General Assessment

This manuscript proposes a novel regional coupled atmosphere-ocean model (ROMSOC) that integrates COSMO and ROMS while optimizing performance on a CPU-GPU hybrid architecture. The model is applied for over Northeast Pacific with a focus on the California Current System, evaluating key air-sea interactions over a 12-year hindcast period. The manuscript also provides a detailed discussion of the potential sources of uncertainties for SST simulation bias. In general, the study presents a interesting model development work with a insightful scientific study on SST with solid method. The manuscript is well organized with detailed description of the model and thorough discussions of the result. Therefore, I would recommend it to be accepted if the following comments could be properly addressed.

Comment#1: Not really a comment but more of a curious question: the study demonstrates impressive computational efficiency with effective energy cost on a heterogeneous CPU-GPU system, but for a fixed grid configuration. How does the performance scale with different grid sizes? Similarly, as the author mentioned at line#203 it is constrained by the CPU running ROMS part, how does the performance scale with more CPU nodes? Moreover, although the practice seems very promising, is there any potential limitations, for example, is it applicable for ultra-find grid resolution like 1km?

Comment#2: The manuscript generally presents very detailed discussions regarding the potential causes for simulation bias by the coupled model, but there are limited discussions to quantify the uncertainties induced or reduced by the coupling effort. For example, SST bias of ROMSOC is primarily attributed to wind bias which indicated that the raw SST bias of ROMS is amplified by COSMO. But there is no demonstration of the 10m-wind bias by pure COSMO. I would recommend the revision to consider incorporate such kind of comparison and discussion to help better demonstrate the benefit and “side-effect” of this coupled model.

Comment#3: The study acknowledges a common bias in climate models as there are too few clouds in the southern domain over CalCS region. A more detailed discussion on why ROMSOC exhibits this behavior would be helpful to understand the limit of this specific model. This may not be directly falls into the concern of this study but: some double-momentum mechanisms have been developed for years, does COSMO support any of them, or there is any study ever try it?