Technical descriptions of the experimental dynamical downscaling simulations over North America by the CAM–MPAS variable-resolution model

Sakaguchi, Koichi; Leung, L. Ruby; Zarzycki, Colin M.; Jang, Jihyeon; McGinnis, Seth; Harrop, Bryce E.; Skamarock, William C.; Gettelman, Andrew; Zhao, Chun; Gutowski, William J.; Leak, Stephen; Mearns, Linda

doi:https://doi.org/10.5194/gmd-16-3029-2023

Articles | Volume 16, issue 10

https://doi.org/10.5194/gmd-16-3029-2023

© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/gmd-16-3029-2023

© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 16, issue 10

Model evaluation paper

|

01 Jun 2023

Model evaluation paper |

| 01 Jun 2023

Technical descriptions of the experimental dynamical downscaling simulations over North America by the CAM–MPAS variable-resolution model

Koichi Sakaguchi, L. Ruby Leung, Colin M. Zarzycki, Jihyeon Jang, Seth McGinnis, Bryce E. Harrop, William C. Skamarock, Andrew Gettelman, Chun Zhao, William J. Gutowski, Stephen Leak, and Linda Mearns

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Final revised paper (published on 01 Jun 2023)
Preprint (discussion started on 09 Jan 2023)

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2022-1199', Anonymous Referee #1, 10 Feb 2023

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2022-1199/egusphere-2022-1199-RC1-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2022-1199-RC1
- AC1: 'Reply on RC1', Koichi Sakaguchi, 07 Mar 2023
  
  Thank you very much for your time and constuctive suggestions. The suggestions are very helpful, espesically those for Figure 2 where we explain the coupling between CAM and MPAS, organization of the model experiment section, and appendix tables where we found several mistakes.
  I have made draft changes to incorporate the comments and shared them with my co-authors. We look forward to uploading the revised version and formal reply to you after the discussion period ends.
  Best,
  Koichi
  
  Citation: https://doi.org/10.5194/egusphere-2022-1199-AC1
RC2:
'Comment on egusphere-2022-1199', Anonymous Referee #2, 17 Mar 2023

This paper provides a comprehensive overview of new global climate model simulation using CAM5.4-MPAS4.0 and variable-resolution grid.
Key features of the paper include:

* Thorough description of the modeling system and variable grid structure.

* Detailed outline of simulation protocol for pseudo global warming experiments.

* Evaluation of computational performance of various variable and fixed grids.

* Overview of the simulated current and future climates from one of the variable-grid experiments.
These experiments are innovative and explore several important and emerging issues in climate modeling. As a technical paper describing these methods and results, I find the paper well written and comprehensive. I recommend publication.
Reading with an eye to how one might use these simulations, I feel there are several issues with the experimental protocol that are not adequately addressed. These issues may be better explored in subsequent research, but I feel they need to be raised here. Primarily, there are many elements being varied among the simulations compared so it is difficult to assess which is responsible for the results. A couple examples:
1) The global precipitation increases with model resolution is not intuitive and is made more complex do to tuning of the convective scheme.
2) The delta SST is taken from MPI and may not be consistent with the circulation shift seen in the free-running CAM model.

Citation: https://doi.org/10.5194/egusphere-2022-1199-RC2
- AC2: 'Reply on RC2', Koichi Sakaguchi, 17 Mar 2023
  
  Thank you very much for reading through our manuscript. We appreciate your feedback with the two specific points.
  We agree that resolution-sensitivity of modeled precipitation is quite complex, and will state that drawing denitive conclution about the underlying mechanisms (including the tuning of convection parameterization) requires more systematic experiments.
  The second point is a great point that I (lead author) did not think about. If I understand correctly, possible incosistency referred to by reviewer #2 arises from our simulations being an uncoupled atmosphere-only run and using SST & delta T derived from a different climate model & reanalysis, rather than from the fully coupled version of the same CESM (CAM-MPAS) model. My current thinking is that as the atmosphere-only CAM responds to a prescribed SST pattern, the simulated response itself is physically consistent to the extent CAM reproduces the real atmosphere, but again without feeding back to the ocean circulation. This point is probably more relevant to global VR models than to regional climate models. We will mention this second point in the revised manuscript as well, most likely in the section 5.2.2 Future Climate section (I will give it more thoughts and discuss with co-authors) .
  Best regards,
  Koichi
  
  Citation: https://doi.org/10.5194/egusphere-2022-1199-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Koichi Sakaguchi on behalf of the Authors (30 Mar 2023) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (13 Apr 2023) by Sophie Valcke

AR by Koichi Sakaguchi on behalf of the Authors (17 Apr 2023) Author's response Author's tracked changes Manuscript

ED: Publish as is (19 Apr 2023) by Sophie Valcke

AR by Koichi Sakaguchi on behalf of the Authors (20 Apr 2023)

Short summary

We document details of the regional climate downscaling dataset produced by a global variable-resolution model. The experiment is unique in that it follows a standard protocol designed for coordinated experiments of regional models. We found negligible influence of post-processing on statistical analysis, importance of simulation quality outside of the target region, and computational challenges that our model code faced due to rapidly changing super computer systems.