A Lagrangian particle tracking framework for the  super-droplet method in SCALE-SDM 5.2.6-2.3.1:  implementation and computational evaluation

Yin, Chongzhi; Shima, Shin-Ichiro; Lu, Chunsong

doi:10.5194/gmd-19-9993-2026

Articles | Volume 19, issue 20

https://doi.org/10.5194/gmd-19-9993-2026

© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/gmd-19-9993-2026

© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 19, issue 20

Development and technical paper

|

20 Oct 2026

Development and technical paper |

| 20 Oct 2026

A Lagrangian particle tracking framework for the super-droplet method in SCALE-SDM 5.2.6-2.3.1: implementation and computational evaluation

Chongzhi Yin, Shin-Ichiro Shima, and Chunsong Lu

Download

Final revised paper (published on 20 Oct 2026)
Preprint (discussion started on 18 Dec 2025)

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-6221', Clara Bayley, 24 Feb 2026

Please see the attachment.

Citation: https://doi.org/10.5194/egusphere-2025-6221-RC1
- AC1: 'Reply on RC1', Chongzhi Yin, 19 Jun 2026
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-6221/egusphere-2025-6221-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2025-6221-AC1
RC2:
'Comment on egusphere-2025-6221', Anonymous Referee #2, 13 Mar 2026

Please refer to the attached reviwer`s comment

Citation: https://doi.org/10.5194/egusphere-2025-6221-RC2
- AC2: 'Reply on RC2', Chongzhi Yin, 19 Jun 2026
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-6221/egusphere-2025-6221-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2025-6221-AC2

Peer review completion

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

AR by Chongzhi Yin on behalf of the Authors (19 Jun 2026) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (23 Jul 2026) by Yang Tian

RR by Clara Bayley (04 Aug 2026)

Suggestions for revision or reasons for rejection

Dear Authors,

Having read your revised manuscript it appears to be almost entirely re-written. Whilst this has no doubt improved the content and framing, it does also make it somewhat more difficult for me to assess if my comments on the original manuscript have been fully addressed and I am unsure how to evaluate the entirely new content, namely the Two-Pass Hybrid Tracking. For these reasons, I recommend this manuscript be reconsidered after major revisions.

*Major comments:*

- The title is improved but perhaps slightly irregular, why is TPHT mentioned whereas forward and backward tracking are not? Perhaps simply “implementation and computational evaluation” is sufficient.

- I appreciate that you have re-written the abstract with my previous comments in mind, however the new version is jargon heavy and therefore difficult to understand. I think it serves the purpose of summarising the manuscript well, but only after having read the revised manuscript to understand what all the words mean. Consider using simpler language and explaining any new terms, for example: “shared target-selection”, “sampling subsystem”, “forward discovery pass”, “backward reconstruction pass”, “deduplicated handoff”, “target discovery”, “coalescence-event context”, “target-set diagnostics” and “predecessor-chain reconstruction”.

- I commend the authors for the new computational analyses included in the appendices of the manuscript. They have addressed most of my concerns regarding the computational evaluation. I have three (small) remaining comments:
-- You may consider moving the analyses into the main text since they are heavily referenced in Section 3.2.3.
-- It would also be more informative for some metrics in Appendix A to be included which are normalised per superdroplet or per simulated-time-step (e.g. for the wall-clock time and output size).
-- With regards to the “superdroplet scaling” in Appendix C it may be beneficial to measure the scaling as the fraction of tracked superdroplets increases (i.e. from 5% to 10% to 20% etc.) rather than the total number of superdroplets in the domain, or perhaps it can be explained why the scaling would behave similarly in both cases.

- Thank you for thoroughly and clearly addressing my concerns about the framing of the forward tracking algorithm and of the generality of the tracking algorithms. I am also content that you have addressed most of my more minor comments from the previous manuscript, especially in avoiding over-statements and suggesting that a new physical mechanism was uncovered in the case-study.

*Minor comments:*

- L22: “memory” and “storage” could be the same thing, be clarify (perhaps RAM and non-volatile memory are meant?). Also “output-frequency sensitivity, and sampling behaviour” is vague, please be more specific.
- L60: I am not sure what is meant by “general-purpose” because it’s now clear this tracking package is really only applicable to SCALE-SDM (and perhaps limited to versions around 2.3.1(?)) and, at the moment, specific condensation and collision diagnostics. Please clarify.
- L63-74: This paragraph is repetitive with what is written in L39-44, consider restructuring to combine both paragraphs into one.
- L87: The sentence: “The framework also includes coalescence-event output and post-processing procedures for […]” is unclear because it combines two rather separate things, please reconsider what the intended message of this sentence is; “post-processing procedures” is also very vague.
- L97: please clarify what “the shared sampling and target-selection subsystem” are when first mentioned, or what they relate to (forward/backward tracking?).

Very best wishes,
Clara

Hide

RR by Anonymous Referee #2 (13 Aug 2026)

Suggestions for revision or reasons for rejection

I appreciate the substantial revision of the manuscript. The authors have addressed my previous concerns carefully. I also appreciate the development of the Two-Pass Hybrid Tracking (TPHT) workflow in response to the previous comments. Overall, I find the revised manuscript substantially improved, and my previous concerns have been adequately addressed.

I have one remaining methodological question regarding TPHT that I believe should be addressed before publication.

I note that the authors explicitly state that the two passes start from the same physical and random-number state. However, the current consistency check verifies the transfer and recovery of target IDs, but does not demonstrate that the corresponding physical histories are reproduced between the two passes. Although I recognize the authors' efforts to reproduce the identical random state, this validation is not properly discussed in the manuscript.

I would therefore ask the authors to confirm that the two passes remain physically consistent. For example, for a subset of targets, the authors could compare the timing of the first r≥15μm crossing, the radius evolution preceding that crossing, and/or the timing of the coalescence event associated with the target criterion. Such a comparison would provide a direct physical-history validation of the TPHT reconstruction in addition to the existing target-ID check.

It would also be useful to briefly discuss the numerical reproducibility requirements and limitations of TPHT. Even when the same initial state and random-number state are used, finite-precision floating-point arithmetic, differences in operation ordering, parallel execution, compiler or hardware, or changes in the sequence of random-number calls could in principle lead to divergence between stochastic realizations. Clarifying which aspects must remain identical between the two passes, and to what extent TPHT is expected to remain reproducible across different computational configurations, would help readers understand the practicality of the method.

Hide

ED: Publish subject to minor revisions (review by editor) (26 Aug 2026) by Yang Tian

AR by Chongzhi Yin on behalf of the Authors (05 Sep 2026) Author's response Author's tracked changes Manuscript

ED: Publish as is (24 Sep 2026) by Yang Tian

AR by Chongzhi Yin on behalf of the Authors (04 Oct 2026)

Short summary

We developed and tested a way to trace selected cloud particles in a simulation, including how they grow and merge. One run identifies particles that meet chosen conditions, and a second reconstructs only their saved histories. In a three-dimensional test, the saved data were estimated to be one-fifth of what would be needed to keep all particle histories. Larger reductions are possible when fewer particles are selected, making such studies more practical in large simulations.