Quantifying cloud adjustments and the radiative forcing due to aerosol–cloud interactions in satellite observations of warm marine clouds

Douglas, Alyson; L'Ecuyer, Tristan

doi:https://doi.org/10.5194/acp-20-6225-2020

Articles | Volume 20, issue 10

https://doi.org/10.5194/acp-20-6225-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-20-6225-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 20, issue 10

Research article

|

28 May 2020

Research article |

| 28 May 2020

Quantifying cloud adjustments and the radiative forcing due to aerosol–cloud interactions in satellite observations of warm marine clouds

Alyson Douglas and Tristan L'Ecuyer

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Final revised paper (published on 28 May 2020)
Preprint (discussion started on 23 Jan 2020)

Interactive discussion

Status: closed

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

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RC1: 'Reviewer comment', Anonymous Referee #1, 26 Jan 2020
- AC2: 'Reply to Reviewer 1', Alyson Douglas, 09 Mar 2020
RC2: 'Review of: Quantifying Cloud Adjustments and the Radiative Forcing due to Aerosol-Cloud Interactions in Satellite Observations of Warm Marine Clouds By Douglas and L’Ecuyer', Anonymous Referee #2, 13 Feb 2020
- AC1: 'Reply to Reviewer 2', Alyson Douglas, 09 Mar 2020

Peer-review completion

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

AR by Alyson Douglas on behalf of the Authors (25 Mar 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (27 Mar 2020) by Johannes Quaas

RR by Anonymous Referee #2 (31 Mar 2020)

RR by Anonymous Referee #1 (04 Apr 2020)

Suggestions for revision or reasons for rejection

The authors have done a lot to address my concerns. I have the following suggestions:

Eq. 6: I didn’t communicate this clearly in my last set of comments. When I said about accounting for 0<CF<1, what I meant was in Eq.6 you need some way of accounting for saturation in cloud fraction. When you calculate partial CF/ partial ln AI this doesn’t have any way of knowing if CF is already at 1 or 0. When adjustment forcing is calculated in Eq 6 you need some way of capping the forcing from being any more negative if CF=1 already or any more positive if CF=0, or if the projected change in CF would result in a value >1 or <0.

Conclusions: how does the interpretation of this study square with other studies looking at transient changes in aerosol that find near zero or decreased LWP with increasing Nd (Malavelle et al., 2017; Toll et al., 2019)?

Fig. 1 and 6-8: Please consider a zonal-mean plot along the side of each map plot for ease of interpretation. The colormaps are hard to read clearly. Why are some colorbars uneven (red saturates at 0.5 and blue at -3 in Fig 8, for example)? Please make colorbars symmetric about zero, or consider using something that is not diverging.

Fig. 3 Please title these plots.

Fig. 8: I still find it very odd that there is a substantial forcing from aci in the Southern Ocean. Previous studies have found almost zero PI-PD change in aerosol in this region (Hamilton et al., 2014). I acknowledge that this region might be more susceptible- and from looking at Fig. 1 ∆AI looks to be >0 so it seems that the calculation is internally consistent. However, comparison to Fig.8b of Myhre et al. (2013) shows that SPRINTARS is unique in having a nearly constant SO4 burden with latitude. The authors need to add at least one or two other aerocom models. Almost any model (HadGEM2, GISS, or ECHAM) would probably remove the band of strong ERFaci in the SH around 50S. This doesn’t really change the results of the study in the sense of the detection of a susceptibility, but is important to at least give a confidence interval on the forcing. The authors should also include a sidebar on Fig. 1a showing ∆AI as a function of latitude because it is difficult to differentiate small values in the map plot.

Hamilton, D. S., Lee, L. A., Pringle, K. J., Reddington, C. L., Spracklen, D. V., and Carslaw, K. S.: Occurrence of pristine aerosol environments on a polluted planet, Proceedings of the National Academy of Sciences, 111, 18466-18471, 10.1073/pnas.1415440111, 2014.
Malavelle, F. F., Haywood, J. M., Jones, A., Gettelman, A., Clarisse, L., Bauduin, S., Allan, R. P., Karset, I. H. H., Kristjánsson, J. E., Oreopoulos, L., Cho, N., Lee, D., Bellouin, N., Boucher, O., Grosvenor, D. P., Carslaw, K. S., Dhomse, S., Mann, G. W., Schmidt, A., Coe, H., Hartley, M. E., Dalvi, M., Hill, A. A., Johnson, B. T., Johnson, C. E., Knight, J. R., O’Connor, F. M., Partridge, D. G., Stier, P., Myhre, G., Platnick, S., Stephens, G. L., Takahashi, H., and Thordarson, T.: Strong constraints on aerosol–cloud interactions from volcanic eruptions, Nature, 546, 485-491, 10.1038/nature22974
http://www.nature.com/nature/journal/v546/n7659/abs/nature22974.html#supplementary-information, 2017.
Myhre, G., Samset, B. H., Schulz, M., Balkanski, Y., Bauer, S., Berntsen, T. K., Bian, H., Bellouin, N., Chin, M., Diehl, T., Easter, R. C., Feichter, J., Ghan, S. J., Hauglustaine, D., Iversen, T., Kinne, S., Kirkevåg, A., Lamarque, J. F., Lin, G., Liu, X., Lund, M. T., Luo, G., Ma, X., van Noije, T., Penner, J. E., Rasch, P. J., Ruiz, A., Seland, Ø., Skeie, R. B., Stier, P., Takemura, T., Tsigaridis, K., Wang, P., Wang, Z., Xu, L., Yu, H., Yu, F., Yoon, J. H., Zhang, K., Zhang, H., and Zhou, C.: Radiative forcing of the direct aerosol effect from AeroCom Phase II simulations, Atmos Chem Phys, 13, 1853-1877, 10.5194/acp-13-1853-2013, 2013.
Toll, V., Christensen, M., Quaas, J., and Bellouin, N.: Weak average liquid-cloud-water response to anthropogenic aerosols, Nature, 572, 51-55, 10.1038/s41586-019-1423-9, 2019.

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ED: Publish subject to minor revisions (review by editor) (06 Apr 2020) by Johannes Quaas

AR by Alyson Douglas on behalf of the Authors (15 Apr 2020) Author's response Manuscript

ED: Publish as is (17 Apr 2020) by Johannes Quaas

AR by Alyson Douglas on behalf of the Authors (20 Apr 2020) Manuscript

Short summary

Aerosols, or small, suspended droplets in the atmosphere, are released from anthropogenic activity and interact with warm clouds, leading to changes in the clouds' brightness and size. Our study evaluates how aerosols alter warm clouds and their ability to cool the Earth's surface. We find aerosols make clouds brighter and grow larger in the atmosphere; however, the cooling effect due to whiter, brighter clouds is 5 times the cooling due to an increased extent.