|The authors have made a substantial effort to revise the manuscript. Specifically, they have conducted three additional 5-year integrations using prescribed SST. The results of these runs provide a much more solid base comparing to those previous 1-year runs for the performance evaluation of the new model, especially in simulating atmospheric chemistry and aerosol life cycle. I also admire the authors’ effort to reemphasize their discussions on science rather than model development related topics, and also to accommodate many suggestions from the reviewers. The revised manuscript appears to be a significant improvement from the original one. In their responses and also revisions, the authors have addressed many of my concerns raised in previous review. There are, however, still a few remaining issues for the authors to improve in my opinion. The following comments are provided for the authors to consider when making their revision. |
The first issue I see a room for improvement is regarding the discussions on modeled changes of meteorological/climate variables. Specifically speaking, these include the changes of T2, Q2, WS10, precip, and PBLH. Discussions on radiative variables and cloud forcing are fine. The reason is rather simple and actually explained in my previous comment regarding the 1-year transient configuration, that is the changes of these meteorological/climate variables mostly represent exaggerated transient responses (mostly noise in other words) due to the model configuration (mainly ocean response). The adoption of climatological SST or the so-called AMIP (Atmospheric Model Intercomparison Project) configuration is an excellent choice because ocean controls to a great extent the climate responses, and observed SST largely reflects actual responses of the climate system to anthropogenic forcings. This is why such a configuration is commonly used when modeled physical or chemical features rather than dynamical feedbacks to these features are concerned. To interpret the changes of climate/meteorological variables in this configuration, however, should be constrained or simply avoided particularly when dealing with water cycle because of the stiff atmosphere-ocean interface due to prescribed SST. Again, the purpose of this paper is to demonstrate the difference in modeling chemistry and aerosol features of the new model components brought to CESM, for discussion on climate consequences, more sophisticated configuration and much longer integration time would be needed. Papers that do not follow the correct procedure might make to the “news” but would not stand long.
Several specific comments.
1. Line 23, suggest adding “thus could” before “improve model performance”; the same applies to Line 27, suggest using “could further improve” instead of “further improves”.
2. Line 32, suggest deleting “as well as near-surface … precipitation”.
3. Line 76, “…of these aerosols”, perhaps should say “of these aerosol constituents” instead.
4. Line 101-135, a very brief (1~2 sentences) summary of the major features and differences of these various schemes might be very useful.
5. Line 198-217 and other places: please make it clear enough to a wide reader group that this “J value” is referring to “nucleation rate”, not “photolysis rate”. The latter is commonly used in atmospheric chemistry literature.
6. Line 237-239, “given their…” this sentence could be revised, e.g., “giving the high computational cost due to …”.
7. Line 325-326, “All production… December 31, 2005” duplicates the previous sentence.
8. Line 387, “discussed below. That” to “discussed below, that”.
9. 4. Model Evaluation: again, here and in many other places, I’d suggest the authors to remove “meteorological” and discussions of changes of T2, Q2, and WS10 from the text and Tables. The authors could make a clear statement that the major interest of this paper is to evaluate the model performance in atmospheric chemistry and aerosol simulations.
10. Line 445: the authors might want to use a commonly used unit for OH in molecules/cm^3.
11. General comment on “5. Impacts …2001 Predictions”, perhaps more adequate terms than “2001 predictions” are “sensitivity simulations”. If prescribed 5-year SST run is computational demanding, the discussion in this section should emphasize more on the nature of these sensitivity tests exploring the differences brought by various schemes. Also, wondering if the authors want to add a few comments to compare 5.5 and later 6 (i.e., 5-year integration), because the latter demonstrates a better evaluation base for the model performance.
12. Line 945, “increases over global with a…”, indicate increases from what. There are many other similar sentences.
13. Line 950-955, again these should be avoided.
14. Line 971, “most gas species”, did the authors mean “gaseous aerosol precursors”? Line 972, “more accurate aerosol thermodynamic treatments”, is this referring to the extremely low accommodation coefficients (actually discussed a few lines later)?
15. Line 976, “previous works”, the authors might want to provide references for this, either here or in later discussion.
16. Line 979-981, “SO4= burden higher…due to greater SO2 oxidation” seems inconsistent with higher H2SO4 “due to lower mass accommodation coefficient”. Is “oxidation” here referring to aqueous phase oxidation? If so, please make it clear.
17. Line 983-984, it seems that dry deposition change is less likely to cause such a change in carbonaceous aerosol burden, also “slower … aging rate” seems inconsistent with higher H2SO4.
18, Line 1025-1040, it’s better to delete “T2”, “Q2”, “WS10”, “precip”, “meteorological” from the discussion, here and elsewhere.
19. Tables. It is odd not listing the mean values of modeled variables while listing their observed values in Table 3 – Table 7. Table 1, purpose column of MAM_NEW_5YB, “Earth’s components” reads odd.