CAM6 simulation of mean and extreme precipitation over Asia: sensitivity to upgraded physical parameterizations and higher horizontal resolution

Lin, Lei; Gettelman, Andrew; Xu, Yangyang; Wu, Chenglai; Wang, Zhili; Rosenbloom, Nan; Bates, Susan C.; Dong, Wenjie

doi:https://doi.org/10.5194/gmd-12-3773-2019

Articles | Volume 12, issue 8

https://doi.org/10.5194/gmd-12-3773-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/gmd-12-3773-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 12, issue 8

Model evaluation paper

|

28 Aug 2019

Model evaluation paper |

| 28 Aug 2019

CAM6 simulation of mean and extreme precipitation over Asia: sensitivity to upgraded physical parameterizations and higher horizontal resolution

Lei Lin, Andrew Gettelman, Yangyang Xu, Chenglai Wu, Zhili Wang, Nan Rosenbloom, Susan C. Bates, and Wenjie Dong

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Final revised paper (published on 28 Aug 2019)
Preprint (discussion started on 28 Jan 2019)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Review for: CAM6 simulation of mean and extreme precipitation over Asia: Sensitivity to upgraded physical parameterizations and higher horizontal resolution', Anonymous Referee #1, 21 Feb 2019
RC2: 'Review of: "CAM6 simulation of mean and extreme precipitation over Asia: Sensitivity to upgraded physical parameterizations and higher horizontal resolution"', Anonymous Referee #2, 21 Mar 2019
AC1: 'Final author comments', Lei Lin, 19 May 2019

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Lei Lin on behalf of the Authors (19 May 2019) Manuscript

ED: Referee Nomination & Report Request started (20 May 2019) by Paul Ullrich

RR by Anonymous Referee #1 (22 May 2019)

RR by Anonymous Referee #2 (28 May 2019)

Suggestions for revision or reasons for rejection

I thank the authors for their revisions to the manuscript. While these have largely improved the submission, unfortunately there are now some further important revisions that should be made as a result of their changes. Mainly, while the authors have followed the excellent suggestion made by Reviewer #1 to include CAM5-0.25, results from this are not shown in many of the key figures, for no apparent reason. These really should be added, and the findings discussed, particularly to support the conclusion added at the end of the Summary and the Abstract, namely that "the response to increases in horizontal resolution is dependent on CAM version."

Specific comments:

Page 4 lines 19-20: "The dataset was created by collating rain gauge measurements across Asia with gridded daily data that contains a dense network of daily rain-gauge data for Asia." ? Unclear.

Page 5 lines 18-19: As mentioned by Reviewer #1, the reader may be unclear where Sichuan province is, so please forward-reference the appropriate box in Figure 2. Further, although the purple boxes are clearly described on page 6, they should also be mentioned in the caption for Figure 2. In order to make this easier for the reader, perhaps you could consider drawing each box in a different colour on Figure 2 and then labelling them with names (rather than latitude/longitude boundaries) in the caption?

Page 6 lines 15-16: Please clarify that you are (presumably) only considering the land within these boxes. This is particularly important for the Maritime Continent region, and especially for the analysis in section 5, Table 2 and Figure 14.

Sections 3 and 4.1, 4.2, and Figures 1, 2, 4, 5, 6, 7, 8, 9 and 10: Why is CAM5-0.25 not included in these figures and this analysis? The discussion of this configuration in other sections is out of context if it is omitted here. Further, it would be very helpful to show how the influence of resolution as shown for CAM6 differs for CAM5. Please add the equivalent panels/values to these figures. For Figures 6, 7, 8 and 10 you could remove MERRA2 if you prefer a 6-panel plot. Also, to highlight the influence of the CAM5/CAM6 change and those relating to resolution, plotting differences between these (rather than differences against the benchmark) would perhaps be helpful.

Page 7 lines 13-15 and Figure 4: I still maintain that JRA55 should not be included in this Figure or this discussion of convective/large-scale partitioning - especially now that it could be replaced by results from CAM5-0.25.

Figure 5: Please add values from CPC to panel (a).

Page 9 line 3: Please add a sentence explaining to the reader what the other panels on Figure 7 show and why you added them.

Page 9 lines 9-12: Given the plethora of monsoon indices in the literature, please add an explanation as to what the DNS monsoon index is and how it is calculated.

Page 10 lines 11-12: "CAM6 improves the light rainfall over Korea, Japan and Northern China (not shown)." - it is shown; the original first part of this sentence ("The large-scale precipitation in") has been removed, so maybe you are trying to say something different with this sentence?

Page 10 lines 16-17: Isn't the first part of this (better over the Maritime Continent) also true for CAM5-0.25, but for the latter configuration the higher resolution is slightly better than the lower resolution for India, Northern and Southern China?

Figure 13: Please show and discuss results from CAM5-0.25 as well - it may reinforce your point about the influence of model physics (i.e. CLUBB), rather than resolution, in improving the diurnal cycle.

Table 2: Shouldn't the labelling of the fifth column be the same as that for the third and seventh columns?

Page 11 line 12: "less moisture" - do you mean less vertically-integrated humidity?

Page 11 line 15: Also higher resolution in CAM6/CAM5 leads to an opposite change in total cloud amount over Southwestern China.

Page 11 line 19: The lack of increase in PRECC despite increased FSDS and LHFLX may be related to the decrease in INT_Q?

Page 12 line 5: Isn't the largest difference (relative to JRA55) in the budget for southwestern China in the zonal moisture flux convergence term?

Page 12 line 11: Remove "in CAM6" from this sentence.

Page 12 lines 11-17: Please clarify the similarities and differences between the resolution impacts in CAM5 and CAM6, e.g. they have opposite changes in total cloud (presumably related to the larger increase in FSDS and LHFLX in CAM5?) and in downwelling clear-sky solar flux.

Page 12 lines 19-20: Isn't it the zonal term that dominates?

Page 12 and Figure 14: I still feel dissatisfied with this section. The moisture budget analysis is not comprehensive for any of the regions, and particularly now that the Maritime Continent region has been included. There is ample literature suggesting that many GCMs show sensitivity to resolution over this region, relating to the representation of topography and coastlines of the islands. Johnson et al. (2016) carried out moisture budget analysis for the Maritime Continent region as a whole (including the ocean) that suggested the increased resolution altered the budget and the rainfall between the southern (windward) and northern (leeward) parts of the region. While you may not wish to go into great detail for this particular region in this study, a little more discussion of the moisture budget regarding the changes with model physics and resolution, and reference to existing literature, would be helpful.

Page 13 Summary: Other than a final sentence stating that the influence of resolution depends on the CAM model version, this section largely fails to draw out the details of this dependence (largely because CAM5-0.25 is omitted from many of the Figures). Clarifying this dependence would set a better context for the results from CAM6.

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ED: Reconsider after major revisions (07 Jun 2019) by Paul Ullrich

AR by Lei Lin on behalf of the Authors (26 Jun 2019) Author's response Manuscript

ED: Publish as is (11 Jul 2019) by Paul Ullrich

AR by Lei Lin on behalf of the Authors (12 Jul 2019) Manuscript

Short summary

Here we evaluate the performance of the Community Atmosphere Model version 6 (CAM6) released in 2018, with the default 1º horizontal resolution and a higher-resolution simulation (approximately 0.25º), against various precipitation observational datasets over Asia. With the prognostic treatment of precipitation processes (which is missing in CAM5) and the new microphysics module, CAM6 is able to better simulate climatological mean and extreme precipitation over Asia.