Acceleration of the southern African easterly jet driven by the radiative effect of biomass burning aerosols and its impact on transport during AEROCLO-sA

Chaboureau, Jean-Pierre; Labbouz, Laurent; Flamant, Cyrille; Hodzic, Alma

doi:https://doi.org/10.5194/acp-22-8639-2022

Articles | Volume 22, issue 13

https://doi.org/10.5194/acp-22-8639-2022

© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue:

New observations and related modelling studies of the aerosol–cloud–climate...

https://doi.org/10.5194/acp-22-8639-2022

© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 22, issue 13

Research article

|

05 Jul 2022

Research article |

| 05 Jul 2022

Acceleration of the southern African easterly jet driven by the radiative effect of biomass burning aerosols and its impact on transport during AEROCLO-sA

Jean-Pierre Chaboureau, Laurent Labbouz, Cyrille Flamant, and Alma Hodzic

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Final revised paper (published on 05 Jul 2022)
Preprint (discussion started on 30 Mar 2022)

Interactive discussion

Status: closed

RC1:
'Comment on acp-2022-233', Anonymous Referee #1, 22 Apr 2022

Summary comments:

In this manuscript, the authors use two convection-permitting simulations one taking into account the BBA radiative effect and the other not to address the direct and semi-direct effects of BBA over southern Africa and the southeast Atlantic during the AEROCLO-sA field campaign in September 2017.

Both simulations are examined against satellite, airborne and ground-based observations and ECMWF analyses. Efforts are made to understand the acceleration of the southern components of the African Easterly Jet.

There is no doubt that such a comparison adds value to understanding the overall dynamic of AEJ-S and heat low, which are linked to the direct radiative effect over Angola and Namibia. However, there are numerous (sometimes major) concerns with the analysis and approach. Therefore, I encourage the authors to significantly revise the paper.

Abstract:

The readability of the Abstract may be improved by using scientifically relevant terms such as "baroclinicity" and highlighting key mechanisms in general terms rather than discussing specific simulations issues.

Introduction :

The introduction is quite good and correctly motivates the study. But there are less relevant sentences and less citations. I strongly recommend looking at the introduction in a direct and succinct way to properly motivate the questions you hope to answer.

Data:

It is not clear why only September 2017 was used in the study. Please explain why.

Results section:

The dynamic and corresponding mathematical framework (e.g., Radiative heating, temperature gradient etc.) used in this study is unclear and makes it very difficult to understand the attributions/mechanisms for the differences in the AEJ-S intensity. Improvements are necessary here.

The authors need to clarify the method used to define the AEJ-S core to produce Figure 3. Also, clarification should be provided on why 8 m/s was used to identify AEJ-S.

Refine the colour bar in Figure. 1 so that all colours are used.

Clarify by explicitly writing the equation/formula used to create Figure5.

Section 3 was essentially descriptive and was correct. Section 4 deals with the direct effects of the BBA on the atmosphere - radiation distribution and circulation and have a better-developed process approach. I like your analyses. The main concern I have is about the perspective of coupling within the atmosphere (radiation, transport, rain and convection), in that the acceleration of the AEJ-S is associated with radiative heating and increases the temperature through the intensity of the thermal heat low and gradient in temperature. So there must be some relationship and consistency among the sections 3 and 4 analyses.

Citation: https://doi.org/10.5194/acp-2022-233-RC1
- AC1: 'Reply on RC1', Jean-Pierre Chaboureau, 20 May 2022
  
  The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-233/acp-2022-233-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/acp-2022-233-AC1
RC2:
'Comment on acp-2022-233', Anonymous Referee #2, 22 Apr 2022

Please see the reviewer comments in the attached pdf as a supplement.

Citation: https://doi.org/10.5194/acp-2022-233-RC2
- AC2: 'Reply on RC2', Jean-Pierre Chaboureau, 20 May 2022
  
  The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-233/acp-2022-233-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/acp-2022-233-AC2
EC1:
'Comment on acp-2022-233', Paquita Zuidema, 29 May 2022

Dear authors -
Both reviewers recommended major revisions, with the 2nd referee suggesting an additional review. As such I am asking the same referees to reevaluate the manuscript. I personally think you have done a good job addressing the referee concerns. The writing is more polished, and the additional work of adding in additional simulations to generate ensembles is valuable and appreciated. I do have some small additional comments of my own on the revised version, listed below.
P. 2 line 35: ‘an increase’ in what?

p.2 line 39: the changes in regional circulation also affects aerosol transport over the SEA of course….e.g. the ability to reach south America (Holanda et al., 2020, ACP https://acp.copernicus.org/articles/20/4757/2020/).
fig. 4 e and f: wind vectors difficult to read.
p. 12 line 258: remove ‘there’
P. 15 line 300: What is the night-time cooling effect? Smoke doesn’t have a long wave signature. Is this from water vapor? Is an altered water vapor transport also a feature of the AEJ-S in these simulations?
p. 15 line 309: an -> a
p. 15, line 318: is this really self-lofting, or is the air within the AEJ-S more vertically mixed, so that there is less thermal stratification discouraging the same buoyancy? I can't quite tell from the potential temperature lines.
P. 19 line 386: ‘In consistency with a’ -> ‘consistent with’
the authors may also want to consider how this work relates to Kuete et al., 2021 https://link.springer.com/article/10.1007/s00382-019-05072-w. In addition Ryoo et al 2021 https://acp.copernicus.org/articles/21/16689/2021/ provides some climatological context for the focus on September 2017 (mainly shows September 2017 had a slightly weaker AEJ-S than the climatological mean.) should that be of interest.

Citation: https://doi.org/10.5194/acp-2022-233-EC1
- AC3: 'Reply on EC1', Jean-Pierre Chaboureau, 16 Jun 2022
  
  The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-233/acp-2022-233-AC3-supplement.pdf
  
  Citation: https://doi.org/10.5194/acp-2022-233-AC3

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Jean-Pierre Chaboureau on behalf of the Authors (20 May 2022) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (29 May 2022) by Paquita Zuidema

RR by Anonymous Referee #2 (13 Jun 2022)

Suggestions for revision or reasons for rejection

Review of the revised manuscript of “Acceleration of the southern African easterly jet driven by radiative effect of biomass burning aerosols and its impact on transport during AEROCLO-sA” by Chaboureau et al.

The authors have made major changes in their revised manuscript, especially by adding ensemble members and thereby providing the needed confidence in the presented results and analysis. They also addressed most of my previous comments satisfactorily in their revisions and review responses. The literature review part is also improved, and the writing is overall clearer and more coherent than it was before. I recommend the publication of the revised manuscript in ACP.

I only have minor/editorial comments below that should be considered before publication:

Figure 6: The changes in extinction between the BBRAD and NORAD are explained using the back-trajectory analysis of the air masses observed along LNG track. I wonder if there is also a role of associated water vapor transport that is causing the differences in extinction? For example, are the AOD and extinction differences between BBRAD and NORAD due to more smoke mass being transported in BBRAD at these levels or the humidity is also higher in BBRAD plume than NORAD? It would be interesting to add a panel here or elsewhere, depicting the changes in specific humidity/ RH between BBRAD and NORAD along AEJ-S.

Line 247: “Note that no dust is simulated along the leg for both simulations.” This sentence is confusing. Did you mean that “no dust” is observed in the simulations even though the track is off of Namibe or did you not include the dust component for these simulations? In that case, is it a different set of simulations than presented elsewhere?

Line 352: “Another semi-direct effect of BBA on deep convection”. Replace/omit “semi-direct”

Figure 12: The figure caption does not refer to the correct figure panels. It would also be useful to add the name of the location (Ascension Island, São Tomé, St. Helena, and Walvis Bay) on each profile panel.

Line 422: “globally” -> overall. It is not a global simulation.

Hide

RR by Anonymous Referee #3 (16 Jun 2022)

ED: Publish subject to minor revisions (review by editor) (16 Jun 2022) by Paquita Zuidema

AR by Jean-Pierre Chaboureau on behalf of the Authors (16 Jun 2022) Author's response Author's tracked changes Manuscript

ED: Publish as is (17 Jun 2022) by Paquita Zuidema

AR by Jean-Pierre Chaboureau on behalf of the Authors (21 Jun 2022) Manuscript

Short summary

Ground-based, spaceborne and rare airborne observations of biomass burning aerosols (BBAs) during the AEROCLO-sA field campaign in 2017 are complemented with convection-permitting simulations with online trajectories. The results show that the radiative effect of the BBA accelerates the southern African easterly jet and generates upward motions that transport the BBAs to higher altitudes and farther southwest.