Dear Author

Thank you for this revised version of your manuscript. I think it has considerably improved compared to the first version but there are still many important points that need clarification. In particular, I consider that in many cases, you don’t reply to the reviewer’s comments in a satisfactory way. Therefore I suggest you analyse and reply to my following comments before the manuscript can be considered for publication.

With best regards,
Sophie Valcke

Dear Author,

Thank you for this revised version of your manuscript that addresses most of the remarks I made in my first round of reviews. However, I have still few important remarks that I would like you to take into account before publishing the manuscript in GMD. Please find here below these remarks and finally a list of suggestion for improving the English writing.

1- Remaining remarks

• P.2, L.14-16: In “Considering this, and that the next C-Coupler versions may not be compatible with C-Coupler1, we did not aim to achieve wide usage of C-Coupler1, but sought to overcome the limitations while guaranteeing backwards compatibility in subsequent C-Coupler versions”, the first part of the sentence “the next C-Coupler versions may not be compatible with C-Coupler1” seems contradictory to the last part of the sentence “while guaranteeing backwards compatibility in subsequent C-Coupler versions”. Please modify and clarify.

• P.6, L.7-8: you should not write “Most existing couplers require the user to develop explicitly all coupling procedures”; some do but I would not write that most of them do.

• If I understand well, the software structure illustrated on Figure 1 was never implemented as such. C-Coupler1 and C-Coupler-2 structures are illustrated on Figure 2 and Figure 4 respectively. Therefore, what is represented on Figure 1 should be referred in the caption and in the text to as “General software design of C-Coupler” (i.e. with “design” instead of “structure”). Please change Figure 1 captions and the text referring to Figure 1 accordingly. For example, I think that writing on P.9, L.2-3 “This software structure is similar to that of the original C-Coupler software design (Fig. 1)” and on P.9, L.4 “The original design of the C-Coupler …” would be clearer.

• P.17, L.21: after “… has experienced two designs”, please add (as explained in your reply) “The second design can be viewed as an upgrade of the first design and is currently implemented in C-Coupler2”.

• P.19, L.1: This whole section 4.1.1.9 is too detailed and related Figures 6 and 7 are too hard to read. I suggest moving them to a supplement and referencing to the supplement at the beginning of section 4.1.1.

• P.24, L.8: please add “The choice is done by the user when registering the import interface” there as the explanation on P.25, L.24-26 is too far below.

• P.24, L.15: for clarity, please add “based on the user’s choice”.

• Section 4.3, P.22-26: should be subdivided into subsections for better readability, I suggest:
o “4.3.1 Creation of MPI communicators” : from P.22,L.28 to P.23,L.28
o “4.3.2 Timers matching and lags”: from P.23,L.29 to P.24,L.32
o “4.3.3 Steps for coupling procedure generation”: from P.24,L.33 to P.26, L.2

• P.27, L.22-30: I am not sure why this paragraph is written putting emphasis on OASIS3-MCT and not on C-Coupler2. The current paper is on C-Coupler2 and not on OASIS3-MCT so this should be modified. Describe how non-blocking data transfer is implemented in C-Coupler2 and then maybe conclude “Similar non-blocking data transfer is implemented in OASIS3-MCT”. Also sentence starting with “To achieve non-blocking data transfer …” and ending with “… last put of the same coupling field” is way to cumbersome; please rephrase and simplify.

• P.28, L.17-19: You write “if all model time tags in its message passing buffer … are the same and later than the tags of the last receive, it means that new coupling field values have been received”; I don’t understand how a new coupling field can be associated with same tags than the last receive; I would say that a new coupling field is only associated with tags later than the tag of the last receive. Please clarify or correct if I am right.

• P.29,L.6: I still don’t understand, as in my first round of review, what do you mean by “it is unnecessary to execute imp2_1”; I have the same question with imp2_1 and imp2_2 on Fig 9(c). The component model needs those input fields to run, where will it get it from ???

• P.30,L.1: change “unbreakable” for “unsolvable”; I understand that 9(e) case is unsolvable even with one-sided MPI communication where message passing buffers can be increased adaptively; if I am right, please state it in the text by adding “(even with one-sided MPI communication)” after “deadlock”.

• P.30,L31-32: how do you define “coupling latencies”?

• Section “4.8 Adaptive restart capability”: I consider that this section is still too complex and very hard to follow and understand. I propose to move this whole section and Figure 10 to a supplement and to provide in the paper just a summary of the C-Coupler2 adaptive restart capability. (Note that on p.34, “bybrid” should be “hybrid”).

• Section 4.9 is too detailed for a paper; this section looks more like a section of the User Guide. In my comment from the previous round of review, I did not ask for a whole new section on defaults, I just asked to mention somewhere that default for each option is described in the User Guide. Please remove section 4.9 and just add somewhere in the text that default for each option is described in the User Guide.

• P.40, L.1: how can you speculate about the C-Coupler2 memory usage based on the assessment of OASIS3-MCT? This seems quite unjustified to me. Please clarify or modify.

• Section “6 Future work”: this section was improved compared to the previous version but I think it is still too weak. I think you should turn this section into “Summary and future work” including a first half page summarizing the differences between C-Coupler1 and C-Coupler2, i.e. highlighting the most important points from Table 2 and then going on with what you currently have in your section “6 Future work” with one paragraph on the integration of external calculation routines (current P.41, L.1-9), one paragraph on the coupling configuration interface backward compatibility (current P.41, L.10-11) and one paragraph on initialization cost and memory use (current P.41, L.12-14)


2- Suggestion for English improvement

• P.1, L15-16: consider changing “and automatic coupling procedure generation that enables to automatically generate coupling procedures for any subset of component models” for “and automatic coupling procedure generation for any subset of component models”

• P.1, L.19-20: consider changing “It has passed a number of test cases derived from a sample model with model coupling and nesting,” for “It has passed a number of test cases involving model coupling and nesting,”

• P.1, L.28: remove “new” in “new features” (as they are not new anymore!)

• P.1, L.28-29: I still think that “There are two coupled models with C-Coupler1” is not nicely phrased. As suggested in my previous minor comment, please consider changing this sentence for “Two coupled models were built using C-Coupler1”.

• P.3, L.7, change “coupled model coupled by any coupler” for “coupled model using any coupler”

• P.3, L30, change “without a coupler component” for “without a separate coupler component”

• P.6, L.18: As the sentence starts with “In a two-way coupled model”, the last part of the sentence “(i.e., two-way coupled)” is useless; please remove it.

• P.6, L.21: I think that “we recommend” would be better than “we advice”.

• P.8, L.19: I think that “where they run exits” should be changed for “when their run exits”

• P.9, L.15-17: instead of writing “manager” 10 times, you should write “… of C-Coupler2 include managers for non-blocking data transfer, component model, grid, …”

• P.22, L.16: remove “to support coupling within one executable or a subset of MPI processes” as this is totally redundant with the rest of the sentence.

• P.23, L.29: make the sentence lighter by removing “that couples a subset of fields”

• P.24, L.9: using the word “swapping” is confusing. I think the sentence would be better stated as: “As an additional example, suppose that periods of the import and export timers are now 200 and 900 s, respectively, still …”

• P.24, L.27: use of “require” is inappropriate here as it is not the target model that decides from where will come his input fields; I suggest changing “require” for “receive”.

• Section 4.4 and in section 5.5: SIGMA and HYBRID do not need to be in capital letters; please change “SIGMA” for “sigma” and “HYBRID” for “hybrid”.

• P.26, L.29: change “achieve” for “complement”

• P.28, L.23: remove “of executing import interfaces”

• P.29, L.19-20: change “unbreakable” for “unsolvable”

• P.29, L.30: use of “wants” is inappropriate here as it is not the target model that decides from where will come his input fields; I suggest changing “wants” for “will receive”.

• P.40, L.29: put “design” instead of “designs”

Dear Author,

Thank you for these revisions that make the manuscript suitable for publication. I have however the following technical corrections that you could consider for the final version of the manuscript:
• P.27, L.2: add “for” before “achieving”
• P.27, L.5-8: this sentence is still too cumbersome. Please rephrase as: “To achieve non-blocking data transfer based on two-sided MPI communication, the import interfaces of C-Coupler2 are blocking while the export interfaces use the non-blocking mode; a mechanism that afterwards checks and waits for the completion of the last execution of export interfaces is used.”
• P.31, section 4.8: I am sorry to say that I still can’t follow that section but I am not sure what can be done about this; we can keep this section as is and hopefully it will be useful for some users.
• I don’t see anywhere in the text the mention that defaults for the different options are provided in the User Guide, maybe this mention could be added.
• P.36, L.13: Maybe change “remained” for “remains”
• P.37, L.27: The word “couple” is used in 4 out of 8 words! Maybe rephrase as “… does not support coupled component models using other couplers.”
• P.38, L10: Change “For example,…” for “Therefore,…”

With best regards