Smoke of extreme Australian bushfires observed in the stratosphere over Punta Arenas, Chile, in January 2020: optical thickness, lidar ratios, and depolarization ratios at 355 and 532&thinsp;nm

Ohneiser, Kevin; Ansmann, Albert; Baars, Holger; Seifert, Patric; Barja, Boris; Jimenez, Cristofer; Radenz, Martin; Teisseire, Audrey; Floutsi, Athina; Haarig, Moritz; Foth, Andreas; Chudnovsky, Alexandra; Engelmann, Ronny; Zamorano, Félix; Bühl, Johannes; Wandinger, Ulla

doi:https://doi.org/10.5194/acp-20-8003-2020

Articles | Volume 20, issue 13

https://doi.org/10.5194/acp-20-8003-2020

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

https://doi.org/10.5194/acp-20-8003-2020

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

Articles | Volume 20, issue 13

Research article

| Highlight paper

|

10 Jul 2020

Research article | Highlight paper |

| 10 Jul 2020

Smoke of extreme Australian bushfires observed in the stratosphere over Punta Arenas, Chile, in January 2020: optical thickness, lidar ratios, and depolarization ratios at 355 and 532 nm

Kevin Ohneiser, Albert Ansmann, Holger Baars, Patric Seifert, Boris Barja, Cristofer Jimenez, Martin Radenz, Audrey Teisseire, Athina Floutsi, Moritz Haarig, Andreas Foth, Alexandra Chudnovsky, Ronny Engelmann, Félix Zamorano, Johannes Bühl, and Ulla Wandinger

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Final revised paper (published on 10 Jul 2020)
Preprint (discussion started on 04 Feb 2020)

Interactive discussion

Status: closed

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

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RC1: 'Review of Ohneiser et al. (2020)', Michael Fromm, 06 Mar 2020
- AC1: 'answer to reviews '1 and '2', Albert Ansmann, 11 May 2020
RC2: 'Review of the paper by Ohneiser et al.', Anonymous Referee #2, 05 Apr 2020
- AC2: 'answer to reviews '1 and '2', Albert Ansmann, 11 May 2020

Peer-review completion

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

AR by Albert Ansmann on behalf of the Authors (11 May 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (18 May 2020) by Manvendra Krishna Dubey

RR by Anonymous Referee #2 (18 May 2020)

RR by Michael Fromm (22 May 2020)

Suggestions for revision or reasons for rejection

Review of revised Ohneiser et al. (2020). (O20)
O20 have diligently addressed the reviewers’ concerns and questions. The work may be considered acceptable for publication after O20 address questions arising from the new material.
General:
P4, L21. “…pyroCB convection evolved over the fire areas in southeastern Australia and downwind over the Pacific...” This clearly indicates that pyroCbs occurred over the ocean. This is physically unrealistic and unsupported. Any mention of oceanic pyroCbs should be removed.
P4, L25. “Based on an extended trajectory analyses…” What is meant by |”extended”? I noticed that O20 used the HYSPLIT ensemble method for the trajectories. Is that what is meant rather than extended? Please clarify and correct the grammar.

P4, L19. Regarding O20’s description of tropospheric smoke on 10 Jan, it's still unclear to me where the smoke is distinct from clouds in this raw backscatter depiction. Clouds are at all the altitudes in the range mentioned in the text. The reader must take it on faith that there is some smoke there. If O20 want to press this point they need to show additional lidar data such as depolarization ratio.

P5, L2: “…forward trajectories…” No details on these trajectories are given. The citation only points to the general HYSPLIT page. No information on the source location, date, altitude is given. Please elaborate on the details of this analysis.

P5, L3. “…permanent diabatic heating…” What is meant by “permanent”? Please clarify.

P5, L5. “…the respective trajectories show many circular movements…” Where is this shown? This whole discussion of forward trajectories and diabatic heating is incomplete and flawed. As O20 acknowledge, HYSPLIT calculations do not and cannot account for such diabatic effects. The reader has no basis on which to follow the argument for the claimed upward movement of the smoke plume.

P5, L6. The “OMI, 2020” citation doesn’t directly provide the reader with any targeted details of the features to which O20 allude. If this is relevant to the analysis, it is suggested that some specific maps be provided.

P5, L7. “…30 January 2020 according to the backward trajectories.” It is not evident how the back trajectories show what O20 claim. The only ones shown and discussed are launched on 10Jan. Please elaborate.

P5, L11-12. “An almost monotonic ascent was recorded
with a constant rate of 1 km per day from 25 January (layer top at 22 km) to 30 January…” Is this based on PA data? If so, it would be good to show the data. If not, please explain the basis.

P5, L16. “…forward trajectory analysis…” Here again O20 refer to trajectories that are not characterized or shown. These seem to be equal in importance to the back trajectories they show. It would be important to understand the details of the forward trajectory source location, time, altitude, and length.

P6, L4, first sentence. Is the point here to suggest to the reader that other back trajectories were attempted from other smoke layers that did not make a connection to the Australia origin? This would make sense if indeed there was significant diabatic lofting of some of the smoke that ended up over PA. That would be reasonable and worth mentioning, especially considering the attention O20 devote to the discussion of the CALIPSO data.

P6, L11-14: “It should be noted that all trajectories arriving between about 11.5 and 15 km at Punta Arenas showed similar large-scale descending features (descend rate, advection speed and direction) so that continuous upward motion of the smoke by solar heating and large-scale downward motion of the air masses occurred without a significant change of air flow direction.” I don’t understand this logic. The PA observations at the end of the back trajectories suggest that they arrived under quasi-isentropic flow conditions.

P6, L15. “The respective backward trajectory analysis here… “ The only trajectory analysis shown applies to an endpoint at 12.5 km. Nothing can be inferred about the separate, higher layer from these trajectories. Are there other trajectories that are not shown?

P6, L29-30: “In contrast to the record breaking events discussed here, the smoke-related 532 nm AOT was 0.002 inMarch 2010…” This implies nothing about the source AOT. PA might have just sampled a weak, fringe of a larger plume. One could probably find some portions of the 2020 plume over PA that have very weak AOT (e.g. at the onset or evacuation of a layer blowing over PA.) While it is true that the 2010 pyroCb event was small in comparison to the 2020 event, making such a comparison of aged AOT so far downstream of two very different origins has little significance.

P8, L29. O20 mention the difference of smoke emissions from flaming vs. smoldering fires. But here we are talking about UTLS smoke that most likely came from very intense flaming connected with pyroconvection. Unless there s a point that I missed, I’d suggest removing this unnecessary statement.

P10, L11. Citation needed for this final sentence. Perhaps Peterson et al., (2018), who detailed the 12 August 2017 pyroCb event.

Technical:
P4, L30. Change “and remained” to “remained.”

P4, L30. “These smoke layer” should be “layers.”
P5, L2. “The respective air mass…” Respective of what?

P5, L7. “had an horizontal” should be “had a horizontal.”

P5, L11. “unique opportunity” What is unique and to what opportunity do O20 refer?

P6, L9. “This descend” should be “This descent.”

P9, L13. “descend rate” should be “descent rate.”

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ED: Publish subject to minor revisions (review by editor) (26 May 2020) by Manvendra Krishna Dubey

AR by Albert Ansmann on behalf of the Authors (28 May 2020) Author's response Manuscript

ED: Publish subject to minor revisions (review by editor) (15 Jun 2020) by Manvendra Krishna Dubey

AR by Albert Ansmann on behalf of the Authors (17 Jun 2020) Author's response Manuscript

ED: Publish as is (18 Jun 2020) by Manvendra Krishna Dubey

AR by Albert Ansmann on behalf of the Authors (18 Jun 2020) Manuscript

Short summary

Unique lidar observations of a strong perturbation in stratospheric aerosol conditions in the Southern Hemisphere caused by the extreme Australian bushfires in 2019–2020 are presented. One of the main goals of this article is to provide the CALIPSO and Aeolus spaceborne lidar science teams with basic input parameters (lidar ratios, depolarization ratios) for a trustworthy documentation of this record-breaking event.