The impact of model resolution on the Southern Hemisphere in CCSM4 idealized climate simulations

Daher, Houraa; Kirtman, Ben P.

doi:https://doi.org/10.5194/egusphere-2023-340

Preprints

https://doi.org/10.5194/egusphere-2023-340

Preprints

07 Mar 2023

| 07 Mar 2023

The impact of model resolution on the Southern Hemisphere in CCSM4 idealized climate simulations

Houraa Daher and Ben P. Kirtman

Abstract. Ocean model resolution plays a large role in accurately simulating the Southern Hemisphere circulation in both the ocean and atmosphere. Resolving the ocean mesoscale field is important as it has been shown to have a significant impact on the large-scale climate in eddy rich regions (i.e., western boundary currents, the Antarctic Circumpolar Current) which also are regions of large CO₂ absorption. The presence of ocean mesoscale features can affect sea surface temperatures, the strength and location of the storm tracks, and many other air-sea processes. Additionally, with an improvement in resolution, the eddy kinetic energy in the ocean can be expected to change considerably. The significance model resolution has on the Southern Hemisphere is examined using Community Climate System Model, version 4 ocean eddy-parameterizing and eddy-resolving simulations. The CO₂ concentrations and ozone levels are specified independently to better understand how the mesoscale field responds to extreme changes in the external forcing and the resulting climate impacts. Overall, in the eddy-parameterizing simulations, the ozone forcing is found to be more important than the changes in CO₂ concentrations for the zonal mean atmospheric temperature, zonal mean zonal wind, sea surface temperature, sea surface height, eddy kinetic energy, zonal mean ocean temperature, convective precipitation, and surface temperature. In the case of the eddy-resolving simulations, however, the CO₂ concentrations are found to be more dominant, especially in eddy-rich regions.

Received: 26 Feb 2023 – Discussion started: 07 Mar 2023

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Houraa Daher and Ben P. Kirtman

Status: closed

CEC1:
'Comment on egusphere-2023-340', Juan Antonio Añel, 06 Apr 2023

Dear authors,
Unfortunately, after checking your manuscript, it has come to our attention that it does not comply with our "Code and Data Policy".

https://www.geoscientific-model-development.net/policies/code_and_data_policy.html
The repositories that you mention in your "Code and data availability" section are not suitable for scientific publication. You must store your code and data in one of the suitable repositories listed in our policy. The repositories for code and data must be permanent, without the possibility of being deleted by the authors, accessible without limitations, and should have been available at the submission of your work. In fact, that your manuscript has been accepted for Discussions is an irregular situation and should not have happened.
Therefore, we will have to reject your manuscript unless you publish the code (CCSM4 model and modules and scripts that you use) in one of the appropriate repositories and reply to this comment with the relevant information (links and DOIs). Please, do it as soon as possible.
Also, please, remember that if you solve this with the necessary information in reply to this comment, you must include in any potentially reviewed version of your manuscript the modified 'Code and Data Availability' section with the information about the new repositories.
Juan A. Añel
Geosci. Model Dev. Executive Editor

Citation: https://doi.org/10.5194/egusphere-2023-340-CEC1
- AC1:
  'Reply on CEC1', Houraa Daher, 10 Apr 2023
  
  Dear Dr. Añel,
  The data and code used in this study has been uploaded to Zenodo and is openly available, complying with the GMD Code and Data Policy. Here is the DOI and link to the data and code.
  
  DOI: 10.5281/zenodo.7812531
  
  LINK: https://doi.org/10.5281/zenodo.7812531
  
  We will update the Code and Data Availability section in the manuscript in the potentially reviewed version we receive. Thank you.
  
  Best,
  
  Houraa Daher
  
  Citation: https://doi.org/10.5194/egusphere-2023-340-AC1
  - CEC2: 'Reply on AC1', Juan Antonio Añel, 13 Apr 2023
    
    Dear authors,
    Unfortunately, your reply does not fulfil our requirements. You have uploaded into the new repository files with output data and the scripts to analyze the data. However, we continue missing a repository for the code of the exact version of CCSM4 (and all their components (POP2, CAM-Chem, etc.)) that you use in your work.
    Therefore, your submission continues to violate our policy, and we will have to reject your manuscript unless you upload to a new repository the code requested. Please, reply to this comment with the details for the new repository.
    Juan A. Añel
    Geosci. Model Dev. Executive Editor
    
    Citation: https://doi.org/10.5194/egusphere-2023-340-CEC2
    
    AC2: 'Reply on CEC2', Houraa Daher, 17 Apr 2023
    
    Dear Dr. Añel,
    The CCSM4 code and ozone files have been uploaded to Zenodo as well and is available. The DOI and link to the code is below.
    DOI: 10.5281/zenodo.7838611
    Link: https://doi.org/10.5281/zenodo.7838611
    We will update the Code and Data Availability section accordingly. Thank you.
    
    Best,
    Houraa Daher
    
    Citation: https://doi.org/10.5194/egusphere-2023-340-AC2
RC1:
'Comment on egusphere-2023-340', Anonymous Referee #1, 10 May 2023
Review of “The impact of model resolution on the Southern Hemisphere in CCSM4 idealized climate simulations” by Houraa Daher and Ben P. Kirtman
General comments:
In this paper, the authors are examining the role of ocean model resolution on the Southern Hemisphere climate. They used the Community Climate System Model version 4 (CCSM4) to perform a suite of experiments by changing the ocean and atmospheric resolutions as well as CO₂ and O₃ forcing. This paper does not give any insights on the model development, and hence does not suit the journal Geoscientific Model Development. I have some reservations on their methods which I listed in detail below. Also, the analyses presented in the paper, in its present form, are too shallow to be published in a decent scientific journal. The authors may consider my detailed comments for revising the paper and submitting it to a more appropriate journal.
Specific comments:
The authors claim they investigate effect of ocean model resolution on the southern hemisphere climate simulated by a coupled model. However, they change the resolution of the atmospheric component as well. This is confusing. If the objective is to understand the role of ocean model resolution, then the resolution of the atmospheric model should be kept the same while changing the resolution of the ocean model. In a coupled model, the largest source of bias is the problems in simulating the effects of clouds. It depends on the atmospheric model resolution. There are plenty of works published on the cloud biases over the southern hemisphere oceans in CMIP5 coupled model experiments. These biases are more over the upwelling regions of the western boundaries due to the presence of a vast shallow cloud deck. I think that the upwelling also plays a role in these biases. When you change the ocean and atmosphere resolution simultaneously, it affects the simulations of ocean upwelling and atmospheric convection. This makes it difficult to attribute the changes in the simulated climate to the resolution of any particular model component. I see that there is a caveat in the text on the change in the atmospheric reolution. I would have accepted it if the focus of the paper was not on the impact of ocean model resolution.

Another issue is the duration of the experiments. The low-resolution simulations are performed for a longer period (100 years) while the high-resolution simulations are run for shorter durations (20 to 70 years). I suggest that all the experiments to be run for the same duration.

I had a hard time understanding the calculation of “net change”. In the equations (L130), did you divide LRC_co2 with HRC_co2? Does “/” mean “OR” in those equations?

Figures 2 – 9: I find it really difficult to read the labels due to small font sizes. More importantly, these analyses seem to be disconnected from each othere. Authors should present a coherent anaysis of the results. Also, I do not understand how these results help model developers.
Citation: https://doi.org/10.5194/egusphere-2023-340-RC1
- AC3:
  'Reply on RC1', Houraa Daher, 22 May 2023
  We appreciate the time and effort that the reviewer has dedicated to providing valuable feedback on our manuscript. We are grateful to the reviewer for their insightful comments on our study. We address their comments below and hope our response answers their concerns.
  We chose to submit to the model evaluation section of GMD because we are looking at how changes in the model resolution leads to different results in CCSM4 specifically rather than how this study can improve future model development.
  We agree that the changes the atmospheric resolution is not ideal but since previous existing experiments were set up like this we decided not to change it going forward. In response to this review we looked at another simulation that has constant year 2000 CO2 and O3 forcing and was run with 1 degree ocean and 0.5 degree atmospheric resolution and compared this to our control experiment, LRC08 (1 degree ocean and 1 degree atmosphere) to determine the impact the change in atmospheric resolution has. We quickly looked at the zonal mean zonal wind, zonal mean zonal temperature, and sea surface temperature. With an increase in atmospheric resolution and keeping the ocean resolution at 1 degree, we find that there are warmer temperatures found near the equation and cooler temperatures in the lower stratosphere but not much of a difference elsewhere. For the zonal mean zonal wind, there are faster winds at the equator through all levels in the atmosphere. And for the sea surface temperatures, there is cooling observed around Antarctica. We do not have any additional experiments with this resolution and historical CO2 or 1955 O3 forcing to compare to our other experiments in this study, however. Because we find that the change in atmospheric resolution is indeed contributing some change to the variables looked at, we will fix the paper so it doesn’t solely focus on ocean resolution but also attributes the changes observed to both the ocean and atmospheric resolution since computationally we cannot rerun the experiments to have constant atmospheric resolution.
  
  The reviewer brings up the issue of the duration of the experiments as the low resolution experiments are all 100 years and the high resolution experiments are between 20-70 years. The differences in data periods is due to what data was available for each experiment with HRC20 being the newest. We did subset our output in shorter time intervals and didn’t find any significant differences.
  
  The “/“ in the equations is signifying or not division. We will fix this in the manuscript so it is clearer and not confusing. There will be an equation for LRC and HRC for each of the forcing changes.
  
  We will improve the font size on the figures so they are easier to read. Additionally we will improve our results section so the figures shown are connected to each other.
  
  Thank you again for your comments.
  
  Citation: https://doi.org/10.5194/egusphere-2023-340-AC3
RC2:
'Comment on egusphere-2023-340', Anonymous Referee #2, 13 May 2023

Review: “The impact of model resolution on the Southern Hemisphere in CCSM4 idealized climate simulations” by Daher and Kirtman.

This manuscript investigates the impact of eddy-resolving versus eddy-parameterizing simulation in the Southern Hemisphere. Especially, the authors look at the climate response sensitivity to different CO2 concentration and ozone levels forcing using the CCSM4 community model to perform the experiments. They look at the differences induced in zonal mean atmospheric temperature, zonal mean zonal wind, sea surface temperature, sea surface height, eddy kinetic energy, zonal mean ocean temperature, convective precipitation and surface temperature. They found significant differences between low and high resolutions simulations induced by better modeling the mesoscale eddies. Moreover, they found that overall in eddy-resolving simulations the changes in CO2 concentration are more dominant, especially in eddy-rich regions, whereas in eddy-parameterization the changes in ozone levels are more dominant.
General comments and main concerns:
Overall, the paper is well written and easy to follow. For the scope of GMD I believe a more detailed description of the model used needs to be done and how novel this model comparison performance is in regard to literature or what is usually done in climate models. There are some caveats in the methodology which are for the most part addressed by the authors, like the changes in atmospheric resolution. However, this can cause significant differences in the results, I would suggest to run the simulations on the same atmospheric resolution to be very clear on the actual impact of the ocean resolution only which is the goal of this paper. Moreover, some changes in methodology like de data periods differences between simulations are not addressed and thus can be confusing when looking at the results presented. Overall, the results section is very descriptive and just show differences but don’t really explain any of them. A deeper or more thorough analysis of the results and changes observed would be needed. Indeed, it is expected that a change in resolution would produce different results but we need to know why and why the results would be better, at least here in term of physical processes representation as the simulations are very idealized. I believe the paper in present form would need more work to be suitable for publication.
Some specific comments:
Around line 80: The model description that has been used needs to be much more detailed than what it is right now, some key parametrizations used, land model, ice model, coupler…
Around line 95: When describing the different experiments, it could be clearer to define the control experiment first and then the idealized simulations and thus what the comparison to the control experiments would mean.
Line 92 and 104: As mention previously, the data available period is quite different between the simulations, i.e. 70 years vs 100 years vs 18 years. This, to my opinion, can make it quite difficult to compare, any reason why you did not choose the same period for all experiments? How significant the differences or how sensitive the comparison would be if considered on similar periods? I believe more clarification is needed on this side.
Line 126: “GHG” has not been defined before as well as the different “TS” terms. Please make sure it is indicated in the text.
Line 127 and after: symbol ‘/’ is confusing as it is usually used for division in equations, please write the equations separately.
Line 339: “Possibly related to changes in sea ice”, don’t you have ice model as well in CCSM4 to back up this argument? It could be a nice addition. “possibly related” feels a bit weak and even more because the atmospheric resolution is different compared to the LRco2.
General Figure comments:
Figures 2 to 9 needs to be largely improved, the labels and ticks are very small and hard to read. Please add label for the y-axis on Figure 2 and 3.

Citation: https://doi.org/10.5194/egusphere-2023-340-RC2
- AC4:
  'Reply on RC2', Houraa Daher, 22 May 2023
  We appreciate the time and effort that the reviewer has dedicated to providing valuable feedback on our manuscript. We are grateful to the reviewer for their insightful comments on our study. We address their comments below and hope our response answers their concerns.
  We will add a more detailed description of the version of CCSM4 used in this study, including what land and ice models, to fit the scope of GMD.
  
  We do not include a comparison to other climate models as we only wanted to focus on the differences between other CCSM4 studies. But we can add a background about other climate models that have had a similar experimental setup.
  
  We agree that the changes the atmospheric resolution is not ideal but since previous existing experiments were set up like this we decided not to change it going forward. In response to this review we looked at another simulation that has constant year 2000 CO2 and O3 forcing and was run with 1 degree ocean and 0.5 degree atmosphere and compared this to our control experiment, LRC08 (1 degree ocean and 1 degree atmosphere) to determine the impact the change in atmospheric resolution has. We quickly looked at the zonal mean zonal wind, zonal mean zonal temperature, and sea surface temperature. With an increase in atmospheric resolution and keeping the ocean resolution at 1 degree, we find that there are warmer temperatures found near the equation and cooler temperatures in the lower stratosphere but not much of a difference elsewhere. For the zonal mean zonal wind, there are faster winds at the equator through all levels in the atmosphere. And for the sea surface temperatures, there is cooling observed around Antarctica. We do not have any additional experiments with this resolution and historical CO2 or 1955 O3 forcing to compare to our other experiments in this study, however. Because we find that the change in atmospheric resolution is indeed contributing some change to the variables looked at, we will fix the paper so it doesn’t solely focus on ocean resolution but also attributes the changes observed to both the ocean and atmospheric resolution since computationally we cannot rerun the experiments to have constant atmospheric resolution.
  
  The differences in data periods is due to what data was available for each experiment with HRC20 being the newest. But we did subset the data into shorter time intervals and didn’t find any significant differences
  
  We will add more to the results section explaining some of the physical processes occurring with the presence of eddies and the effects they can have on weakening the SST gradient, the SSH, and the temperature in the upper 1000 m of the ocean.
  
  Line 126: GHG needs to be corrected to CO2
  
  Line 127: The “/“ in the equations doesn’t represent a divide by rather a slash. We will fix this so it is no longer confusing and LRC and HRC will have their own equation
  
  Line 339: We will look into the effect the sea ice has on the surface temperature around Antarctica but found this pattern is similar to what was observed with the change atmospheric resolution mentioned above so this cooling could be due to the atmosphere.
  
  We will fix the figures and make the font bigger and make it easier to read.
  
  Thank you again for your comments.
  
  Citation: https://doi.org/10.5194/egusphere-2023-340-AC4

Status: closed

CEC1:
'Comment on egusphere-2023-340', Juan Antonio Añel, 06 Apr 2023

Dear authors,
Unfortunately, after checking your manuscript, it has come to our attention that it does not comply with our "Code and Data Policy".

https://www.geoscientific-model-development.net/policies/code_and_data_policy.html
The repositories that you mention in your "Code and data availability" section are not suitable for scientific publication. You must store your code and data in one of the suitable repositories listed in our policy. The repositories for code and data must be permanent, without the possibility of being deleted by the authors, accessible without limitations, and should have been available at the submission of your work. In fact, that your manuscript has been accepted for Discussions is an irregular situation and should not have happened.
Therefore, we will have to reject your manuscript unless you publish the code (CCSM4 model and modules and scripts that you use) in one of the appropriate repositories and reply to this comment with the relevant information (links and DOIs). Please, do it as soon as possible.
Also, please, remember that if you solve this with the necessary information in reply to this comment, you must include in any potentially reviewed version of your manuscript the modified 'Code and Data Availability' section with the information about the new repositories.
Juan A. Añel
Geosci. Model Dev. Executive Editor

Citation: https://doi.org/10.5194/egusphere-2023-340-CEC1
- AC1:
  'Reply on CEC1', Houraa Daher, 10 Apr 2023
  
  Dear Dr. Añel,
  The data and code used in this study has been uploaded to Zenodo and is openly available, complying with the GMD Code and Data Policy. Here is the DOI and link to the data and code.
  
  DOI: 10.5281/zenodo.7812531
  
  LINK: https://doi.org/10.5281/zenodo.7812531
  
  We will update the Code and Data Availability section in the manuscript in the potentially reviewed version we receive. Thank you.
  
  Best,
  
  Houraa Daher
  
  Citation: https://doi.org/10.5194/egusphere-2023-340-AC1
  - CEC2: 'Reply on AC1', Juan Antonio Añel, 13 Apr 2023
    
    Dear authors,
    Unfortunately, your reply does not fulfil our requirements. You have uploaded into the new repository files with output data and the scripts to analyze the data. However, we continue missing a repository for the code of the exact version of CCSM4 (and all their components (POP2, CAM-Chem, etc.)) that you use in your work.
    Therefore, your submission continues to violate our policy, and we will have to reject your manuscript unless you upload to a new repository the code requested. Please, reply to this comment with the details for the new repository.
    Juan A. Añel
    Geosci. Model Dev. Executive Editor
    
    Citation: https://doi.org/10.5194/egusphere-2023-340-CEC2
    
    AC2: 'Reply on CEC2', Houraa Daher, 17 Apr 2023
    
    Dear Dr. Añel,
    The CCSM4 code and ozone files have been uploaded to Zenodo as well and is available. The DOI and link to the code is below.
    DOI: 10.5281/zenodo.7838611
    Link: https://doi.org/10.5281/zenodo.7838611
    We will update the Code and Data Availability section accordingly. Thank you.
    
    Best,
    Houraa Daher
    
    Citation: https://doi.org/10.5194/egusphere-2023-340-AC2
RC1:
'Comment on egusphere-2023-340', Anonymous Referee #1, 10 May 2023
Review of “The impact of model resolution on the Southern Hemisphere in CCSM4 idealized climate simulations” by Houraa Daher and Ben P. Kirtman
General comments:
In this paper, the authors are examining the role of ocean model resolution on the Southern Hemisphere climate. They used the Community Climate System Model version 4 (CCSM4) to perform a suite of experiments by changing the ocean and atmospheric resolutions as well as CO₂ and O₃ forcing. This paper does not give any insights on the model development, and hence does not suit the journal Geoscientific Model Development. I have some reservations on their methods which I listed in detail below. Also, the analyses presented in the paper, in its present form, are too shallow to be published in a decent scientific journal. The authors may consider my detailed comments for revising the paper and submitting it to a more appropriate journal.
Specific comments:
The authors claim they investigate effect of ocean model resolution on the southern hemisphere climate simulated by a coupled model. However, they change the resolution of the atmospheric component as well. This is confusing. If the objective is to understand the role of ocean model resolution, then the resolution of the atmospheric model should be kept the same while changing the resolution of the ocean model. In a coupled model, the largest source of bias is the problems in simulating the effects of clouds. It depends on the atmospheric model resolution. There are plenty of works published on the cloud biases over the southern hemisphere oceans in CMIP5 coupled model experiments. These biases are more over the upwelling regions of the western boundaries due to the presence of a vast shallow cloud deck. I think that the upwelling also plays a role in these biases. When you change the ocean and atmosphere resolution simultaneously, it affects the simulations of ocean upwelling and atmospheric convection. This makes it difficult to attribute the changes in the simulated climate to the resolution of any particular model component. I see that there is a caveat in the text on the change in the atmospheric reolution. I would have accepted it if the focus of the paper was not on the impact of ocean model resolution.

Another issue is the duration of the experiments. The low-resolution simulations are performed for a longer period (100 years) while the high-resolution simulations are run for shorter durations (20 to 70 years). I suggest that all the experiments to be run for the same duration.

I had a hard time understanding the calculation of “net change”. In the equations (L130), did you divide LRC_co2 with HRC_co2? Does “/” mean “OR” in those equations?

Figures 2 – 9: I find it really difficult to read the labels due to small font sizes. More importantly, these analyses seem to be disconnected from each othere. Authors should present a coherent anaysis of the results. Also, I do not understand how these results help model developers.
Citation: https://doi.org/10.5194/egusphere-2023-340-RC1
- AC3:
  'Reply on RC1', Houraa Daher, 22 May 2023
  We appreciate the time and effort that the reviewer has dedicated to providing valuable feedback on our manuscript. We are grateful to the reviewer for their insightful comments on our study. We address their comments below and hope our response answers their concerns.
  We chose to submit to the model evaluation section of GMD because we are looking at how changes in the model resolution leads to different results in CCSM4 specifically rather than how this study can improve future model development.
  We agree that the changes the atmospheric resolution is not ideal but since previous existing experiments were set up like this we decided not to change it going forward. In response to this review we looked at another simulation that has constant year 2000 CO2 and O3 forcing and was run with 1 degree ocean and 0.5 degree atmospheric resolution and compared this to our control experiment, LRC08 (1 degree ocean and 1 degree atmosphere) to determine the impact the change in atmospheric resolution has. We quickly looked at the zonal mean zonal wind, zonal mean zonal temperature, and sea surface temperature. With an increase in atmospheric resolution and keeping the ocean resolution at 1 degree, we find that there are warmer temperatures found near the equation and cooler temperatures in the lower stratosphere but not much of a difference elsewhere. For the zonal mean zonal wind, there are faster winds at the equator through all levels in the atmosphere. And for the sea surface temperatures, there is cooling observed around Antarctica. We do not have any additional experiments with this resolution and historical CO2 or 1955 O3 forcing to compare to our other experiments in this study, however. Because we find that the change in atmospheric resolution is indeed contributing some change to the variables looked at, we will fix the paper so it doesn’t solely focus on ocean resolution but also attributes the changes observed to both the ocean and atmospheric resolution since computationally we cannot rerun the experiments to have constant atmospheric resolution.
  
  The reviewer brings up the issue of the duration of the experiments as the low resolution experiments are all 100 years and the high resolution experiments are between 20-70 years. The differences in data periods is due to what data was available for each experiment with HRC20 being the newest. We did subset our output in shorter time intervals and didn’t find any significant differences.
  
  The “/“ in the equations is signifying or not division. We will fix this in the manuscript so it is clearer and not confusing. There will be an equation for LRC and HRC for each of the forcing changes.
  
  We will improve the font size on the figures so they are easier to read. Additionally we will improve our results section so the figures shown are connected to each other.
  
  Thank you again for your comments.
  
  Citation: https://doi.org/10.5194/egusphere-2023-340-AC3
RC2:
'Comment on egusphere-2023-340', Anonymous Referee #2, 13 May 2023

Review: “The impact of model resolution on the Southern Hemisphere in CCSM4 idealized climate simulations” by Daher and Kirtman.

This manuscript investigates the impact of eddy-resolving versus eddy-parameterizing simulation in the Southern Hemisphere. Especially, the authors look at the climate response sensitivity to different CO2 concentration and ozone levels forcing using the CCSM4 community model to perform the experiments. They look at the differences induced in zonal mean atmospheric temperature, zonal mean zonal wind, sea surface temperature, sea surface height, eddy kinetic energy, zonal mean ocean temperature, convective precipitation and surface temperature. They found significant differences between low and high resolutions simulations induced by better modeling the mesoscale eddies. Moreover, they found that overall in eddy-resolving simulations the changes in CO2 concentration are more dominant, especially in eddy-rich regions, whereas in eddy-parameterization the changes in ozone levels are more dominant.
General comments and main concerns:
Overall, the paper is well written and easy to follow. For the scope of GMD I believe a more detailed description of the model used needs to be done and how novel this model comparison performance is in regard to literature or what is usually done in climate models. There are some caveats in the methodology which are for the most part addressed by the authors, like the changes in atmospheric resolution. However, this can cause significant differences in the results, I would suggest to run the simulations on the same atmospheric resolution to be very clear on the actual impact of the ocean resolution only which is the goal of this paper. Moreover, some changes in methodology like de data periods differences between simulations are not addressed and thus can be confusing when looking at the results presented. Overall, the results section is very descriptive and just show differences but don’t really explain any of them. A deeper or more thorough analysis of the results and changes observed would be needed. Indeed, it is expected that a change in resolution would produce different results but we need to know why and why the results would be better, at least here in term of physical processes representation as the simulations are very idealized. I believe the paper in present form would need more work to be suitable for publication.
Some specific comments:
Around line 80: The model description that has been used needs to be much more detailed than what it is right now, some key parametrizations used, land model, ice model, coupler…
Around line 95: When describing the different experiments, it could be clearer to define the control experiment first and then the idealized simulations and thus what the comparison to the control experiments would mean.
Line 92 and 104: As mention previously, the data available period is quite different between the simulations, i.e. 70 years vs 100 years vs 18 years. This, to my opinion, can make it quite difficult to compare, any reason why you did not choose the same period for all experiments? How significant the differences or how sensitive the comparison would be if considered on similar periods? I believe more clarification is needed on this side.
Line 126: “GHG” has not been defined before as well as the different “TS” terms. Please make sure it is indicated in the text.
Line 127 and after: symbol ‘/’ is confusing as it is usually used for division in equations, please write the equations separately.
Line 339: “Possibly related to changes in sea ice”, don’t you have ice model as well in CCSM4 to back up this argument? It could be a nice addition. “possibly related” feels a bit weak and even more because the atmospheric resolution is different compared to the LRco2.
General Figure comments:
Figures 2 to 9 needs to be largely improved, the labels and ticks are very small and hard to read. Please add label for the y-axis on Figure 2 and 3.

Citation: https://doi.org/10.5194/egusphere-2023-340-RC2
- AC4:
  'Reply on RC2', Houraa Daher, 22 May 2023
  We appreciate the time and effort that the reviewer has dedicated to providing valuable feedback on our manuscript. We are grateful to the reviewer for their insightful comments on our study. We address their comments below and hope our response answers their concerns.
  We will add a more detailed description of the version of CCSM4 used in this study, including what land and ice models, to fit the scope of GMD.
  
  We do not include a comparison to other climate models as we only wanted to focus on the differences between other CCSM4 studies. But we can add a background about other climate models that have had a similar experimental setup.
  
  We agree that the changes the atmospheric resolution is not ideal but since previous existing experiments were set up like this we decided not to change it going forward. In response to this review we looked at another simulation that has constant year 2000 CO2 and O3 forcing and was run with 1 degree ocean and 0.5 degree atmosphere and compared this to our control experiment, LRC08 (1 degree ocean and 1 degree atmosphere) to determine the impact the change in atmospheric resolution has. We quickly looked at the zonal mean zonal wind, zonal mean zonal temperature, and sea surface temperature. With an increase in atmospheric resolution and keeping the ocean resolution at 1 degree, we find that there are warmer temperatures found near the equation and cooler temperatures in the lower stratosphere but not much of a difference elsewhere. For the zonal mean zonal wind, there are faster winds at the equator through all levels in the atmosphere. And for the sea surface temperatures, there is cooling observed around Antarctica. We do not have any additional experiments with this resolution and historical CO2 or 1955 O3 forcing to compare to our other experiments in this study, however. Because we find that the change in atmospheric resolution is indeed contributing some change to the variables looked at, we will fix the paper so it doesn’t solely focus on ocean resolution but also attributes the changes observed to both the ocean and atmospheric resolution since computationally we cannot rerun the experiments to have constant atmospheric resolution.
  
  The differences in data periods is due to what data was available for each experiment with HRC20 being the newest. But we did subset the data into shorter time intervals and didn’t find any significant differences
  
  We will add more to the results section explaining some of the physical processes occurring with the presence of eddies and the effects they can have on weakening the SST gradient, the SSH, and the temperature in the upper 1000 m of the ocean.
  
  Line 126: GHG needs to be corrected to CO2
  
  Line 127: The “/“ in the equations doesn’t represent a divide by rather a slash. We will fix this so it is no longer confusing and LRC and HRC will have their own equation
  
  Line 339: We will look into the effect the sea ice has on the surface temperature around Antarctica but found this pattern is similar to what was observed with the change atmospheric resolution mentioned above so this cooling could be due to the atmosphere.
  
  We will fix the figures and make the font bigger and make it easier to read.
  
  Thank you again for your comments.
  
  Citation: https://doi.org/10.5194/egusphere-2023-340-AC4

Houraa Daher and Ben P. Kirtman

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Total article views: 584 (including HTML, PDF, and XML)

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PDF: 130
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EndNote: 12

Views and downloads (calculated since 07 Mar 2023)

Month	HTML	PDF	XML	Total
Mar 2023	137	33	7	177
Apr 2023	126	23	8	157
May 2023	52	11	8	71
Jun 2023	13	4	0	17
Jul 2023	17	13	3	33
Aug 2023	25	5	1	31
Sep 2023	19	12	0	31
Oct 2023	4	6	0	10
Nov 2023	1	3	1	5
Dec 2023	2	3	0	5
Jan 2024	1	2	0	3
Feb 2024	4	4	0	8
Mar 2024	16	11	1	28
Apr 2024	6	2	8

Cumulative views and downloads (calculated since 07 Mar 2023)

Month	HTML	PDF	XML	Total
Mar 2023	137	33	7	177
Apr 2023	126	23	8	157
May 2023	52	11	8	71
Jun 2023	13	4	0	17
Jul 2023	17	13	3	33
Aug 2023	25	5	1	31
Sep 2023	19	12	0	31
Oct 2023	4	6	0	10
Nov 2023	1	3	1	5
Dec 2023	2	3	0	5
Jan 2024	1	2	0	3
Feb 2024	4	4	0	8
Mar 2024	16	11	1	28
Apr 2024	6	2	8

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Total article views: 581 (including HTML, PDF, and XML) Thereof 581 with geography defined and 0 with unknown origin.

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Latest update: 26 Apr 2024

Short summary

This study looks at the effect ocean model resolution has on the Southern Hemisphere climate using data from a global climate model. Low resolution and high resolution data are used to observe changes and the CO₂ concentrations and ozone are varied to determine which is more important. In the low resolution data, the ozone is found to be more important than the CO₂ concentrations. The opposite is seen for the high resolution data with the CO₂ concentrations being more dominant than the ozone.


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