Regarding model convergence with increased/decreased layers:

While our current study focuses on comparing two vertical coordinate systems (HYBRID and ZSTAR) under identical vertical degrees of freedom (75 layers), we agree that assessing model convergence by systematically increasing or decreasing the number of layers (e.g., 37-layer or 150-layer configurations) would provide additional insight. However, such convergence experiments were not included in this manuscript primarily due to computational cost and because our primary objective was to evaluate the sensitivity of ocean circulation and hydrography to the choice of vertical coordinate system. We acknowledge the importance of convergence testing and plan to address this aspect in future work.

Regarding optimization of the hybrid vertical coordinate for the regional domain:

We appreciate your insightful comments regarding the applicability of the hybrid vertical coordinate system and the potential for further optimization of the target density layers for our regional model configuration.

As noted, the current hybrid coordinate configuration employed in this study was adapted from a previously published global MOM6 setup. This choice was initially made to maintain consistency and comparability with established global modeling practices. However, we fully acknowledge that the range of density classes relevant to our Northwest Pacific regional domain is more restricted, and thus the default global configuration may not be optimal across all subregions.

To address this concern, we have conducted additional sensitivity experiments using modified sets of target densities in the hybrid coordinate. These experiments indicate that the target density range adopted from the global setup performs reasonably well in capturing key water mass structures in the Northwest Pacific. In particular, it effectively represents the Kuroshio and the North Pacific Intermediate Water, both in terms of core depth and vertical extent. These findings support the suitability of this target density configuration for representing the large-scale features within our domain.

Nonetheless, the results presented in the current manuscript also reveal regional limitations, especially in high-latitude marginal seas such as the East/Japan Sea and the Sea of Okhotsk. In these regions, where stratification is relatively weak, the fixed target density distribution results in a substantial loss of vertical resolution in the upper water column. This resolution loss likely contributes to the degraded performance in representing summer stratification and internal tide dynamics in these areas. We agree that a more regionally optimized hybrid coordinate—potentially with an adjusted density range could alleviate these deficiencies.

We are currently designing a follow-up experiment that incorporates a modified hybrid coordinate tailored to improve vertical resolution in weakly stratified environments. While such results are not yet available for inclusion in the present manuscript, we plan to report them in a future study. We will revise the discussion section to include this point as a future direction for improving the performance of hybrid coordinate systems in marginal seas.

Once again, we thank you for this valuable suggestion.

Dear Reviewer,

We sincerely appreciate your thoughtful and constructive comments.

Please find attached our detailed responses to your remarks.

Kind regards,

Inseong Chang and Young Ho Kim

Dear Reviewer,

We are grateful for your careful review and valuable suggestions.

Enclosed please find our detailed replies to your comments.

Sincerely,

Young Ho Kim

Dear Reviewer,

Thank you for your helpful comments.

Please find our responses attached for your review.

Sincerely,

Young Ho Kim