This study attempts to understand cloud changes induced by the E3SM version change from version 1 (E3SMv1) to version 2 (E3SMv2) with comparisons between E3SM COSP simulator results and corresponding satellite data. Also, the authors try to decompose the cause of cloud change from changes in each physics scheme (MG2, CLUBB, and ZM). This paper seems to achieve the authors' goal of showing the cloud changes of the newly released version of the model and which process influences those changes. I think this paper is valuable to be published after some revisions.

Main Comment

1. For the sensitivity tests, it will be more helpful for the reader’s understanding if the authors can explain more about the parameter tuning and dCAPE_ULL trigger (object and results, briefly) even though the authors already refer to Ma et al. (2022), Golaz et al. (2022), and Qin et al. (2023).
2. I think some modifications can improve Section 4. Section 4 comprises many figures and explanations for the figures, but the objective for Section 4 does not seem clear to me. I think there might be two different ways:
   • Simplify Section 4 and concentrate more on the connection between Figures 7~11 and 12~17.
   • Describe details about how the newly adapted processes in E3SMv2 derive the differences in figures 12~17.
3. Some comments for specific sentences
   • Line 146~148: If a reference can be added, it will be helpful.
   • Line 196~197: If authors explain more about the “additional information”, it will be helpful.
   • Table 1: How about adding some information about temporal and spatial resolution, which might be different from each other?

Technical Comment

1. Both τ and Tau are used in the manuscript. It seems better to select one of them to avoid confusion.
2. Both N.H. and N. Hemisphere are used. It seems better to select one of them to avoid confusion.
3. Line 200: reginal->regional
4. Line 540: cloud fraction->CRE

Review of "Understanding changes in cloud simulations from E3SM version 1 to version 2" by Yuying Zhang et al.

[A] Overall recommendation

This study presents model simulation of cloud with two versions of a climate model, E3SM version 1 and version 2. The simulation results are evaluated against satellite observations to discuss how well the two versions can simulate the observed characteristics. The study also discusses the causes of the difference in the cloud simulations between the two versions.

The issue addressed in the paper is important. Cloud is a major factor that controls global radiative balance and hydrological cycle. However, state-of-the-art climate models still have difficulties in simulating the observed characteristics of cloud. Therefore, many of the readers of the GMD, especially those who use climate models, would be interested in the performance of the E3SM simulations. They would also be interested in how the model has improved in comparison with the previous version.

This study forwards the understanding of the issue by demonstrating that the E3SM version 2 significantly improves simulation of various cloud regimes compared to the version 1. In addition, the authors successfully indentify the causes of the improvement by isolating the roles of different parameterizations. The contents of the paper are useful to those who analyze output data from the E3SM. They are also informative to those who evaluate and improve the cloud simulations by other climate models. There are, however, some minor points to mention regarding the presentation or interpretation of the results as listed below. I would therefore recommend accepting the manuscript for publication after minor revision.

[B] Minor Comments

P.5 L.158 "considerable increase of stratocumulus cloud over the eastern ocean basins along the coasts in both hemispheres"

It would be helpful to readers if the authors specify more explicitly where they can find the increase in the stratocumulus cloud. I assume that they can find the increase along the western coasts of South Africa and North and South America, as stated in L.231.

P.9 L.258 "the CLUBB tuning has led to an increase of clouds regardless of their optical properties"

It appears to me that the CLUBB tuning has led to a decrease, not an increase, of clouds. This is because, in Figure 8(a), the "v2" run with the tuning shows less cloud compared with the "clubbonly" run without the tuning.

P.10 L.303 "indicating that the reduction of optically thin clouds shown in Figure 8 from the new trigger are mainly from low clouds"

Is there any information on middle clouds that supports this statement? I can see from Figure 12(d) that high clouds do not contribute to the reduction of optically thin clouds, but I could not find information on the middle clouds.

[C] Typos

P.1 L.11 "165-year historical simulations"

Table 2 says that they are 150-year simulations.

P.2 L.31 "re-turning"

retuning?

P.2 L.41 "To archive our goal,"

achieve?

P.4 L.116 "165-year historical simulations"

Table 2 says that they are 150-year simulations.

P.12 L.360 "Figure 12d"

Figure 11d?

P.22 L.535 "a) & d) & h) are MISR observations"

a) & d) & g)?

P.32 L.620 "optically thin cloud fraction"

optically thin low cloud fraction?

P.33 L.627 "optically intermediate cloud fraction"

optically intermediate low cloud fraction?

P.34 L.633 "optically think cloud fraction"

optically thick low cloud fraction?