Is a more physical representation of aerosol activation needed for simulations of fog?

Poku, Craig; Ross, Andrew N.; Hill, Adrian A.; Blyth, Alan M.; Shipway, Ben

doi:https://doi.org/10.5194/acp-21-7271-2021

Articles | Volume 21, issue 9

https://doi.org/10.5194/acp-21-7271-2021

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

https://doi.org/10.5194/acp-21-7271-2021

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

Articles | Volume 21, issue 9

Research article

|

12 May 2021

Research article |

| 12 May 2021

Is a more physical representation of aerosol activation needed for simulations of fog?

Craig Poku, Andrew N. Ross, Adrian A. Hill, Alan M. Blyth, and Ben Shipway

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Final revised paper (published on 12 May 2021)
Preprint (discussion started on 07 Sep 2020)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Referee comment', Anonymous Referee #1, 04 Oct 2020
- AC1: 'Reply on RC1', Craig Poku, 18 Mar 2021
RC2: 'Review of ACP-2020-904 : « Is a more physical representation of aerosol activation needed for simulations of fog?” by Craig Poku et al.', Anonymous Referee #2, 27 Oct 2020
- AC2: 'Reply on RC2', Craig Poku, 18 Mar 2021

Peer-review completion

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

AR by Craig Poku on behalf of the Authors (18 Mar 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (19 Mar 2021) by Johannes Quaas

RR by Anonymous Referee #2 (06 Apr 2021)

Suggestions for revision or reasons for rejection

Based on reviewer comments, the paper has been significantly improved by providing a more detailed comparison with IOP1 observations and expanded the discussion to account for highlighted discrepancies in the work.
However a few last concerns already raised need to be better introduced before acceptation and I insist on it.

My concerns are that:

- Concerning the initialization of aerosol I still do not agree that a single accumulation mode with 100 cm-3 is representative of typical measurements for a clean rural site similar to Cardington. In Boutle et al. (2018), it is clearly said that aerosol distribution representative of the clean air typically found at Cardington is 1000 cm-3 concentration of Aitken-mode aerosols, 100 cm-3 accumulation-mode aerosols and 2 cm-3 coarse-mode aerosols. I understand that you have not the possibility for the moment to use a multi-mode aerosol spectrum which is perfectly admissible. But I am not at all convinced that considering 100 cm-3 accumulation-mode aerosols is equivalent as you rely on tests not shown. Therefore you have to say that: i) an aerosol distribution of 1000 cm-3 concentration of Aitken-mode aerosols, 100 cm-3 accumulation-mode aerosols and 2 cm-3 coarse-mode aerosols as proposed and used in Boutle et al. (2018) would be better representative of the clean air typically found at Cardington but cannot be used in this paper; ii) the assumption of a single accumulation mode with 100 cm-3 probably limits the overestimation of droplet concentration that would lead to a too rapid transition to a thick fog layer.

- You have not answered to my previous question:
For the visibility calculation, why not to use a direct calculation according to the Koschmieder (1925) equation, linking the visibility to an extinction coefficient function of the DSD, through the Mie theory, instead of a diagnostic from Gultepe et al. (2006), which could be questionable ?

- Line 470: The reference Thouron et al. (2012) for stratocumulus needs to be cited for the prognostic supersaturation in the same way as Lebo et al. (2012) for deep convective clouds.

Reference :

- Thouron, O., J.-L. Brenguier, and F. Burnet, Supersaturation calculation in large eddy simulation models for prediction of the droplet number concentration, Geosci. Model Dev., 5, 761-772, 2012.

Referee Report: PDF

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ED: Publish subject to minor revisions (review by editor) (07 Apr 2021) by Johannes Quaas

AR by Craig Poku on behalf of the Authors (08 Apr 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (08 Apr 2021) by Johannes Quaas

AR by Craig Poku on behalf of the Authors (08 Apr 2021)

Short summary

We present a new aerosol activation scheme suitable for modelling both fog and convective clouds. Most current activation schemes are designed for convective clouds, and we demonstrate that using them to model fog can negatively impact its life cycle. Our scheme has been used to model an observed fog case in the UK, where we demonstrate that a more physically based representation of aerosol activation is required to capture the transition to a deeper layer – more in line with observations.