Investigation of ice particle habits to be used for ice cloud remote sensing
for the GCOM-C satellite mission

Letu, Husi; Ishimoto, Hiroshi; Riedi, Jerome; Nakajima, Takashi Y.; C.-Labonnote, Laurent; Baran, Anthony J.; Nagao, Takashi M.; Sekiguchi, Miho

doi:https://doi.org/10.5194/acp-16-12287-2016

Articles | Volume 16, issue 18

https://doi.org/10.5194/acp-16-12287-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-16-12287-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 16, issue 18

Research article

|

29 Sep 2016

Research article |

| 29 Sep 2016

Investigation of ice particle habits to be used for ice cloud remote sensing for the GCOM-C satellite mission

Husi Letu, Hiroshi Ishimoto, Jerome Riedi, Takashi Y. Nakajima, Laurent C.-Labonnote, Anthony J. Baran, Takashi M. Nagao, and Miho Sekiguchi

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Final revised paper (published on 29 Sep 2016)
Preprint (discussion started on 11 Nov 2015)

Interactive discussion

Status: closed

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

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- Supplement

RC C9525: 'Re: formal review of acp-2015-756', Anonymous Referee #2, 19 Nov 2015
- AC C12482: 'Response to the comments of reviewer#2', Husi Letu, 17 Feb 2016
RC C9973: 'Review', Anonymous Referee #1, 01 Dec 2015
- AC C12510: 'Response to the comments of reviewer#1', Husi Letu, 18 Feb 2016

Peer-review completion

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

AR by Husi Letu on behalf of the Authors (10 May 2016) Author's response

ED: Referee Nomination & Report Request started (19 May 2016) by Jui-Yuan Christine Chiu

RR by Anonymous Referee #1 (31 May 2016)

Suggestions for revision or reasons for rejection

This is a review for the revised manuscript “Investigation of ice particle habits to be used for ice cloud remote sensing for the GCOM-C satellite mission” submitted to ACP by Letu et al.

Based on reviews of myself and the other reviewer, several changes to the manuscript are made. I thank the authors for the changes made to the manuscript so far and for clarifying some issues. I will accept the authors’ choice to include pristine ice crystals in their study.

Unfortunately, for some reason the authors missed all of my minor comments, which are repeated below. Also, the revised version that I received did not contain an abstract so I cannot judge that. The revised abstract should reflect the use of size –integrated properties now. In addition, I think the SAD method should be explained better, as explained below. After these minor corrections, I would recommend publication of the paper.

The description of the SAD method was altered. However, it is still unclear how the POLDER measurements are used in the method. The authors state that “the spherical albedo can be calculated from the Lobs in each pixel … to investigate the P11 element of ice particle models.” It is not that trivial and it is not explained how this is done. If I understand correctly, optical thickness is retrieved from the measurements at each angle and in some way the spherical albedo is derived. Please work with the experienced co-authors to describe this method more clearly.

One minor error in the revised version is in equation 6, where the area in the numerator does not seem to belong there.

Minor comments repeated from first review (page and line numbers refer to original submission):

P31669, L1: Perhaps the most important update in the 2013 version of the Yang et al. database was the addition of roughness to the particle surfaces. That should be mentioned here.

P316670, L6: The van Diedenhoven et al. (2012) paper is cited here, but this paper only describes a method to retrieve crystal roughness. Other papers by this group show the method applied to data, such as van Diedenhoven et al. (2014; already cited) and van Diedenhoven et al. (2013; ACP, vol 13, 3185-3203, doi:10.5194/acp-13-3185-2013.). These would be better references here.

P316671-72: Are the Voronoi model optical properties based on a single realization of the Voronoi habit or are several averaged? Does the geometry of this model depend on size or not?

P316673, L27: Please point out that the scattering angle ranges observed depend on latitude, possibly adding lines to the figure to show the different sampling in various latitude bands.

P316674, L2: What is meant with a “changing peak”. Please explain in the paper or rephrase. Also on page 31678.

P31677, Figure 5: The y-axis in figure 5 is such that the relevant differences between the models are not apparent. The asymmetry parameters appear to range from 0.5 to 0.9, which is a huge range in terms of radiative effects. Please change the y-axis range to at least 0.5-1 to make the differences between the models apparent.

Page 31679, L8, Fig. 9: Please explain what is meant with “averaged over all distortion values”. Which distortion values are that? 0, 0.15 and 0.25?

Page 31679, L16: Please replace “most efficient” with something like “more consistent with measurements”.

Page 31680, L2: This conclusion is consistent with the conclusion of Liu et al. (2014) that of geometric irregularity and surface roughness are effectively equivalent. Please include this citation.
(Liu, C., R. L. Panetta, and P. Yang, 2014: The effective equivalence of geometric irregularity and surface roughness in determining particle single-scattering properties. Opt. Express, 22, 23 620–23 627, doi:10.1364/OE.22.023620.)
Figure 8 and 11: These figures show similar information but for different particle types. I suggest to make the style the same so it is obvious that these are similar figures. In figure 8, the word “different” in the y-axis title (That’s corrected, but still wrong in the caption) should be “difference”.

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RR by Bryan A. Baum (14 Jun 2016)

Suggestions for revision or reasons for rejection

This revised manuscript is much improved in both content and presentation. There is one larger issue that I want to raise and a number of grammatical modifications to suggest.

Major comment:
As noted in the author responses, the choice of hexagonal columns, plates, bullet rosettes, and droxtals was simply to provide a sense of different optical properties to compare with their new particle, the Voronoi ice habit. The ice habit comparison is featured in Figures 4, 5, and 6. I think this paper would make a much larger scientific contribution if the droxtal was replaced with an aggregate of solid columns, as is used later in the manuscript. Here’s my argument for doing so. First, the droxtal was promoted initially as an idealized small circular particle to represent the smallest (<10-20 micron) particles at the top of the coldest ice clouds. It was never meant to be used for larger particles as in this paper and is an unrealistic choice for comparisons. Second, the CERES team uses a roughened solid hexagonal particle for their ice cloud retrievals and flux calculations, while the MODIS team now uses an aggregate of solid columns for the Collection 6 cloud products (reference: Holz et al., Resolving ice cloud optical thickness biases between CALIOP and MODIS using infrared retrievals, Atmos. Chem. Phys., 16, 5075-5090, 2016, doi:10.5194/acp-16-5075-2016). If the goal of this paper is to decide upon a model to use with the GCOM-C SGLI satellite sensor, then a proper comparison (and an important one) would be to compare the suggested model (e.g., Voronoi) with the roughened column used by CERES and the roughened aggregate used by MODIS. Basically, my suggestion is to replace the droxtal with the aggregate of solid columns.

Minor comments:
page 2, line 11: there’s a “pi” symbol after the word “subsequently” for whatever reason.

page 4, line 3: …using the same micro-physically consistent habit mixture model throughout the spectrum—> …using a habit mixture model based on comparisons with microphysical measurements throughout the spectrum…

page 4, line 6: the relation between —> the relationship between

page 5, line 10: size parameter is first mentioned here, but the definition is provided on line 20. Suggest moving Equation 1 to where size parameter is first mentioned.

page 6, line 5: change “is used” to “are used” because datum is singular; data are plural.

page 6, line 7: a proper reference for the thousands of size distributions is this reference:
Heymsfield, A. J., C. Schmitt, and A. Bansemer, 2013: Ice cloud particle size distributions and pressure dependent terminal velocities from in situ observations at temperatures from 0˚ to -86˚C. J. Atmos. Sci., 70, 4123-4154.

page 7, lines 27-28 and Figure 2: do the authors have any insight as to why there are 3 large peaks in Figure 2b?

page 9, lines 2-3: Is the criterium for selecting the optimal habit a value of the SAD near zero or simply a minimum value of the SAD? How much of the time is the minimum value near zero?

page 9, line 15, discussion of Figure 4: I am puzzled by the results for the asymmetry factor - my experience is that the asymmetry factor increases monotonically with size parameter (but since these results are for a fixed wavelength, the results are really increasing with particle size). Do you have any insight as to why the asymmetry factor does not increase monotonically with particle size?

page 9, line 18: suggest rewording: “the value decreases when size parameter is increasing” to “the value decreases with increasing values of the size parameter”

page 9 line 24: Voronoi habit —> Voronoi habits

page 10, line 21: I’ve read this sentence many times and cannot make sense of it - please reword: “The SRF and TRAD for all size of particles with droxtal model are largest in the all ice particle models”

page 11, one 6: air bubbles and distortion is most efficient —> air bubbles and distortion have lower SAD values than models with distortion only. (Do I have the sense of this right? If not, please reword this sentence to make it more understandable)

page 11, line 20: This sentence is awkward - please reword as it could be interpreted more than one way: “However, that for the Voronoi model is slight smaller than for the other models…”

page 11, lines 21-22: But it seems to me that the Voronoi particle seems to have a larger TRAD than the ensemble model.

page 12, line 26-28: This sentence is long and awkwardly worded. Basically it appears to me that the results of the SAD analysis indicate that the Voronoi particle has the scattering characteristics that are useful for retrievals, e.g., agreement with POLDER/PARASOL polarized reflectances, a low asymmetry parameter, and a smooth phase function. This helps to justify use of this particle for the GCOM-C mission.

About the figures, a general comment: please increase the font size for labels on the figure axes - the labels use small letters that will only decrease further in the publication. Also, it helps to use a font like Arial, Palatino, or Helvetica rather than a font like Times Roman. Second, help the reader out by increasing the amount of information in the captions. For example, in Figure 4, there is little information in the caption. What is As, for example (I think it’s single scattering albedo) - why not use SSA rather than As? Define what “g” and Qext represent in the caption.

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ED: Reconsider after minor revisions (Editor review) (27 Jun 2016) by Jui-Yuan Christine Chiu

AR by Husi Letu on behalf of the Authors (14 Aug 2016) Author's response Manuscript

ED: Reconsider after minor revisions (Editor review) (31 Aug 2016) by Jui-Yuan Christine Chiu

AR by Husi Letu on behalf of the Authors (10 Sep 2016) Author's response

ED: Publish as is (15 Sep 2016) by Jui-Yuan Christine Chiu

AR by Husi Letu on behalf of the Authors (18 Sep 2016)