ICON-HAM-lite: simulating the Earth system with interactive aerosols at kilometer scales

Weiss, Philipp; Herbert, Ross; Stier, Philip

doi:https://doi.org/10.5194/egusphere-2024-3325

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https://doi.org/10.5194/egusphere-2024-3325

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30 Oct 2024

| 30 Oct 2024

ICON-HAM-lite: simulating the Earth system with interactive aerosols at kilometer scales

Philipp Weiss, Ross Herbert, and Philip Stier

Abstract. Aerosols strongly influence Earth's climate as they scatter and absorb radiation and serve as condensation nuclei for cloud droplets and ice particles. New Earth system models that run at kilometer resolutions allow us to examine long-standing questions related to these interactions. To perform kilometer-scale simulations with the Earth system model ICON-MPIM, we developed the one-moment aerosol module HAM-lite. HAM-lite was derived from the two-moment module HAM. Like in HAM, aerosols are represented as an ensemble of log-normal modes. Unlike in HAM, aerosol sizes and compositions are prescribed, which reduces the computational costs significantly. Here, we present a first global simulation with four aerosol modes at a resolution of five kilometers and over a period of one year. The simulation captured key aerosol processes including, for example, the emission of dust aerosols by convective storms in the Sahara and the interactions between sea salt aerosols and tropical cyclones in the Pacific.

Received: 24 Oct 2024 – Discussion started: 30 Oct 2024

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Philipp Weiss, Ross Herbert, and Philip Stier

Status: final response (author comments only)

CEC1:
'Comment on egusphere-2024-3325 - No compliance with the policy of the journal', Juan Antonio Añel, 08 Dec 2024

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

You have failed to comply with our policy regarding several issues. First, our policy establishes that "model description papers" must include a version number in the title of the manuscript. The topical Editor of your manuscript already pointed this out, but the manuscript is in Discussions without including it.
Second, you have archived your code on a Git version control site. However, Git sites are unsuitable for scientific publication; our policy mentions it, as they do not comply with the minimum requirements for scientific publication (long-term archival, impeding the removal of contents, permanent identifier).

Also, you do not provide the necessary access to the model you use for your work when our policy establishes that all the code and data used in a submitted manuscript must be available at submission time in one of the permanent repositories that we accept, with a DOI and without limitations, such as the need to register, contact authors, etc. Moreover, as the ICON model has been free since January 2024, there is no justification for not publishing it.
The irregularities in your manuscript are of significant concern. Manuscripts that do not adhere to our policy can not be accepted for Discussions, and unfortunately, your submission falls short on several key points. Therefore, please, I request that, as soon as possible, publish the code and data that you have used or produced and relevant to your manuscript in one of the appropriate repositories listed in our policy and reply to this comment with the relevant information (link and a permanent identifier for it (e.g. DOI)). Also, you must address the issue with the title replying to this comment with a new one that includes the version number of the model. Also, you must include a modified 'Code and Data Availability' section and the new title in a potentially reviewed manuscript.
If these issues are not addressed, we will be left with no choice but to reject your manuscript for publication in our journal.
Juan A. Añel

Geosci. Model Dev. Executive Editor

Citation: https://doi.org/10.5194/egusphere-2024-3325-CEC1
- AC1:
  'Reply on CEC1', Philipp Weiss, 11 Dec 2024
  
  Dear Chief editor
  Many thanks for your comment.
  To comply with the policies of your journal, we published the source code that we used to perform the simulation and the data and scripts that we used to generate the figures on Zenodo.
  Code and data availability:
  
  The source code that we used to perform the simulation is available on Zenodo (https://doi.org/10.5281/zenodo.14335069). The data and scripts that we used to generate the figures are available on Zenodo as well (https://doi.org/10.5281/zenodo.14393773).
  The title of the manuscript already contains a version number (https://egusphere.copernicus.org/preprints/2024/egusphere-2024-3325/egusphere-2024-3325.pdf). We revised the title after the initial iteration with the handling editor.
  Title:
  
  ICON-HAM-lite 1.0: simulating the Earth system with interactive aerosols at kilometer scales
  Please let us know, as soon as possible, if we need to make further revisions.
  Best wishes, Philipp Weiss
  
  Citation: https://doi.org/10.5194/egusphere-2024-3325-AC1
  - CEC2: 'Reply on AC1', Juan Antonio Añel, 12 Dec 2024
    
    Dear authors,
    Thanks for addressing the issues raised so quickly. Regarding the model version number in the title of the manuscript, apologies, as I overlooked that in the PDF file it is included.
    We can now consider the current version of your manuscript compliant with our code and data policy.
    Juan A. Añel
    Geosci. Model Dev. Executive Editor
    
    Citation: https://doi.org/10.5194/egusphere-2024-3325-CEC2
RC1:
'Comment on egusphere-2024-3325', Anonymous Referee #1, 09 Dec 2024
Review of ICON-HAM-lite: simulating the Earth system with interactive aerosols at kilometer scales:

General Comments:
1) Does the paper address relevant scientific modelling questions within the scope of GMD? Does the paper present a model, advances in modelling science, or a modelling protocol that is suitable for addressing relevant scientific questions within the scope of EGU?
Yes. A new modal aerosol model is developed for use in sub-10 km chemistry transport modeling.
2) Does the paper present novel concepts, ideas, tools, or data?
Yes. HAM-lite is a novel adaptation of HAM.
3) Does the paper represent a sufficiently substantial advance in modelling science?
Yes. The authors demonstrate the applicability of HAM-lite for high resolution modeling.
4) Are the methods and assumptions valid and clearly outlined?
Yes, but with a caveat. The authors describe their model experiment sufficiently. But more information should be given about the performance of HAM-lite compared to HAM.
5) Are the results sufficient to support the interpretations and conclusions?
Yes. The model output is evaluated comprehensively and clearly.
6) Is the description sufficiently complete and precise to allow their reproduction by fellow scientists (traceability of results)? In the case of model description papers, it should in theory be possible for an independent scientist to construct a model that, while not necessarily numerically identical, will produce scientifically equivalent results. Model development papers should be similarly reproducible. For MIP and benchmarking papers, it should be possible for the protocol to be precisely reproduced for an independent model. Descriptions of numerical advances should be precisely reproducible.
Yes. The model experiment presented in the paper can be reproduced using the same model and inputs by other authors and can also be approximated by other models making similar parameterization choices and using similar emissions and surface data (SSTs and sea ice).
7) Do the authors give proper credit to related work and clearly indicate their own new/original contribution?
Yes. All relevant input for this paper is cited and original contribution clearly delineated.
8) Does the title clearly reflect the contents of the paper? The model name and number should be included in papers that deal with only one model.
Yes and no. The model version numbers are missing but the title properly describes the paper contents.
9) Does the abstract provide a concise and complete summary?
Yes.
10) Is the overall presentation well structured and clear?
Yes. But more content needs to be included as outlined in the Specific Comments.
11) Is the language fluent and precise?
Yes.
12) Are mathematical formulae, symbols, abbreviations, and units correctly defined and used?
Yes.
13) Should any parts of the paper (text, formulae, figures, tables) be clarified, reduced, combined, or eliminated?
No.
15) Are the number and quality of references appropriate?
Yes.
15) Is the amount and quality of supplementary material appropriate? For model description papers, authors are strongly encouraged to submit supplementary material containing the model code and a user manual. For development, technical, and benchmarking papers, the submission of code to perform calculations described in the text is strongly encouraged.
N/A.

Specific Comments:
1) This model lacks secondary aerosol formation (sulfate and SOA) and this should be explicitly mentioned in the model description. Lack of secondary aerosol affects the optical depth (Figure 6). The authors attribute the deviation from MODIS observations to primary emissions issues on page 13.   This is only partially valid. Lack of SOA in the model has a large impact on the carbonaceous aerosol simulated.   AeroCom models compared in Table 5 included SOA schemes. SOA accounts for more than half of organic aerosol globally. There is no mention of secondary aerosol anywhere in the manuscript.   The paper needs to be revised to outline this model limitation and its impact on comparison with observations.
2) The resolution of 5 km is not sufficient to resolve convective updrafts and downdrafts which for deep convection have a diameter under 3 km over land and under 1 km over the oceans. Shallow convection is even smaller in scale.    Instead of trying to run with a compromise resolution globally, a better approach would have been to use a high-resolution regional domain driven by boundary conditions form a coarser resolution global run.   The authors should include more discussion about their choice of the 5 km resolution. Using the term “kilometer scale” to describe a 5 km resolution is not valid even though this has become a widely used term.    This resolution does not have the dynamical process resolving power of 2 km let alone 1 km.
The 5 km resolution is in a transition or gray zone between the need for parameterized deep convection at 10 km and relatively reasonably resolved deep convection over land at 2 km. It is possible to apply a scale-ware deep convection scheme at transition zone resolutions (https://doi.org/10.1029/2021MS002696) since resolved convection is inadequate. In terms of the smaller scale shallow convection, which is important for tracer transport, the 5 km resolution requires use of a parameterization scheme (https://doi.org/10.1175/MWR-D-19-0030.1).

The 5 km resolution is not good enough to reject using a 10 km resolution and assuming hydrostatic conditions with deep and shallow convective parameterizations.   This would have the benefit of being able to run with a 5-minute timestep instead of 40 seconds.   More resources could be expended on aerosol process representation.    In spite of progress in computer speed we are still not at the stage of running global cloud resolving models even with highly simplified chemistry and aerosol processes.

3) There is no evaluation of the HAM-lite model against the original HAM cited. Comparison of the two schemes for test cases on small domains would give insight into the biases introduced by the simplifications in HAM-lite.   It is not particularly clear from the paper how HAM-lite parameters were tuned. This subject is work for another paper, but the authors should include more discussion about how HAM-lite compares to HAM in terms of predicted aerosol distributions and how HAM-Lite parameters were selected.

Technical Comments:
L104: Replace reference with Tegen et al. (2002): DOI: 10.1029/2001JD000963
L183: Correct spelling of asymmetry.
Citation: https://doi.org/10.5194/egusphere-2024-3325-RC1
RC2: 'Comment on egusphere-2024-3325', Stefan Kinne, 22 Dec 2024

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-3325/egusphere-2024-3325-RC2-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2024-3325-RC2
RC3:
'Comment on egusphere-2024-3325', Anonymous Referee #3, 30 Dec 2024
The manuscript “ICON-HAM-lite 1.0: simulating the Earth system with interactive aerosols at kilometer scales” by Weiss et al. presents a new simplified aerosol scheme that allows to run global interactive aerosol simulations at km-scale grid spacings. The authors explain the implementation of the scheme and its interaction with the other physics schemes and show results from a yearlong simulation at 5 km horizontal grid spacing. The results show that the model can capture aerosol properties similarly well as state-of-the-art models and compares reasonable well compared to observations although systematic biases seem to exist. The emergence of mesoscale details such as dust storms on the leading edge of cold pools is particularly encouraging since such features have not been able to simulate at global scales so far. The paper is well written, and the images are of high quality. My only major comment is that adding some kind of comparison to the original ICON HAM model and a discussion about the differences would be important. The main question to answer here would be what the HAM-lite model cannot do what the more complex HAM model can and how does this affect the simulations and the ability to answer science questions. More details on this topic and a few more specific comments can be found below.
General Comments:
You mention that it would be too expensive to run the two-moment module HAM with 5 km grid spacing but I was hoping to see an intercomparison between the original HAM and HAM-lite even if it is only at 10 km or for a short period of time. Such a comparison would shed some light on the differences and potential implications of the simpler scheme and might also help to improve HAM-light. I understand that adding such a comparison would be a lot of work but would also bring a lot of benefits. If you decide to not work on this, I recommend to at least discuss potential differences and work on a comparison in the near future.

Related to the above comment; Could you add a discussion on what the systematic impacts of using a single moment aerosol representation are? What processes would be better captured using a two-moment representation and where should users be careful when using the one moment output for process understanding?

Specific comments:
L19: Do CMIP6 type models truly have complex microphysics compared to e.g., modern weather forecasting models. My impression was that they usually use single moment schemes without graupel/hail. Additionally, running deep convection schemes that produce precipitation complicates things.
L84-5: Currently this reads like there are three schemes for microphysics, radiation, and turbulence each. You could write: "There are three parameterization schemes, one for cloud microphysics, one for radiation, and one for turbulence..."
L109: "To forward emissions to modes,..." what is meant here? Please reformulate.
L259-60: I do not see anything special at 500 hPa in the dust concentration profiles. It seems as if the peak of emissions is related to the height of the source region (e.g. dust emissions over the Tibetan Plateau should be around 600 hPa). Plotting the profiles regarding height above surface should help to reduce this effect.
L269-70: I appreciate that you mention satellite observation uncertainties. Could you add a sentence on how those might affect this comparison?
L296: "The vertical velocities highlight diverging cold pool edges that lift air from convective downdrafts." This should probably be something like: ... diverging cold pools that originate from convective downdrafts and mesoscale circulation that lifts air at the gust front.
L299-300: It is not only the cold pools that are not captured but also the mesoscale circulation (e.g., mesocyclones, rear-inflow jets in MCSs...). One study that discusses this is:

Prein, A.F., 2023. Thunderstorm straight line winds intensify with climate change. Nature Climate Change, 13(12), pp.1353-1359.
Citation: https://doi.org/10.5194/egusphere-2024-3325-RC3

Philipp Weiss, Ross Herbert, and Philip Stier

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Short summary

Aerosols strongly influence Earth's climate as they interact with radiation and clouds. New Earth system models run at resolutions of a few kilometers. To simulate the Earth system with interactive aerosols, we developed a new aerosol module. It represents aerosols as an ensemble of log-normal modes with given sizes and compositions. We present a year-long simulation with four modes at a resolution of five kilometers. It captures key aerosol processes like dust storms or tropical cyclones.


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