Surface roughness during depositional growth and sublimation of ice crystals

Voigtländer, Jens; Chou, Cedric; Bieligk, Henner; Clauss, Tina; Hartmann, Susan; Herenz, Paul; Niedermeier, Dennis; Ritter, Georg; Stratmann, Frank; Ulanowski, Zbigniew

doi:https://doi.org/10.5194/acp-18-13687-2018

Articles | Volume 18, issue 18

https://doi.org/10.5194/acp-18-13687-2018

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

https://doi.org/10.5194/acp-18-13687-2018

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

Articles | Volume 18, issue 18

Research article

|

27 Sep 2018

Research article |

| 27 Sep 2018

Surface roughness during depositional growth and sublimation of ice crystals

Jens Voigtländer, Cedric Chou, Henner Bieligk, Tina Clauss, Susan Hartmann, Paul Herenz, Dennis Niedermeier, Georg Ritter, Frank Stratmann, and Zbigniew Ulanowski

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Final revised paper (published on 27 Sep 2018)
Supplement to the final revised paper
Preprint (discussion started on 18 Apr 2018)
Supplement to the preprint

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of acp-2018-254', Anonymous Referee #1, 17 May 2018
- AC1: 'Reply to Anonymous Referee #1', Zbigniew Ulanowski, 12 Jul 2018
RC2: 'Interactive comment on “Surface roughness during depositional growth and sublimation of ice crystals” by Cedric Chou et al.', Anonymous Referee #2, 27 May 2018
- AC2: 'Reply to Anonymous Referee #2', Zbigniew Ulanowski, 12 Jul 2018
RC3: 'Review of "Surface roughness during depositional growth and sublimation of ice crystals"', Anonymous Referee #3, 08 Jun 2018
- AC3: 'Reply to Anonymous Referee #3', Zbigniew Ulanowski, 12 Jul 2018

Peer-review completion

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

AR by Zbigniew Ulanowski on behalf of the Authors (16 Jul 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (24 Jul 2018) by Daniel J. Cziczo

RR by Anonymous Referee #1 (28 Jul 2018)

Suggestions for revision or reasons for rejection

Most of the itemized concerns made in my earlier review have been adequately addressed in the revised manuscript. A remaining sticky point concerns speculative mechanistic explanations provided by the authors. The authors’ statement (at the beginning of section 3.1) that

“Regular, smooth crystals can be grown at low supersaturation, where the growth rate is slow enough for the deposited molecules to diffuse on facets to well-separated attachment sites at steps, kinks, and ledges.”

remains problematic. As I pointed out earlier, this statement is not substantiated by any experimental evidence given in the paper. It is also inconsistent with much recent research, for example this statement from PNAS (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5240720/):

“the picture that emerges is that at 200 K disorder sets in within the top bilayer of ice … Then at 257 K the second bilayer melts and subsequently surface melting proceeds from 257 K onward.”

This implies that, in the temperature range relevant to the experiments presented in the ms, one would expect a QLL thickness somewhere between one and two bilayers. The authors’s dismissal of this concern (in their response to reviewers) is unconvincing; they claim that the QLL becomes “very low”, but the reference they cite (Conde et al, 2008) estimates QLL thicknesses on the order of 3-5 Angstroms at 230 K, i.e., in excess of one bilayer. One monolayer is (it would seem to me) easily enough to dominate ice/vapor interactions. Moreover, other workers (e.g., Kong, 2014, “Molecular investigations …”, Neshyba et al, 2016, “A quasi-liquid mediated …”, and others) have argued that ice/QLL/vapor interactions dominate the conversion of QLL to ice over a broad range of temperatures, and identify a key role to be played by the QLL in growth inhibition and supersaturation thresholds. Why are these findings relevant? Because they argue that the two primary events controlling growth of ice from vapor deposition (capture and conversion) are controlled by the QLL, at least at some temperatures relevant to the atmosphere.

In summary: The description of the surface of ice as a place where deposited molecules “diffuse on facets to well-separated attachment sites at steps, kinks, and ledges” is not consistent with the consensus view of the ice/vapor interface, and is not supported by experiments presented in the ms. One remedy is to simply remove it, since (as far as I can tell) the conclusions presented by the authors do not depend on this picture of the surface of ice. Another remedy is to to acknowledge research that points to the QLL as playing an important role. I believe the paper will have a longer citation half-life if this is done.

A very minor point:
The line referred to as “Equation (1)” is not an equation, as there is no “=“ sign in it.

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ED: Publish subject to minor revisions (review by editor) (10 Aug 2018) by Daniel J. Cziczo

AR by Zbigniew Ulanowski on behalf of the Authors (30 Aug 2018) Author's response Manuscript

ED: Publish as is (03 Sep 2018) by Daniel J. Cziczo

AR by Zbigniew Ulanowski on behalf of the Authors (05 Sep 2018) Manuscript

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Short summary

Surface roughness of ice crystals has recently been acknowledged to strongly influence the radiative properties of cold clouds such as cirrus, but it is unclear how this roughness arises. The study investigates the origins of ice surface roughness under a variety of atmospherically relevant conditions, using a novel method to measure roughness quantitatively. It is found that faster growth leads to stronger roughness. Roughness also increases following repeated growth–sublimation cycles.