Impacts of cloud microphysics parameterizations on simulated aerosol–cloud interactions for deep convective clouds over Houston

Zhang, Yuwei; Fan, Jiwen; Li, Zhanqing; Rosenfeld, Daniel

doi:https://doi.org/10.5194/acp-21-2363-2021

Articles | Volume 21, issue 4

https://doi.org/10.5194/acp-21-2363-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-21-2363-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 21, issue 4

Research article

|

18 Feb 2021

Research article |

| 18 Feb 2021

Impacts of cloud microphysics parameterizations on simulated aerosol–cloud interactions for deep convective clouds over Houston

Yuwei Zhang, Jiwen Fan, Zhanqing Li, and Daniel Rosenfeld

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Final revised paper (published on 18 Feb 2021)
Supplement to the final revised paper
Preprint (discussion started on 06 May 2020)

Interactive discussion

Status: closed

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

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RC1: 'Review of “Impact of cloud microphysics parameterizations of simulated aerosol-cloud-interactions for deep convective clouds over Houston” by Zhang, Fan, Li and Rosenfeld', Anonymous Referee #1, 05 Jun 2020
- AC3: 'Withdraw the file "Response to RC1"', Yuwei Zhang, 14 Aug 2020
RC2: 'Review of “Impacts of Cloud Microphysics Parameterizations on Simulated Aerosol-Cloud Interactions for Deep Convective Clouds over Houston” by Zhang et al.', Anonymous Referee #2, 09 Jun 2020
- AC4: 'Withdraw the file "Response to RC2"', Yuwei Zhang, 14 Aug 2020
AC1: 'Response to RC1', Yuwei Zhang, 14 Aug 2020
AC2: 'Response to RC2', Yuwei Zhang, 14 Aug 2020
- RC3: 'reply to the authors' response to referee 2 comments', Anonymous Referee #2, 25 Aug 2020
  - AC7: 'Response to RC3', Yuwei Zhang, 05 Sep 2020
AC5: 'Response to RC1 - correct version', Yuwei Zhang, 03 Sep 2020
AC6: 'Response to RC2 - correct version', Yuwei Zhang, 03 Sep 2020

Peer-review completion

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

AR by Yuwei Zhang on behalf of the Authors (03 Sep 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (08 Sep 2020) by Fangqun Yu

RR by Anonymous Referee #2 (16 Sep 2020)

Suggestions for revision or reasons for rejection

Review of the revised manuscript “Impacts of Cloud Microphysics Parameterizations on Simulated Aerosol-Cloud Interactions for Deep Convective Clouds over Houston” by Zhang, Fan, Li, and Rosenfeld, considered for publication in ACP, manuscript acp-2020-372.

Recommendation: additional revisions needed

The revised manuscript has been improved. In particular, the invigoration (that is really only tangentially related to this study) is now better presented as still a controversial subject requiring additional studies. First, let me note that not all of my points have been addressed. In particular, I suggested that the two schemes applied in the simulations, and specifically their ice components, need to be explained in more detail (see my previous point 7). The additional material added in the revision provides some confusion to me, see below. I would either expand the analysis or remove part of that material to create no confusion, see specific comments below. This material is really not needed for the main thrust of the paper, and it should be suitable for a future manuscript when more analysis is done. Perhaps the most significant comment at this stage is that in my opinion the authors provide a bias interpretation of some of the figures. I present specific examples below. Also, some figures require adjustments as detailed below.

I should also mention in passing, that I am not fully satisfied with our previous exchanges, the quasi-equilibrium supersaturation discussion in particular. However, since this aspect is not part of the manuscript, I will put this issue aside, perhaps with the exception of the comment 2 below.

Specific comments:

1. The first sentence of section 2 is a repetition of the text a couple lines above, at the end of section 1. Please remove either one.

2. L. 228-229: What do you mean: “…the supersaturation for condensation and evaporation are calculated after the advection”? Do I understand that the model advects temperature and water vapor, and then combined the two to create supersaturation that is subsequently applied in microphysical calculations? If so, this is simply wrong as supersaturation calculated this way has no physical meaning and it depends on the time step applied in the advection (the longer the time step the larger the supersaturation calculated this way). If this is how WRF model works, this is a shame. There are different methods to do this correctly. See, for instance, the seminal paper by Hall (JAS 1980, p. 2486; see discussion in section 3e). My suggestion is to remove this sentence and not to open the Pandora box. But this is something to think about for the future.

3. Figure 3: as in my previous comments, there are more points with different colors than in agreement with the model. The phrase “though not exactly the same” in l. 258 in a stretch. My suggestion is to remove this figure and only include Fig. 4, maybe with the time averages. But if the goal is to show the spatial pattern, then please say that the model represents the spatial pattern, but has problems with specific measurement sites, not surprisingly I would think.

4. Figure 4. The comparison between model and satellite estimates is difficult. Maybe scatterplots (i.e., one versus the other, without geographic information) would be better?

5. Figure 6. Models are close to each other and they both miss to represent E-W temperature gradient apparent in the observations. Why?

6. Figure 7 is really nice, but its discussion in the text is not. First, it is great to see that all model realizations feature a cluster of convective cells in the red box (as in observations), and some convection NE to the red box. Is the position of the cluster inside the red box related to the aerosol gradient between the Houston and its vicinity? I am also not sure if I see the differences the text emphasizes. To me, model results are simply slightly different realizations of the same convective situations. If anything, the SBM realizations look a little more “diffused” to me.

7. Figure 9 and its discussion. First, I prefer to consider rain accumulation, not intensity, as more instructive. The upper panel has to include line definitions. Models start earlier than observations, solid lines before dashed (I do not know which one is which). To me, all lines are simply different realizations. Bottom panel: the anth and noanth reverses in both schemes between small rates (noanth larger) and high rates (anth larger). This should be mentioned. I suggest to use linear scale (different for different rate ranges) as the linear scale shows much better the difference. The way the figure is plotted now (rate rather than accumulation in the upper panel and log scale in the lower panel) is suboptimal. The text emphasizes differences (“remarkable” in l. 321) that I do not see. The same for the difference between SBM and MOR: the lower panel shows similar trend and I do not see what the text says in lines 321-325.

8. Figure 10. The impact of pollution is remarkably similar in both models. I do not see much invigoration below freezing levels (that may come from different supersaturation treatment in SBM and MOR) and there is some aloft. But where it does come from for MOR? Maybe because of difference in ice processes? But we do not know how ice processes differ in the two models. This comment is also important to understand the impact of supersaturation prediction in MOR simulations.

9. Figure11. Left and right panels (SBM and MOR) are remarkably similar. NB, I commented before that the term “thermal buoyancy” has to be replaced by “buoyancy”; “thermal” is confusing because buoyancy has to include temperature and all water variables. The difference between MOR_noanth and MOR_anth has to do with different flow realizations, at least below the freezing level (again, what about ice representation?). There is no other explanation unless one argues about the feedback from rain processes. The MOR_SS results are unexpected as it shows the opposite impact of including finite supersaturation on the mean updraft, buoyancy, and latent heating. The rest of the manuscript tries to explain this surprising result.

10. To understand the effects of supersaturation prediction in MOR_SS simulations, one needs to know more details on how the prediction is linked to the microphysics. For instance, how does the change affect the droplet activation and ice processes? Grabowski and Morrison (JAS 2017, p. 2247) document some impacts on ice processes when saturation adjustment is replaced with saturation prediction. Do you still use Ghan et al. droplet activation parameterization when predicting supersaturation? How ice initiation is affected? Fig. 13 shows that saturation prediction has small impact on droplet activation (mass-wise), but large and unexpected impact on the condensation rate. How is the latter possible? I think an attempt is made to explain this in the rest of the paper, but I suggest to remove that part and MOR_SS simulations altogether as only tangentially related to main results of this study.

11. Figure 13: what is “condensation rate” in lower panels? Is that water vapor to cloud water, or water vapor to either water or ice? Please clarify.

12. I have to admit that I did not read and study figures beyond 13, but I find similarities between simulations applying the SBS and MOR schemes remarkable. This should be emphasized in the paper.

13. In view of my comments above, I do not agree with many statements in the concluding section 5, especially those related to cold and warm invigoration. I feel the section does not properly reflect results presented in the figures and is biased towards the authors’ view rather than what model results show. This has to change before the manuscript is accepted.

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RR by Anonymous Referee #1 (22 Sep 2020)

Suggestions for revision or reasons for rejection

Rerview of manuscript “Impact of cloud microphysics parameterizations of simulated aerosol-cloud-interactions for deep convective clouds over Houston” by Zhang, Fan, Li and Rosenfeld. -revised manuscript

I appreciate the authors’ effort of adding Figs. 16 - 18, comparing the original Morrison scheme with modified Morrison scheme (MOR_SS). The conclusion, that enhanced ice processes similar to the “cold-phase invigoration” are responsible for enhanced invigoration simulated in MOR_SS, is plausible. With these new analysis, the authors then added several lines to the end of the original abstract, which unfortunately made its logic confusing. The abstract reads: “With the SBM scheme, we see a significant invigoration effect on convective intensity and precipitation by anthropogenic aerosols mainly through enhanced condensation latent heating (i.e., the warm-phase invigoration). Whereas such an effect is absent with the Morrison two-moment bulk microphysics, mainly because the saturation adjustment approach for droplet condensation and evaporation calculation removes the dependence of condensation on droplet properties and limits the ice processes by a more efficient conversion of droplets into raindrops, which leads to less cloud droplets being transported to the altitudes above the freezing level.” My interpretation of this passage is: SBM scheme simulated significant invigoration. The mechanism is mainly through enhanced condensation (enhanced warm-phase invigoration). Morrison scheme produced less invigoration. The reason is related to reduced ice processes (reduced cold-phase invigoration?). To paraphrase based on Figs. 16 - 18, the MOR_SS scheme produced significant invigoration due to enhanced ice processes? Here both SBM and MOR_SS are compared to the original Morrison scheme. But SBM have more invigoration due to warm-phase processes. And MOR_SS, with similar invigoration as SBM, is due to cold-phase invigoration? How can this inference be? Shouldn’t the invigoration mechanism be the same for both the SBM and the MOR_SS?

I maintain that the manuscript tackles an important, and difficult problem. It has solid and comprehensive analysis and qualifies for ACP publication. Revisions are needed in the abstract and conclusions, especially the abstract, to avoid ambiguity and keep focus. I recommend publication after minor revision.

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ED: Reconsider after major revisions (24 Sep 2020) by Fangqun Yu

AR by Yuwei Zhang on behalf of the Authors (03 Nov 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (09 Nov 2020) by Fangqun Yu

RR by Anonymous Referee #2 (01 Dec 2020)

ED: Publish subject to minor revisions (review by editor) (03 Dec 2020) by Fangqun Yu

AR by Yuwei Zhang on behalf of the Authors (11 Dec 2020) Author's response Manuscript

ED: Publish as is (14 Dec 2020) by Fangqun Yu

AR by Yuwei Zhang on behalf of the Authors (18 Dec 2020)

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Short summary

Impacts of anthropogenic aerosols on deep convective clouds (DCCs) and precipitation are examined using both the Morrison bulk and spectral bin microphysics (SBM) schemes. With the SBM scheme, anthropogenic aerosols notably invigorate convective intensity and precipitation, causing better agreement between the simulated DCCs and observations; this effect is absent with the Morrison scheme, mainly due to limitations of the saturation adjustment approach for droplet condensation and evaporation.