Comparisons of bispectral and polarimetric retrievals of marine boundary layer cloud microphysics: case studies using a LES–satellite retrieval simulator

Miller, Daniel J.; Zhang, Zhibo; Platnick, Steven; Ackerman, Andrew S.; Werner, Frank; Cornet, Celine; Knobelspiesse, Kirk

doi:https://doi.org/10.5194/amt-11-3689-2018

Articles | Volume 11, issue 6

https://doi.org/10.5194/amt-11-3689-2018

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

https://doi.org/10.5194/amt-11-3689-2018

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

Articles | Volume 11, issue 6

Research article

|

26 Jun 2018

Research article |

| 26 Jun 2018

Comparisons of bispectral and polarimetric retrievals of marine boundary layer cloud microphysics: case studies using a LES–satellite retrieval simulator

Daniel J. Miller, Zhibo Zhang, Steven Platnick, Andrew S. Ackerman, Frank Werner, Celine Cornet, and Kirk Knobelspiesse

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Final revised paper (published on 26 Jun 2018)
Preprint (discussion started on 15 Sep 2017)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of Comparisons of bispectral and polarimetric cloud microphysical retrievals using LES-Satellite retrieval simulator', Anonymous Referee #1, 04 Oct 2017
- AC1: 'Author Response to Anonymous Reviewer 1', Daniel Miller, 16 Jan 2018
RC2: 'Review', Anonymous Referee #2, 27 Nov 2017
- AC2: 'Author Response to Anonymous Reviewer 2', Daniel Miller, 16 Jan 2018

Peer-review completion

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

AR by Daniel Miller on behalf of the Authors (05 Mar 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (09 Mar 2018) by Manfred Wendisch

RR by Anonymous Referee #2 (12 Mar 2018)

RR by Anonymous Referee #1 (15 Mar 2018)

Suggestions for revision or reasons for rejection

The authors did a good job in answering the reviewers questions and addressing necessary changes. There is only one issue I'm still struggling with. The new vertical weighting functions considering multiple scattering are a good improvement for the study. However, I still have doubts that this approach does provide the correct solution which is needed to quantify the retrieval biases, which is the main purpose of the manuscript.

1) To find the suitable factors $b$, the authors did compare the biases using different values of $b$ and finally chose the value which provides the best agreement between retrieval results and the vertical weighted values. In my understanding this is aiming for "moving target". You can not adjust the weighting functions in a way that the correct results are obtained. Doing so, you already rule out any source of uncertainty related to the vertical structure of the cloud.

Additionally, the authors conclude that the new 2WT weighting function using $b=9$ is similar to the old 2WT weighting function ($b=0$). Can this be explain to be the general case? I don't think this is a general rule. It might only be coincidental due to the profile of $R_{\rm e}$ applied here.

(By the way, the link to the histograms did not in the PDF.)

2) The treatment of clouds with $\tau<5$ is arbitrary in my point of view. The weighting function can not simply be changed just because the bias becomes to large. You need to give a reason why the vertical weighting function of clouds smaller than $\tau<5$ is not correct. An I do not see a reason why the concept of the multiple scattering weighting function does not hold for lower tau. Did you normalize the weighting function appropriately?

3) The authors argue, that their new weighting function considers the inhomogeneous cloud vertical structure compared to the approach by Platnick (2000). Here I disagree. Of course the simulations in the Platnick (2000) approach to calculate the weighting function assumes homogeneous clouds. But the application of the weighting functions can be done for real cloud profiles. The 2WT weighting used by the authors does the same. The 2WT weighting function is also calculated only as a function of $\tau$. Therefore, also here no profile of $R_{\rm e}$ is considered in the calculation. Only when the 2WT weighting is applied to the cloud profile the vertical structure is considered. This is similar to Platnick (2000) and in my point of view no reason to prefer the 2WT weighting functions.
I see, that it would be a big effort to completely change the weighting functions to Platnick (2000). In order not to need to do this, the authors should convincingly show, that their weighting functions are similar to the Platnick (2000) approach and do not cause any bias, that may affect the study. Such a comparison for only one or some representative cloud profiles could also be used to justify the values of $b$.

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ED: Reconsider after major revisions (16 Mar 2018) by Manfred Wendisch

AR by Daniel Miller on behalf of the Authors (27 Apr 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (05 May 2018) by Manfred Wendisch

RR by Anonymous Referee #1 (17 May 2018)

ED: Publish subject to technical corrections (17 May 2018) by Manfred Wendisch

AR by Daniel Miller on behalf of the Authors (24 May 2018) Manuscript

Short summary

Prior satellite comparisons of bispectral and polarimetric cloud droplet size retrievals exhibited systematic biases. However, similar airborne instrument retrievals have been found to be quite similar to one another. This study explains this discrepancy in terms of differing sensitivity to vertical profile, as well as spatial and angular resolution. This is accomplished by using a satellite retrieval simulator – an LES cloud model coupled to radiative transfer and cloud retrieval algorithms.