so it reads more smoothly. Could put the relevant features in a sentence afterwards with something like ‘The features that demonstrate are’ or similar
Line 443: Change ‘stronger’ to ‘more strongly’, it isn’t currently wrong but I think it will flow better
Line 458: Redefine Cz(X), and any other symbols you used in the discussion
Line 478: delete ‘As said’
Line 482: redefine the angles you are comparing
Line 497: Remove bracket around sentence
Line 517: Remove bracket from around sentence.
Citation: https://doi.org/10.5194/egusphere-2022-1435-RC1 -
AC1: 'Reply on RC1', Katarzyna Bradtke, 20 Feb 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-1435/egusphere-2022-1435-AC1-supplement.pdf
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AC1: 'Reply on RC1', Katarzyna Bradtke, 20 Feb 2023
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RC2: 'Comment on egusphere-2022-1435', Anonymous Referee #2, 10 Feb 2023
The paper contains a very thorough analysis of frazil ice streaks in a large polynya using the possibilities of remote sensing. It is a good source of statistical information for further investigation. I particularly like the inclusion of wave modelling, which allows for understanding the significance of the findings better. I recommend publication with minor revisions.
There are a lot of symbols used in the text, a table with the variable definitions would be helpful. The paper also ends quite abruptly, one or two concluding sentences could be nice.
Specific comments:
Line 9: "as well as" humidity instead of "and"
Line 26: use commas when using "or" for synonyms: Coastal, or latent heat, polynyas etc.
Line 30: perhaps an estimate of what percentage of the heat and moisture fluxes in the ice cover of this region happen over the polynya
Line 35: please split this sentence in two to make it easier to read
Line 112 onward: the introduction has changed into a summary, please put this at the end of the paper
Line 145: the correlation with meteorological data on particular timescales is a result in itself, so this sentence belongs in the results section
Line 225: do you mean "For three events"? These specific events have not been introduced before I believe
Line 312: “with average”
Line 328: “is shown”
Line 331: “changes”
Citation: https://doi.org/10.5194/egusphere-2022-1435-RC2 -
AC2: 'Reply on RC2', Katarzyna Bradtke, 20 Feb 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-1435/egusphere-2022-1435-AC2-supplement.pdf
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AC2: 'Reply on RC2', Katarzyna Bradtke, 20 Feb 2023
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2022-1435', Anonymous Referee #1, 01 Feb 2023
This is comprehensive study on the spatial characteristics of frazil streaks using high resolution satellite imagery and how the observed characteristics relate to temperature and wind speed. Some interesting new results described and generally well written, only a few minor changes are needed in the text to be ready for publication.
General comments
You include some results at the end of introduction in the final paragraph, eg ‘as expected ice concentration increases with X faster at lower T…’ This is quite densely written, and I think just an overview of what you are going to do but not the relationships you find is what is needed at the point in the paper. You could move this to a summary after the discussion, as the discussion is relatively lengthy (which is fine) so a shorter summary of findings afterwards reiterating the main results to finish would help round off the paper nicely.
A bit more explanation/suggestion of what the mathematical relationships mean physically would help the paper flow and ensure the findings are clear throughout the results section and make it easier to read. And in the figure captions I think it would read easier if instead of putting ‘what is in the subplot’ (a), it was ‘(a) what is in the subplot….’
And I had a few general questions about frazil streaks, though I appreciate that you focused on spatial characteristics, but I wondering whether is it known how thick/deep the frazil streaks are and what their vertical structure is like? Do you have any idea how important this might be or how it might interact with the horizontal features? And what is the timescale for the development of the streaks, how long do they stick around?
Specific Comments
Lines 112-127: At the end of the introduction you put a summary what you do in the study and some of the results. Instead an overview of what you are about to present and what is in each section would work better here. You could add a summary after your discussion/conclusion and move some of this text there. If possible and remaining consider writing the summary without symbol abbreviations.
Fig 2: last figure has a different coloured background to the others which I don’t think is intentional. Label the subplots a,b,c
Line 125: remove extra space before ‘The dominant role…’
Line 140: Sept and Oct – was this due to clouds? Or is this a time when they are most likely to be seen? Do we know much about their seasonal cycle?
Line 273: do you mean correlated with as opposed to ‘consistent with the variability of the average wind speed’
Line 275: comment on ‘the area of the polynya is less determined…’ can you explain this statement?
Line 279: Potentially add a sentence clarifying that wind speed is suggested to be a dominant influence on extent and frazil concentration. You say it already, but wouldn’t harm to state it clearly after the details.
Line 294: Change ‘also indicates an area’ to ‘is in an area’
Line 311: I don’t think that wind speed is given in either figure listed, I don’t understand the comment. Sorry if I have missed something
Line 312: Do you mean ‘residuals’ instead of ‘residues’
Line 319: ‘the positive correlation between wind speed and the overall extent of the polynya’ do you mean that increased wind speeds increases the polynya extent which decreases the frazil concentration (frazil is more spread out)? Could you explain a little here
Line 325: delete ‘It seems that taking into account’
Line 327: Do you think that incorporating more observations will increase the percentage of variance explained? And can you comment on what might cause the rest, and the role of the oceanic/mixed layer conditions and potential timescales involved?
Line 331: delete extra space after ‘160 m’
Line 353: I think you mean ‘extend’ instead of ‘extent’
Line 359: is 50 m the limit of the previous study? If so, state that
Line 412: ‘forcing’, maybe phrase this as atmospheric conditions or some variations on atmospheric/sea ice/OML conditions
Line 415: redefine OML as ocean mixed layer here
Line 425: I’m not sure what you mean by ‘high dynamics’
Line 428: Remove the long bracket and split into a sentence so it reads more smoothly. Could put the relevant features in a sentence afterwards with something like ‘The features that demonstrate are’ or similar
Line 443: Change ‘stronger’ to ‘more strongly’, it isn’t currently wrong but I think it will flow better
Line 458: Redefine Cz(X), and any other symbols you used in the discussion
Line 478: delete ‘As said’
Line 482: redefine the angles you are comparing
Line 497: Remove bracket around sentence
Line 517: Remove bracket from around sentence.
Citation: https://doi.org/10.5194/egusphere-2022-1435-RC1 -
AC1: 'Reply on RC1', Katarzyna Bradtke, 20 Feb 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-1435/egusphere-2022-1435-AC1-supplement.pdf
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AC1: 'Reply on RC1', Katarzyna Bradtke, 20 Feb 2023
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RC2: 'Comment on egusphere-2022-1435', Anonymous Referee #2, 10 Feb 2023
The paper contains a very thorough analysis of frazil ice streaks in a large polynya using the possibilities of remote sensing. It is a good source of statistical information for further investigation. I particularly like the inclusion of wave modelling, which allows for understanding the significance of the findings better. I recommend publication with minor revisions.
There are a lot of symbols used in the text, a table with the variable definitions would be helpful. The paper also ends quite abruptly, one or two concluding sentences could be nice.
Specific comments:
Line 9: "as well as" humidity instead of "and"
Line 26: use commas when using "or" for synonyms: Coastal, or latent heat, polynyas etc.
Line 30: perhaps an estimate of what percentage of the heat and moisture fluxes in the ice cover of this region happen over the polynya
Line 35: please split this sentence in two to make it easier to read
Line 112 onward: the introduction has changed into a summary, please put this at the end of the paper
Line 145: the correlation with meteorological data on particular timescales is a result in itself, so this sentence belongs in the results section
Line 225: do you mean "For three events"? These specific events have not been introduced before I believe
Line 312: “with average”
Line 328: “is shown”
Line 331: “changes”
Citation: https://doi.org/10.5194/egusphere-2022-1435-RC2 -
AC2: 'Reply on RC2', Katarzyna Bradtke, 20 Feb 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-1435/egusphere-2022-1435-AC2-supplement.pdf
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AC2: 'Reply on RC2', Katarzyna Bradtke, 20 Feb 2023
Peer review completion
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Katarzyna Bradtke
Agnieszka Herman
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(2830 KB) - Metadata XML
-
Supplement
(14231 KB) - BibTeX
- EndNote
- Final revised paper