the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 30 Nov 2023
Developing a climatological simplification of aerosols to enter the cloud microphysics of a global climate model
Abstract. Aerosol particles influence cloud formation and properties. Hence climate models that aim for a physical representation of the climate system include aerosol modules. In order to represent more and more processes and aerosol species, their representation has grown increasingly detailed. However, depending on one's modeling purpose, the increased model complexity may not be beneficial, for example because it hinders understanding of model behaviour. Hence we develop a simplification in the form of a climatology of aerosol concentrations. In one approach, the climatology prescribes properties important for cloud droplet and ice crystal formation, the gateways for aerosols to enter the model cloud microphysics scheme. Another approach prescribes aerosol mass and number concentrations in general. Both climatologies are derived from full ECHAM-HAM simulations and can serve to replace the HAM aerosol module and thus drastically simplify the aerosol treatment. The first simplification reduces computational model time by roughly 65 %. However, the naive mean climatological treatment needs improvement to give results that are satisfyingly close to the full model. We find that mean CCN concentrations yield an underestimation of CDNC in the Southern Ocean, which we can reduce by allowing only CCN at cloud base (which have experienced hygroscopic growth in these conditions) to enter the climatology. This highlights the value of the simplification approach in pointing to unexpected model behaviour and providing a new perspective for its study and model development.
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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
(20921 KB)
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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
(20921 KB) - Metadata XML
- BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-2783', Anonymous Referee #1, 03 Jan 2024
I would like to provide some feedback on the authors' statement regarding the application of CCN/INPclim to replace HAM, resulting in "surprisingly equifinal results to a full ECHAM-HAMMOZ simulation." While I appreciate the study, I have concerns about the term "equifinal" given the observed relative variation of CDNC close to 20%, which, in my perspective, can be considered quite substantial. To ensure clarity, it would be beneficial to explicitly illustrate these relative differences, perhaps through the use of Figures 1-2.
Moreover, the information presented in Figure B2 highlights relative differences in CDND over the Southern Ocean ranging from -0.50 to -0.25. These variations are comparable to those induced by the replacement of microphysics schemes (e.g., replacing MG2 with P3). Consequently, it prompts the need for a thorough evaluation of whether the simplified aerosol treatment is scientifically justifiable.
While the authors assert that a simple aerosol treatment will not significantly alter cloud properties such as cloud radiative forcing and LWP, it is imperative to ensure that the effective forcing of anthropogenic aerosols remains unaffected. Furthermore, I suggest paying close attention to the accuracy of the historical simulation of surface temperature anomalies. In essence, a more comprehensive effort is warranted to ascertain that the adoption of simple aerosol treatments does not have adverse effects on the estimation of aerosol radiative effects and historical simulations.
I appreciate your understanding and consideration of these points as the study progresses. Thank you for your diligence in addressing these concerns.
Citation: https://doi.org/10.5194/egusphere-2023-2783-RC1 - AC1: 'Reply on RC1 and RC2', Ulrike Proske, 23 Feb 2024
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RC2: 'Comment on egusphere-2023-2783', Anonymous Referee #2, 03 Jan 2024
Climatologies of aerosols for the ECHAM-HAM model are presented, motivated by the need for more interpretability. This is important and useful work and complements other efforts to simplify the aerosol microphysics such as HAMlite and MACv2-SP. An interesting analysis of the potential challenges of the simpler climatology approaches for CCN in humid conditions near cloud base is presented. The more complex aerosol climatology roughly maintains aerosol forcing and climate sensitivity as in the default model (at least, as it is calculated by the authors) while the simpler CCN/IN climatology does not maintain forcing: it’s useful to see that some simplification can be achieved with minimal loss of ‘equifinality’ while more simplification, while still useful in some situations, does degrade key performance metrics. The paper is well written.
Minor comment
In Figure 5 it would be helpful to show observations from CERES level 3 data, or from (for example) the Grosvenor et al CDNC dataset, to put the differences between the models in context of the difference between models and observations. Or simply state the typical scale of model-observation discrepancies (likely > 25% in many regions for CDNC at least, I imagine) to give this context, and also provide context to the discussion around line 455.
Editorial comments
The text in Figure 2 is too small.
Would be useful to include a sentence explaining why sections 2.1-2.4 are important to the paper – just a statement that these parameterizations are the ones that relate aerosols to clouds and/or differ between the simulations presented would suffice.
Fig 5 caption needs to define ‘mxpT’ and ‘cold’
L429 believes->beliefs
The discussion of the relative merits of different possible simplification approaches is more appropriate in the introduction than in the summary; I suggest the authors move lines 431-442 to the introduction.
Citation: https://doi.org/10.5194/egusphere-2023-2783-RC2 - AC1: 'Reply on RC1 and RC2', Ulrike Proske, 23 Feb 2024
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-2783', Anonymous Referee #1, 03 Jan 2024
I would like to provide some feedback on the authors' statement regarding the application of CCN/INPclim to replace HAM, resulting in "surprisingly equifinal results to a full ECHAM-HAMMOZ simulation." While I appreciate the study, I have concerns about the term "equifinal" given the observed relative variation of CDNC close to 20%, which, in my perspective, can be considered quite substantial. To ensure clarity, it would be beneficial to explicitly illustrate these relative differences, perhaps through the use of Figures 1-2.
Moreover, the information presented in Figure B2 highlights relative differences in CDND over the Southern Ocean ranging from -0.50 to -0.25. These variations are comparable to those induced by the replacement of microphysics schemes (e.g., replacing MG2 with P3). Consequently, it prompts the need for a thorough evaluation of whether the simplified aerosol treatment is scientifically justifiable.
While the authors assert that a simple aerosol treatment will not significantly alter cloud properties such as cloud radiative forcing and LWP, it is imperative to ensure that the effective forcing of anthropogenic aerosols remains unaffected. Furthermore, I suggest paying close attention to the accuracy of the historical simulation of surface temperature anomalies. In essence, a more comprehensive effort is warranted to ascertain that the adoption of simple aerosol treatments does not have adverse effects on the estimation of aerosol radiative effects and historical simulations.
I appreciate your understanding and consideration of these points as the study progresses. Thank you for your diligence in addressing these concerns.
Citation: https://doi.org/10.5194/egusphere-2023-2783-RC1 - AC1: 'Reply on RC1 and RC2', Ulrike Proske, 23 Feb 2024
-
RC2: 'Comment on egusphere-2023-2783', Anonymous Referee #2, 03 Jan 2024
Climatologies of aerosols for the ECHAM-HAM model are presented, motivated by the need for more interpretability. This is important and useful work and complements other efforts to simplify the aerosol microphysics such as HAMlite and MACv2-SP. An interesting analysis of the potential challenges of the simpler climatology approaches for CCN in humid conditions near cloud base is presented. The more complex aerosol climatology roughly maintains aerosol forcing and climate sensitivity as in the default model (at least, as it is calculated by the authors) while the simpler CCN/IN climatology does not maintain forcing: it’s useful to see that some simplification can be achieved with minimal loss of ‘equifinality’ while more simplification, while still useful in some situations, does degrade key performance metrics. The paper is well written.
Minor comment
In Figure 5 it would be helpful to show observations from CERES level 3 data, or from (for example) the Grosvenor et al CDNC dataset, to put the differences between the models in context of the difference between models and observations. Or simply state the typical scale of model-observation discrepancies (likely > 25% in many regions for CDNC at least, I imagine) to give this context, and also provide context to the discussion around line 455.
Editorial comments
The text in Figure 2 is too small.
Would be useful to include a sentence explaining why sections 2.1-2.4 are important to the paper – just a statement that these parameterizations are the ones that relate aerosols to clouds and/or differ between the simulations presented would suffice.
Fig 5 caption needs to define ‘mxpT’ and ‘cold’
L429 believes->beliefs
The discussion of the relative merits of different possible simplification approaches is more appropriate in the introduction than in the summary; I suggest the authors move lines 431-442 to the introduction.
Citation: https://doi.org/10.5194/egusphere-2023-2783-RC2 - AC1: 'Reply on RC1 and RC2', Ulrike Proske, 23 Feb 2024
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Cited
Sylvaine Ferrachat
Ulrike Lohmann
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(20921 KB) - Metadata XML