Contrasting extremely warm and long-lasting cold air anomalies in the North Atlantic sector of the Arctic during the HALO-(𝒜 𝒞)<sup>3</sup> campaign

Walbröl, Andreas; Michaelis, Janosch; Becker, Sebastian; Dorff, Henning; Ebell, Kerstin; Gorodetskaya, Irina; Heinold, Bernd; Kirbus, Benjamin; Lauer, Melanie; Maherndl, Nina; Maturilli, Marion; Mayer, Johanna; Müller, Hanno; Neggers, Roel A. J.; Paulus, Fiona M.; Röttenbacher, Johannes; Rückert, Janna E.; Schirmacher, Imke; Slättberg, Nils; Ehrlich, André; Wendisch, Manfred; Crewell, Susanne

doi:https://doi.org/10.5194/acp-24-8007-2024

Articles | Volume 24, issue 13

https://doi.org/10.5194/acp-24-8007-2024

© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue:

HALO-(AC)³ – an airborne campaign to study air...

https://doi.org/10.5194/acp-24-8007-2024

© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 24, issue 13

Research article

|

15 Jul 2024

Research article |

| 15 Jul 2024

Contrasting extremely warm and long-lasting cold air anomalies in the North Atlantic sector of the Arctic during the HALO-(𝒜 𝒞)³ campaign

Andreas Walbröl, Janosch Michaelis, Sebastian Becker, Henning Dorff, Kerstin Ebell, Irina Gorodetskaya, Bernd Heinold, Benjamin Kirbus, Melanie Lauer, Nina Maherndl, Marion Maturilli, Johanna Mayer, Hanno Müller, Roel A. J. Neggers, Fiona M. Paulus, Johannes Röttenbacher, Janna E. Rückert, Imke Schirmacher, Nils Slättberg, André Ehrlich, Manfred Wendisch, and Susanne Crewell

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Final revised paper (published on 15 Jul 2024)
Preprint (discussion started on 13 Apr 2023)

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-668', Anonymous Referee #1, 01 May 2023

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-668/egusphere-2023-668-RC1-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2023-668-RC1
- AC1:
  'Reply on RC1', Andreas Walbröl, 10 Jul 2023
  
  Dear reviewer,
  thank you for your detailed comments that helped us to better focus on the key message of the manuscript. Please find our answers to your comments appended (Reply_RC1.pdf).
  On behalf of all coauthors with the best regards,
  
  Andreas Walbröl
  
  Citation: https://doi.org/10.5194/egusphere-2023-668-AC1
  - AC3: 'Reply on AC1', Andreas Walbröl, 20 Jul 2023
    
    Dear reviewer,
    thank you for your patience regarding our responses. Please find our updated response appended (Reply_RC1_20230720.pdf).
    On behalf of all coauthors with the best regards,
    
    Andreas Walbröl
    
    Citation: https://doi.org/10.5194/egusphere-2023-668-AC3
RC2:
'Comment on egusphere-2023-668', Anonymous Referee #2, 28 May 2023

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-668/egusphere-2023-668-RC2-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2023-668-RC2
- AC2:
  'Reply on RC2', Andreas Walbröl, 10 Jul 2023
  
  Dear reviewer,
  we appreciate your supportive comments and also the detailed description of potential ERA5 errors. Please find our response to your comments appended (Reply_RC2.pdf).
  On behalf of all coauthors and with best regards,
  
  Andreas Walbröl
  
  Citation: https://doi.org/10.5194/egusphere-2023-668-AC2
  - AC4: 'Reply on AC2', Andreas Walbröl, 20 Jul 2023
    
    Dear reviewer,
    we have also reviewed our responses to your comments. Thank you for waiting for our updated responses which are appended (Reply_RC2_20230720.pdf).
    On behalf of all coauthors and with best regards,
    
    Andreas Walbröl
    
    Citation: https://doi.org/10.5194/egusphere-2023-668-AC4

Peer review completion

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

AR by Andreas Walbröl on behalf of the Authors (24 Jul 2023) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (25 Jul 2023) by Johannes Quaas

RR by Anonymous Referee #2 (12 Aug 2023)

RR by Anonymous Referee #1 (13 Aug 2023)

Suggestions for revision or reasons for rejection

This is a revised version of a manuscript that is expressedly intended to describe the meteorological conditions during the HALO-AC3 campaign. It started out as a very unfocused manuscript, where now some parts have been transferred to a series of Appendices. What remains, however, is still problematic and cannot be published in this form.

I’ve been struggling with what to recommend this time, and as the “unfocusedness” from the previous version was not really reduced, it tells me the author needs more incentive to think anew; hence I now recommend a rejection hoping that the material behind the manuscript can be reshaped into something coherent.

Major concerns

I think the main question here is “why”. Why write this paper and why with this content? Like I mentioned in my earlier review I do sympathize writing a summary paper from a field campaign; I’ve been there myself. It is very useful to have one as a reference for all future papers from the campaign! But it will still have to stand by itself as a science contribution.
A campaign description – which this is not – should hold something about strategy and thinking; the “how” and “why” and not just the “what”. A description of what happened is even more difficult; the science has not yet been done and just an analysis of the meteorology during a time period, just because there happened to be a field campaign during that time, is not really a good enough reason to write a science paper about. Unless some real science is actually revealed in the analysis, which is unfortunately not the case here. So while I can see the usefulness for future reference, I do not see enough science here to warrant publication in a science journal. As a project report, yes; as a paper no. Moreover, most of the data analyzed – sometimes even cleverly analyzed – is ERA5-data and not observations at all. So I struggle with why! Why should this paper be published, except for its values as a useful future reference?

In addition to this, I still find the paper poorly organized and confusing to read. Section 4 is mostly a repetition of Section 3, with the addition of the Polar Low and cirrus analysis, although both are mentioned also in section 3, and are both mostly superficial in Section 4; both sections are not needed and represents somewhat different writing structures. Above all, there is a lack of a narrative and reason; there is no connection between the developing meteorology and when the aircrafts were deployed – and how they were deployed.

The text is often confusing and different definitions are used in the different parts. For example, in Section 4, at the start on line 357, the dates 12-13, 14, 15 and 20 March are listed as having atmospheric rivers (ARs). But in Figure 3a the 14th is not classified at all and the 20th is classified as a cold-air outbreak (CAO). Looking at Figure 2 and the definitions used for an AR (lines 134-136, 60.5 kg m-1 s-1), there is one AR starting, probably, on the 12th continuing until the 17th with two “strong” peaks (line 136, > 100 kg m-1 s-1). The adopted definition moreover requires a duration of 1.5 days, which the 14, 15 and 20 March episodes would not fulfil being only one day each, and a width of 9deg which is not commented at all.

There are simply too many things that I need to question. The definition of “aged air” is very fuzzy and seemed very “hand waiving” to me. Where does it come from, what ius aging and how do you know? The use fo circles flights to detect synoptic scale divergence needs a better evaluation before being used in a descriptive paper and here it doesn’t really add any value. I suggest dropping it for now. The same goes for the sections on Ny Ålesund observations. Although these are the only atmospheric observations in this paper, it doesn’t add any value to the content. The conclusion that there is a one day difference is too simplistic to be useful and the conclusion that one needs to be careful with easterly flow is trivial.

The revised manuscript has pretty much the same unfocused and confusing structure as the original only with pieces moved to Appendices. This work needs to be uprooted and replanted; therefore my recommendation.

Detailed concerns:

Line 30: “… at most heights” is better.

Lines 32-34: The argument that the upper tropical troposphere also has an amplified warming is intriguing and interesting; however, it never leads anywhere. Follow up or drop it.

Lines 38-43: This discussion reveals a troubling, however, unpronounced conceptual model. If the warm air was to glide up on top of the cold Arctic air (line 39), where does Arctic air come from? It can exit the Arctic in CAOs but southerly air cannot make it into the Arctic because it glides on top of the cold Arctic air. Moreover, to achieve the suggested downward long wave radiation effects, requires a low cloud base with a temperature close to that of the surface or higher and ascending air cools off. Of course this is not what happens! Southerly air masses are transformed to Arctic air masses by interactions with the new surface.

Line 57-58: The sentence “This cloud … , 2018)” seems to be incomplete.

Lines 65-68: Long and complicated sentence! I suggest cutting in two: “Therefore, … the Arctic.” And then “This motivated … (AC)3”.

Lines 74-75: Operating in a quasi-Lagrangian fashion does not necessarily require longer range, although long range is always good to have. The idea is to repeat visits to the same airmass at multiple missions. The long range comes in handy when following an airmass in over the pack ice, as staging is from far away in Kiruna.

Line 81: Drop “basis”.

Line 95: This heading just must be a misrepresentation of the HALO contribution to the observations of the atmosphere!

Line 107: So which is it; a satellite pixel or a model grid cell?

Line 152: Swap: “turbulent surface heat fluxes“ is better.

Line 164: Confusing; what is referred to hear is the fact that a model cannot resolve energy at scales below several time its spatial resolution (theoretically always > 2; in practice often 5-10 times). The criteria applied here all come from the model resolved scale and including more grid points doesn’t add anything.

Line 170-172: Suggest dropping this. It is not really a proven method and the circle used is of the same scale as a Polar Low and therefore this cannot be used to detect one. The results shown here is also less than clear.

Lines 173-180: No trajectories are used in the paper, so I suggest you drop this sub-Section.

Section 3: This section moves on to the nitty-gritty much to fast. Discuss Figures 2-4 in more general terms so that the reader is familiarized with how these figures are builkt and can then use them for the more detailed description.

Lines 188-196: Mostly conentless rambling; use the space more efficiently to really motivate the division into the two main periods.

Line 198: Drop “corresponding”; not necessary.

Figure 2: Are the ticks at 00 or 12 UTC. It seems to this reviewer there is only one long AR according to the definition, with a dip in strength around the 15th.

Line 218-221: Everything here is from ERA5 so we don’t really know that temperature “was” above freezing, in fact I doubt it, and the liquid precipitation was not “documented”.

Line 224: I have a problem orienting myself here; I can’t find that “low geopotential” which “persisted”.

Line 226 and elsewhere: It is unclear to this reviewer if a “Shapiro-Keyser cyclone” is a real physical feature or just an alternative conceptual mode. In either case, drop this or explain it properly. What makes it an Shapiro-Keyser cyclone if indeed that is something different to any other extratropical cyclone or Polar Low.

Line 235: I see no evidence of how the “Arcytic inversion” looked like or was changed; this seems out of place.

Lines 248-251: These seems to be very large changes in the statistics for a change in M from 9 to 10?

Line 254: Unclear what is meant by “sub-polar” here; what air mass is this, from where does it come and what is meant by aging? And how do you know?

Line 259: Confusing; isn’t this esterly flow? Then downstream would be western Fran Strait which is ice covered and would be on-ice flow.

Line 260: Is “attribute” the right word here? This means finding the reason for; maybe use “classification”?

Line 262: What do you mean by “another weak”; the previously discussed onbes were not weak?

Lines 266-267: How can enhanced IWV predominantly due to water vapor close to the surface, where it is warm, be advected by “upper-level flow”?

Page 15, para 1: Thois whole paragraph preceeds the climatology discussion that begins in the next sub-section.

Line 289-290: I see no reason why there should be a balance here; in fact there should nopt be a balance since there has to be a climatological heat transport northward to compensate for the radiative net loss at the Arctic TOA.

Line 294: Maybe I misunderstand but I don’t see the lowest 500 hPa anomalies over Greenland?

Lines 298-299: Again, why should there be a balance and what relevance are these dates in other years?

Section 3.2 Drop this; doesn’t add anything to the manuscript.

Line 251: What are “weather related filters” and “smearing uncertainty”?

Line 365-370: It is unclear if these results and the discussion refers to ARs that start at a given latitude and ends in the Arctic or if some of them in fact ends much earlier. Colder air more northward holds less water vapor and naturally must have lower IWT.

Line 373: What do you mean by time steps?

Line 375-377: Unclear sentence starting with “While…”; why “while”?

Line 381-382: And hence their length becomes dependent on a somewhat arbitrary definition.

Figure 10: Doesn’t make any sense to me! The definition of the “deviation” by necessity makes it zero whenever the 2022 precipitation rate is zero. Presumably, the deviations can be substantial also when this is the case.

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ED: Reconsider after major revisions (15 Aug 2023) by Johannes Quaas

AR by Andreas Walbröl on behalf of the Authors (12 Apr 2024) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (12 Apr 2024) by Johannes Quaas

RR by Anonymous Referee #2 (05 May 2024)

Suggestions for revision or reasons for rejection

The manuscript flows well now and I like the figures. I remain puzzled why a manuscript focused on the HAO-AC3 field campaign contains absolutely no analysis of the HALO data. We see the dropsonde locations in Fig. 1, then on line 175 are told how scarce the measurements are and diverted to reanalysis. Why not use all the dropsondes to assess if ERA5 indeed possesses a moisture deficit, for example? It seems like a relatively easy assessment and something society funds field campaigns to do. So I feel that I am missing something - maybe the ERA5 assessment using HALO dropsonde data is a dedicated project someone else is undertaking?

I like the focus on the extremely warm AR event, it is something to organize the paper around and the authors have done that by and large. I wonder if AR1 and AR2 couldn’t simply be grouped together - although the Guan/Waliser discrimination identifies two, I don’t see the meteorology as being different and in practice they are grouped together. Just calling AR1+AR2, AR1, could simplify the writing.

The new title is an improvement in that it sounds like less of a report, but ‘Unusual’ sounds vague to me - why not try to summarize what is the unusual condition? I believe that is the AR, as the MCAOs aren’t all that extreme - the domain is still warmer in the mean after all. Thus I suggest the authors reconsider the title (or defend their current choice further), to focus more on the anomalous warmth of the conditions sampled during HALO-AC3.

Another recommendation is to highlight the large-scale circulation features further. An SLP high over Scandinavia and SLP low over Greenland flip, around March 20. A map of the entire Arctic, showing the baroclinic wave structure for the 2 regimes, would be of interest. Of further interest of course is whether the atmospheric blocking is more pronounced than climatology, to help explain the AR, if that can be done.

Line 175 ‘scarcity of measurements’ is a strange phrase here. Can this be stated in a more nuanced fashion, for example by referencing some of the genuine measurement papers?

Line 187: is the typical Arctic SLP established elsewhere in the manuscript?

Line 14 in abstract: mention the maxima values are in the ERA5 record (and not measurements)

Line 228: can ARs can start in the arctic? That seems strange.

Line 252: why not treat the reader to a radar image of the brightband here? Also include mention of whatever retrieved precipitation values are available from the HALO datasets, I would think some preliminary values at least are available, after 2 years?

Line 281: a 19 day mcao cant just be one strong cyclone passage, and it’s also hard to see the 19day extent in Fig. 4. An Arctic wide 500 hPa Geopotential height analysis, averaged over the warm and cold periods, might help bring this out.

Overall the figures are nice, Fig 7, 9, 10 in particular . Within Fig. 4, the white contour lines indicating the SLP can be a little faint. Suggest thickening a few key lines, and including ‘L’ and ‘H’ to indicate pronounced closed circulations.

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ED: Publish subject to minor revisions (review by editor) (05 May 2024) by Johannes Quaas

AR by Andreas Walbröl on behalf of the Authors (14 May 2024) Author's response Author's tracked changes Manuscript

ED: Publish as is (16 May 2024) by Johannes Quaas

AR by Andreas Walbröl on behalf of the Authors (25 May 2024) Author's response Manuscript

Short summary

To support the interpretation of the data collected during the HALO-(AC)³ campaign, which took place in the North Atlantic sector of the Arctic from 7 March to 12 April 2022, we analyze how unusual the weather and sea ice conditions were with respect to the long-term climatology. From observations and ERA5 reanalysis, we found record-breaking warm air intrusions and a large variety of marine cold air outbreaks. Sea ice concentration was mostly within the climatological interquartile range.

Contrasting extremely warm and long-lasting cold air anomalies in the North Atlantic sector of the Arctic during the HALO-(𝒜 𝒞)3 campaign

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Interactive discussion

Peer review completion

Suggestions for revision or reasons for rejection

Suggestions for revision or reasons for rejection

Suggestions for revision or reasons for rejection

Contrasting extremely warm and long-lasting cold air anomalies in the North Atlantic sector of the Arctic during the HALO-(𝒜 𝒞)³ campaign