Aerosol–fog interaction and the transition to well-mixed radiation fog

Boutle, Ian; Price, Jeremy; Kudzotsa, Innocent; Kokkola, Harri; Romakkaniemi, Sami

doi:https://doi.org/10.5194/acp-18-7827-2018

Articles | Volume 18, issue 11

https://doi.org/10.5194/acp-18-7827-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-18-7827-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 18, issue 11

Research article

|

04 Jun 2018

Research article |

| 04 Jun 2018

Aerosol–fog interaction and the transition to well-mixed radiation fog

Ian Boutle, Jeremy Price, Innocent Kudzotsa, Harri Kokkola, and Sami Romakkaniemi

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Final revised paper (published on 04 Jun 2018)
Preprint (discussion started on 13 Oct 2017)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'accept with major improvement', Anonymous Referee #1, 24 Oct 2017
- AC1: 'Response to reviewer 1', Ian Boutle, 14 Nov 2017
  - RC3: 'discussion about this reply', Anonymous Referee #1, 21 Nov 2017
    - AC2: '2nd response to reviewer 1', Ian Boutle, 29 Jan 2018
RC2: 'Review', Anonymous Referee #2, 26 Oct 2017
- AC3: 'Response to reviewer 2', Ian Boutle, 29 Jan 2018

Peer-review completion

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

AR by Ian Boutle on behalf of the Authors (29 Jan 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (18 Mar 2018) by Yafang Cheng

RR by Anonymous Referee #2 (28 Mar 2018)

RR by Anonymous Referee #1 (29 Mar 2018)

Suggestions for revision or reasons for rejection

The meticulous corrections of the authors have resulted in a manuscript that is greatly improved.
Yet I am left with an uncomfortable feeling about this paper.
This work demonstrates that modifications in the droplet number could have a significant effect during the formation of fog.
However the authors do not discuss in depth the physical mechanisms responsible of this sensitivity.
As said in conclusions, it seems that this sensitivity only appears for low values of drop numbers : Maronga and Bosveld (2017) and Steeneveld and Bode (2018) have found no sensitivity for values between 100 a 300 cm-3, and the authors found a strong sensitivity for values between 75 and 50 cm-3.
This threshold sensitivity should be explained in details before the manuscript could be accepted for publication in ACP.

-The first concern is the fact that the authors have omitted a thorough discussion of the microphysical processes related to the droplet number modification.
What is the main impact of the modification of the fog droplets number on microphysical processes?
effect on sedimentation? radiative effect? Why?
Please quantify the effect of the microphysical modifications. Comparison with observation made during LANFEX (e.g. validation of the sedimentation with the measasured surface water deposition) could be helpful to better understand the threshold sensitivity found by the authors.
Figure 5 shows that the simulated droplet number is about 5 times smaller than observed ones in the LES. Why?
This seems to demonstrate that others microphysical processes are not correctly taken into account.

-The second concerns is the fact that some simulated parameters show significant errors with respect to observations near the surface before the adiabatic fog, except for LES where the temperature at the surface is forced : e.g
sensible heat flux (fig2), water deposition rate (fig4),downwelling lonwave radiation (fig6).
This seems to demonstrate that the coupling between the land-surface and atmosphere is not correctly simulated.
Moreover, the evolution of observed profiles between 0000UTC and 0030UTC seems to demonstrate that processes at the fog top play a key role in the onset of adiabatic fog (local advection? KH waves?).
The simulated temperature at 100m of LES also showed significant errors at 100m with respect to tethered balloon (fig3, fig10).
Why?
This seems to demonstrate that processes at the top of the fog layer are not correctly simulated.

Given these remarks, the proposed modifications look like a way to compensate model misrepresentation of dynamical processes.
These modifications are efficient for UKV (fig12). But is it specific to this model (due to errors in other parameterisations)?

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ED: Reconsider after major revisions (24 Apr 2018) by Yafang Cheng

AR by Ian Boutle on behalf of the Authors (04 May 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (08 May 2018) by Yafang Cheng

RR by Thierry Bergot (17 May 2018)

ED: Publish as is (17 May 2018) by Yafang Cheng

AR by Ian Boutle on behalf of the Authors (17 May 2018)

Short summary

Aerosol processes are a key mechanism in the development of fog. Poor representation of aerosol–fog interaction can result in large biases in fog forecasts, such as surface temperatures which are too high and fog which is too deep and long lived. A relatively simple representation of aerosol–fog interaction can actually lead to significant improvements in forecasting. Aerosol–fog interaction can have a large effect on the climate system but is poorly represented in climate models.