Ice particle sampling from aircraft – influence of the probing position on the ice water content

Afchine, Armin; Rolf, Christian; Costa, Anja; Spelten, Nicole; Riese, Martin; Buchholz, Bernhard; Ebert, Volker; Heller, Romy; Kaufmann, Stefan; Minikin, Andreas; Voigt, Christiane; Zöger, Martin; Smith, Jessica; Lawson, Paul; Lykov, Alexey; Khaykin, Sergey; Krämer, Martina

doi:https://doi.org/10.5194/amt-11-4015-2018

Articles | Volume 11, issue 7

https://doi.org/10.5194/amt-11-4015-2018

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

Special issue:

ML-CIRRUS – the airborne experiment on natural cirrus...

https://doi.org/10.5194/amt-11-4015-2018

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

Articles | Volume 11, issue 7

Research article

|

11 Jul 2018

Research article |

| 11 Jul 2018

Ice particle sampling from aircraft – influence of the probing position on the ice water content

Armin Afchine, Christian Rolf, Anja Costa, Nicole Spelten, Martin Riese, Bernhard Buchholz, Volker Ebert, Romy Heller, Stefan Kaufmann, Andreas Minikin, Christiane Voigt, Martin Zöger, Jessica Smith, Paul Lawson, Alexey Lykov, Sergey Khaykin, and Martina Krämer

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Final revised paper (published on 11 Jul 2018)
Preprint (discussion started on 17 Oct 2017)

Interactive discussion

Status: closed

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

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RC1: 'Anonymous Review of amt-2017-304', Anonymous Referee #1, 13 Nov 2017
- AC1: 'Answer to all referees', Martina Krämer, 17 Mar 2018
- AC2: 'Revised Manuscript with tracked changes', Martina Krämer, 17 Mar 2018
- AC3: 'Revised manuscript', Martina Krämer, 17 Mar 2018
RC2: 'Referee Comment', Anonymous Referee #2, 26 Nov 2017
- AC1: 'Answer to all referees', Martina Krämer, 17 Mar 2018
- AC2: 'Revised Manuscript with tracked changes', Martina Krämer, 17 Mar 2018
- AC3: 'Revised manuscript', Martina Krämer, 17 Mar 2018
RC3: 'Review of the paper: “Ice particle sampling from aircraft – influence of the probing position on the ice water content” by Afchine et al.', Anonymous Referee #3, 06 Dec 2017
- AC1: 'Answer to all referees', Martina Krämer, 17 Mar 2018
- AC2: 'Revised Manuscript with tracked changes', Martina Krämer, 17 Mar 2018
- AC3: 'Revised manuscript', Martina Krämer, 17 Mar 2018

Peer-review completion

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

AR by Martina Krämer on behalf of the Authors (19 Mar 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (28 Mar 2018) by Darrel Baumgardner

RR by Anonymous Referee #3 (03 Apr 2018)

Suggestions for revision or reasons for rejection

Evaluation of the revised manuscript titled: “Ice particle sampling from aircraft – influence of the probing position on the ice water content” by Afchine et al.

The revised manuscript was improved and addressed many questions. However, these clarifications brought up other serious issues, which were hard to identify in the original submission.
1. The authors evaluate comparisons between FISH/HAI/WARAN probes (Fig.9) based on the visual assessment of proximity of the scatter points to the 1:1 line in the log-log coordinates. This assessment led to the conclusions in sections 5.1.1 and 5.1.4, like “Most of the measurements symmetrically spread around the 1:1 line within a factor of 2.5, which can be considered as a good agreement”. However, after addressing comment #7 and qualifying the relationships between the IWCs measured by FISH, HAI and WARAN it becomes clear that these dependencies are explicitly non-linear. The FISH and HAI IWCs are related as Y =0.481X+ 0.270, and FISH and WARAN IWCs correspondingly are related as Y = 0.651X+ 0.562. Here, Y and X represent log(IWC) of relevant instruments. So, the first dependence is close to a quadratic relationship between the FISH and HAI IWCs, whereas the second one is close to 3/2 power dependence between FISH and WARAN IWCs. Such relationships between measurements of the probes mounted in the same location put the accuracy of their IWC measurements into question.
2. The response to the comment #9 includes the statement “With the more detailed explanation of the methodology (Section 2) we used here, we hope it is clear now that the ’duck’ type behavior of the ratio IWC/Rice is not caused by errors in calculations of IWC from the particle probes - if that would be the case then an agreement of IWC measurements (as shown in new Fig. 9) would not be possible.” As follows from the regression equations in the figure caption to Fig.9 there is no such agreement. The relationships between the three IWC probes appear to be non-linear. This fact may put into question the results presented in Fig.12.
3. The absence of a correlation between the roof FISH/HAI/WARAN and wing NIXE-CAPS IWC measurements in Fig.10 requires an explanation. Otherwise, one may doubt the performance and operability of these instruments during the ML-CIRRUS campaign. Since this is directly related to the objective of this study, this question should be properly explored and addressed, rather than just stating the absence of correlation in section 5.1.2 as a matter of fact. The correlation coefficient between FISH and HAI (i.e. R^2=0.33) seems to be overly low too. This fact also requires explanation.

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RR by Anonymous Referee #1 (09 Apr 2018)

Suggestions for revision or reasons for rejection

Review of “Ice particle sampling from aircraft-Influence of the probing position on the ice water content.” By Afchine et al.

Recommendation: Requires revision for publication

The authors have made a number of changes in the revised manuscript, and added some CFD simulations, all of which enhance the quality of the manuscript. However, I still think that the authors are not adequately acknowledging the uncertainties associated with their results for the reasons stated below:

1) The authors categorically state that “the wing IWC is derived from the measurements of PSD_Ice, that should be only weakly influenced by flow perturbation effects.” Although it is believed that this is the case, the quality of the wing IWC will depend on exactly where the wing probes are mounted. Typically these probes are mounted as far beneath and ahead of the leading edge of the wing as possible, and there may be enhancements or shadowing of concentrations depending on the exact mounting location. Is this something the CFD simulations can address? This uncertainty in the wing IWCs must be better acknowledged rather than assuming that the wing IWC is a reference value. Further, their statement that “most favorable for an undisturbed sampling on aircraft is most likely the position under an aircraft wing” is not necessarily true as many aircraft mount the probes so that the probes are positioned ahead of the aircraft wing to get a more clear flow. The authors seems to acknowledge this to some extent later on when they state that “they are in most cases mounted below the aircraft wings with sufficient distance to the wing and aircraft body”, but they do not define what sufficient is.

2) Perhaps the greater uncertainty the calculation of the wing IWC is the use of an M-D relation to derive the IWC from a measured size distribution. This manuscript does not adequately acknowledge the uncertainty in the calculation of the IWC from a size distribution. The authors state that “a reliable agreement between IWCs from two different instruments mounted at two different positions is a reasonable indication for an applicable IWC measurement.” But, if the basis of the choice of m-D coefficients is to get better agreement with the IWCs made in another location, one is merely obtaining what one assumed in the derivation of the m-D relations. Thus, it is not surprising that the IWC_PSD agrees with the FISH IWC given that this agreement was used to justify the choice of m-D relations used: this is a bit of circular logic. This point is also made on page 13 where it states that “the good agreement between the two measurements … shows the validity of the m-D relation used to calculate the IWC from the PSD.” I also have to make a comment on Figure 8, which the authors use to state that the IWCs derived from PSDs are not very sensitive to the choice of m-D relation: note that 8 orders of magnitude are included on the vertical axis so visually there appears to be little dependence. However, some of the differences are not that small. The writing and analysis needs to be more quantitative so that it can be determined what a large and small difference is.

3) I don’t think the authors accurately describe how ice crystal bouncing might be affecting the calculation of the IWC. The authors state that shattering “does not play a significant role for the calculation of the IWC since the ice fragments contribute to the integrated mass of PSD_ice in the same way as the original large crystal.” However, this statement is not true. The shattered artifacts are typically generated from large ice crystals hitting the tips of the probes which are outside of the sample volume, with the small remnants then being swept into the sample volume. I agree that given the use of the Korolev tips, the impact of the shatter artifacts on IWC is most likely minimal.

Despite these limitations, I still think that the manuscript makes a contribution to our scientific understanding of probe position on measured IWC. However, I think the uncertainties in the work need to be better acknowledged. Further, if a more quantitative analysis of the uncertainties could be made the manuscript would read better. Further, use of terms like “significant”, “small” and “large” should be avoided and replaced with more quantitative explanations of what the differences are.

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ED: Reconsider after major revisions (11 Apr 2018) by Darrel Baumgardner

AR by Martina Krämer on behalf of the Authors (24 May 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (25 May 2018) by Darrel Baumgardner

RR by Greg McFarquhar (29 May 2018)

RR by Alexei Korolev (13 Jun 2018)

ED: Publish as is (13 Jun 2018) by Darrel Baumgardner

AR by Martina Krämer on behalf of the Authors (24 Jun 2018) Manuscript

Short summary

The ice water content (IWC) of cirrus clouds is an essential parameter that determines their radiative properties and is thus important for climate simulations. Experimental investigations of IWCs measured on board research aircraft reveal that their accuracy is influenced by the sampling position. IWCs detected at the aircraft roof deviate significantly from wing, side or bottom IWCs. The reasons are deflections of the gas streamlines and ice particle trajectories behind the aircraft cockpit.