Aerosol influences on low-level clouds in the West African monsoon

Taylor, Jonathan W.; Haslett, Sophie L.; Bower, Keith; Flynn, Michael; Crawford, Ian; Dorsey, James; Choularton, Tom; Connolly, Paul J.; Hahn, Valerian; Voigt, Christiane; Sauer, Daniel; Dupuy, Régis; Brito, Joel; Schwarzenboeck, Alfons; Bourriane, Thierry; Denjean, Cyrielle; Rosenberg, Phil; Flamant, Cyrille; Lee, James D.; Vaughan, Adam R.; Hill, Peter G.; Brooks, Barbara; Catoire, Valéry; Knippertz, Peter; Coe, Hugh

doi:https://doi.org/10.5194/acp-19-8503-2019

Articles | Volume 19, issue 13

https://doi.org/10.5194/acp-19-8503-2019

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

Special issue:

Results of the project "Dynamics–aerosol–chemistry–cloud...

https://doi.org/10.5194/acp-19-8503-2019

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

Articles | Volume 19, issue 13

Research article

|

04 Jul 2019

Research article |

| 04 Jul 2019

Aerosol influences on low-level clouds in the West African monsoon

Jonathan W. Taylor, Sophie L. Haslett, Keith Bower, Michael Flynn, Ian Crawford, James Dorsey, Tom Choularton, Paul J. Connolly, Valerian Hahn, Christiane Voigt, Daniel Sauer, Régis Dupuy, Joel Brito, Alfons Schwarzenboeck, Thierry Bourriane, Cyrielle Denjean, Phil Rosenberg, Cyrille Flamant, James D. Lee, Adam R. Vaughan, Peter G. Hill, Barbara Brooks, Valéry Catoire, Peter Knippertz, and Hugh Coe

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Final revised paper (published on 04 Jul 2019)
Preprint (discussion started on 21 Jan 2019)

Interactive discussion

Status: closed

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

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RC1: 'Review of: Aerosol influences on low-level clouds in the West African monsoon, 2019', Anonymous Referee #1, 11 Feb 2019
RC2: 'Review of "Aerosol influences on low-level clouds in the West African monsoon" by Jonathan W. Taylor et al.', Anonymous Referee #2, 22 Feb 2019
RC3: 'Review', Anonymous Referee #3, 27 Feb 2019
AC1: 'Responses to reviewers' comments', Jonathan Taylor, 30 Apr 2019

Peer-review completion

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

AR by Jonathan Taylor on behalf of the Authors (30 Apr 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (08 May 2019) by Lynn M. Russell

RR by Anonymous Referee #1 (13 May 2019)

Suggestions for revision or reasons for rejection

The authors have thoroughly adjusted the manuscript based on the comments of the three reviewers. I believe most of the changes and responses are satisfactory and the manuscript is improved. I would like to suggest one minor revision to the wording of one of their main points. If my understanding is correct, the authors assume that the onshore particles greater than 250 nm is equal to the particles offshore + particles with onshore sources. For example, if offshore >250 nm concentrations were observed to be 100 cm^-3 and on shore was observed to be 150 cm^-3 the assumption the authors use indicates that 100 of the 150 particles on shore are from long range transport offshore.
I am not so sure I can agree with this assumption. At least not without some sort of tracer to identify if the transported air mass has become diluted. The authors do use CO as an indicator of offshore long range transport of biomass burning, however CO onshore would also be influenced by local sources making it difficult to identify the contribution of offshore particles to onshore concentrations. Even if one were to assume the on shore sources of CO had little effect on most of the measurements (probably a bad assumption), an onshore CO concentration lower than the offshore CO concentration would indicate dilution of the airmass and suggest fewer particles are from long range transport. I am not sure how much, but I would expect there to be some dilution of particles coming onshore.
I suggest a more general statement like: onshore accumulation mode particles are only 40% higher than offshore concentrations (rather than assuming most onshore particles originated from offshore as you have stated: "aerosol imported from offshore comprised the majority of accumulation mode aerosol inland" ). This difference in accumulation mode particles, along with differences in dynamics, accounts for the mildly higher (~50%) CDNC onshore.

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RR by Anonymous Referee #3 (03 Jun 2019)

ED: Publish subject to minor revisions (review by editor) (03 Jun 2019) by Lynn M. Russell

AR by Jonathan Taylor on behalf of the Authors (03 Jun 2019) Author's response Manuscript

ED: Publish as is (04 Jun 2019) by Lynn M. Russell

AR by Jonathan Taylor on behalf of the Authors (10 Jun 2019) Manuscript

Short summary

Low-level clouds cover a wide area of southern West Africa (SWA) and play an important role in the region's climate, reflecting sunlight away from the surface. We performed aircraft measurements of aerosols and clouds over SWA during the 2016 summer monsoon and found pollution, and polluted clouds, across the whole region. Smoke from biomass burning in Central Africa is transported to West Africa, causing a polluted background which limits the effect of local pollution on cloud properties.