Characterization of transport regimes and the polar dome during Arctic spring and summer using in situ aircraft measurements

Bozem, Heiko; Hoor, Peter; Kunkel, Daniel; Köllner, Franziska; Schneider, Johannes; Herber, Andreas; Schulz, Hannes; Leaitch, W. Richard; Aliabadi, Amir A.; Willis, Megan D.; Burkart, Julia; Abbatt, Jonathan P. D.

doi:https://doi.org/10.5194/acp-19-15049-2019

Articles | Volume 19, issue 23

https://doi.org/10.5194/acp-19-15049-2019

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

Special issue:

NETCARE (Network on Aerosols and Climate: Addressing Key Uncertainties...

https://doi.org/10.5194/acp-19-15049-2019

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

Articles | Volume 19, issue 23

Research article

|

13 Dec 2019

Research article |

| 13 Dec 2019

Characterization of transport regimes and the polar dome during Arctic spring and summer using in situ aircraft measurements

Heiko Bozem, Peter Hoor, Daniel Kunkel, Franziska Köllner, Johannes Schneider, Andreas Herber, Hannes Schulz, W. Richard Leaitch, Amir A. Aliabadi, Megan D. Willis, Julia Burkart, and Jonathan P. D. Abbatt

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Final revised paper (published on 13 Dec 2019)
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RC1: 'Review of Characterization of Transport Regimes and the Polar Dome during Arctic Spring and Summer using in-situ Aircraft Measurements, by H. Bozem et al.', Anonymous Referee #1, 06 Mar 2019
- AC1: 'Response to Reviewer 1', Heiko Bozem, 08 Aug 2019
RC2: 'Review of «Characterizing of Transport Regimes and the Polar Dome during Arctic Spring and Summer using in-situ Aircraft Measurements” by H. Bozem et al.', Anonymous Referee #2, 16 Mar 2019
- AC2: 'Response to Reviewer 2', Heiko Bozem, 08 Aug 2019

Peer-review completion

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

AR by Heiko Bozem on behalf of the Authors (05 Sep 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (06 Sep 2019) by Lynn M. Russell

RR by Anonymous Referee #2 (12 Sep 2019)

RR by Anonymous Referee #1 (17 Sep 2019)

Suggestions for revision or reasons for rejection

Review of "Characterization of transport regimes and the polar dome during Arctic spring and summer using in-situ aircraft measurements" by H. Bozem et al.

The revised manuscript is much improved and the structure allows for a more logical flow. Thanks very much for undertaking the substantial task of reorganization.

The manuscript now places the analysis in a somewhat broader context, so the scope should be more relevant to more readers. With corrections and responses to minor comments as indicated below, it should be suitable for publication in ACP. I have two more substantial remaining concerns. The first is the need to clarify some terms that are not well defined--the "polar dome" vs "Arctic front". These are used somewhat interchangeably. Are they really the same thing, and if not, how do they differ? This needs a paragraph to explain their relationship. The second is related; it is the concept of springtime transport of pollution "into the Arctic airmass" from midlatitude sources. My understanding is that the Arctic front meanders southward and emissions from high midlatitude sources can directly enter the Arctic airmass--and presumably within the "polar dome" as well. This is not really transport "to" the Arctic. It would be good to see these two topics, which are closely related, explicitly adressed in a couple of short paragraphs in the Introduction. Then these concepts should be discussed with consistent terminology throughout the text.

1) p.1,line 3, change "transport barrier" to "barrier to horizontal transport"
2) p. 1, line 6, hyphenate "aircraft-based"
3) p. 1, line 11, hyphenate "gas-based"
4) p. 2, line 2, hyphenate "amine-containing"
5) p. 2, line 2, change to "from Arctic marine biogenic sources"
6) p. 2, line 10, hyphenate "tracer-based"
7) p. 2., line 15, change to "Rising temperatures, increasing twice as fast"
8) p. 2, line 19, change to "several studies base on either in situ or"
9) p. 3, line 4, change "supposed" to "expected"
10) p. 3, line 5, change "Unusual" to "Unusually"
11) p. 3, line 10, remove the comma.
11) p. 3. Explain the relationship between the Arctic front and the polar dome. Is the polar dome the entire dome-shaped structure, while the Arctic front is the surface manifestation of the polar dome? Is one strictly based on thermal structure while the other is a barrier to transport? Are they sometimes the same and sometimes not? This ambiguity should be directly addressed in this section. It also should be clarified in the discussion at the end.
12) p. 3, line 31. Fast uplift can also be generated by synoptic-scale processes such as warm conveyor belts, not just by convection
13) p. 4, line 1. A meteorologist would probably put the words "Arctic front" here instead of "polar dome". Again, this tension should be explicitly addressed
14). p. 4, line 8. ". . . as those air masses are cold enough to enter the high Arctic lower troposphere." Perhaps a better description is that the polar dome (Arctic air mass) wobbles over high-midlatitude sources, allowing pollution to be emitted directly into the polar dome. Do you agree?
15) p. 4, line 20, remove "convective"
16) p. 4, lines 30-33. Again, ambiguity in the relationship between the polar dome boundary and the Arctic front.
17) p. 5, line 3, hyphenate "tracer-based"
18) p. 5, line 4, remove "(Section 2,3,4)"
19) p. 5, line 11, remove "climate"
20) p. 5, line 11, hyphenate "aircraft-based"
21) p. 5, line 19, define "polynya"
22) p. 6, line 2, define "PAMARCMiP"
23) p. 6, line 19, remove "In the rear section of the instrument," (not necessary)
24) p. 7, lines 1-2, remove the sentence beginning, "From the AIMMS-20 data set, . . . ." (not needed)
25) p. 7, lines 11-14, remove sentences beginning "We calculated. . ." and "These instrumental drifts . . . ." and just state the total uncertainty in the following sentence.
26) p. 7, line 14, remove "Hence"
27) p. 7, line 18, hyphenate "temperature-controlled"
28) p. 7, line 20, remove sentence beginning "The instrument itself was mounted . . . " (unnecessary detail)
29) p. 7, line 24, remove the sentence beginning "Using the same methodology as for CO. . . "
30) p. 8, line 2, is this the bulk or gradient Richardson number?
31) p. 10, line 6, is this really transport into the Arctic lower troposphere, or movement of the polar dome over emission sources?
32) Fig. 4 caption, what sort of running means are the lines (calculated over how many points?)
33) p. 11, line 2, CO increases not only because the sink (OH) decreases, but because there are continuing sources in the Arctic air mass as the front wobbles over emission regions.
34) p. 11, line 6, not only are there seasonally smaller emission of CO in midlatitude sources, but there is less emission directly in to the polar dome because the Arctic air mass does not wobble over these sources (it's too far poleward)
35) p. 12, line 3, define "low-valued" and change "isentrops" to "isentropes". Many isentropes reach the surface; how do you determine which ones define the polar dome boundary? Is it where there is a steep surface gradient in isentropes (i.e., the Arctic front)? Again, this is related to the ambiguity in defining the polar dome vs. the Arctic front that needs to be addressed.
36) p. 14, line 4, hyphenate "tracer-based"
37) p. 15, line 4, remove "now"
38) p. 15, line 5, remove "Hence,"
39) p. 17, line 10, hyphenate "tracer-derived"
40), p. 17, line 14, hyphenate "tracer-derived"
41) p. 18, line 4, insert comma after "Willis et al., (2019)"
42) p. 18, line 4, hyphenate "altitude-dependent"
43) p. 20, line 5, hyphenate "low-level"
44) p. 21, Fig. 12. The trajectories in Fig. 12c are plotted against which axis, the left or the right? Make clear in the figure caption. The caption describes panels c and d as a "vertical cross section" but there is no altitude axis in either; they are time-pressure cross sections, I guess.
45) p. 23, line 17, change "week" to "weak"
46) p. 26, figure caption. In the last sentence of the caption, I don't see any obvious "enhancement in BC" within the polar dome in panel d. It just looks relatively uniformly speckled, and tending toward the blue colors (lower BC values)
47) p. 27, lines 15-18. Here you seem to distinguish between the polar dome boundary and the Arctic front. You say "in comparison to the location of the Arctic front, our analysis. . . ." What position of the Arctic front are you talking about? A climatological position? A position for the NETCARE time period? Wouldn't one expect movement of either/both with synoptic-scale disturbances?
48) p. 28, line 2, hyphenate "transport-controlled"
49) p. 28, line 21, change to "is clearly separate"
50) p. 28, line 30, change to "can be identified based on "
51) p. 29, line 3, hyphenate "tracer-derived"
52) p. 29, line 5, change to "is separate from"

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ED: Publish subject to minor revisions (review by editor) (17 Sep 2019) by Lynn M. Russell

AR by Heiko Bozem on behalf of the Authors (26 Sep 2019) Author's response Manuscript

ED: Publish as is (01 Oct 2019) by Lynn M. Russell

AR by Heiko Bozem on behalf of the Authors (05 Oct 2019)

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Short summary

We present airborne trace gas measurements in the European and Canadian Arctic for July 2014 and April 2015. Based on CO and CO₂ in situ data as well as 10 d kinematic back trajectories, we characterize the prevailing transport regimes and derive a tracer-based diagnostic for the determination of the polar dome boundary. Using the tracer-derived boundary, an analysis of the recent transport history of air masses within the polar dome reveals significant differences between spring and summer.