A module to convert spectral to narrowband snow albedo for use in climate models: SNOWBAL v1.2

van Dalum, Christiaan T.; van de Berg, Willem Jan; Libois, Quentin; Picard, Ghislain; van den Broeke, Michiel R.

doi:https://doi.org/10.5194/gmd-12-5157-2019

Articles | Volume 12, issue 12

https://doi.org/10.5194/gmd-12-5157-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/gmd-12-5157-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 12, issue 12

Model description paper

|

11 Dec 2019

Model description paper |

| 11 Dec 2019

A module to convert spectral to narrowband snow albedo for use in climate models: SNOWBAL v1.2

Christiaan T. van Dalum, Willem Jan van de Berg, Quentin Libois, Ghislain Picard, and Michiel R. van den Broeke

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Final revised paper (published on 11 Dec 2019)
Supplement to the final revised paper
Preprint (discussion started on 30 Oct 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 van Dalum et al.', Anonymous Referee #1, 03 Dec 2018
RC2: 'Comments of the reviewer 2', Alexander Kokhanovsky, 18 Dec 2018
RC3: 'Comments from reviewer #3', Anonymous Referee #3, 27 Dec 2018
AC1: 'Author response to referee comments 1-3', Christiaan van Dalum, 06 Feb 2019

Peer-review completion

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

AR by Christiaan van Dalum on behalf of the Authors (06 Feb 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (13 Feb 2019) by Didier Roche

RR by Kristian Pagh Nielsen (16 May 2019)

ED: Reconsider after major revisions (20 May 2019) by Didier Roche

AR by Christiaan van Dalum on behalf of the Authors (27 Aug 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (30 Aug 2019) by Didier Roche

RR by Kristian Pagh Nielsen (11 Sep 2019)

Suggestions for revision or reasons for rejection

It is very good to see that my two main comments have now been addressed, i.e. the comment regarding to account for at least the typical spectral snow albedo in the radiative transfer computations, and the comment regarding accounting for the spectral effects of variable integrated atmospheric water vapour. The authors still disagree regarding the third comment in my previous review on cloud ice equivalent radii. The manuscript should not be rejected due to this; since this is a discussion paper, the disagreement can well be left as it is! At the end of this comment, I have added a more detailed reply regarding this discussion.

The paper should be accepted when the following minor issues are corrected:

- Page 6, lines 13-14: "For this part, a spectral albedo curve depending on SZA would be more suitalbe, but limitations in DISORT prevent this." DISORT does not have such limitations, in particular with the improvements made to DISORT3 (Lin et al. 2015), this radiative transfer solver can handle the full Bi-directional Reflectance Distributions Function (BRDF) representation of surface reflectance. The words about "limitations in DISORT" should be removed from the text!

- Page 11, line 17: "In DISORT, the PW can be varied..." DISORT is a radiative transfer solver that takes layered optical properties as input. Integrated water vapour and other physical quantities is not varied in DISORT. The authors have used DISORT as fed by the libRadtran scripting system, which ensures that the physical quantities are computed into optical properties for the DISORT solver. Thus, it is in the libRadtran scripting system that the integrated water vapour can be varied. Here, and elsewhere, the text should be corrected to separate the preprocessing done in libRadtran and the computations in DISORT.

- Section 3.2 and elsewhere: The term "Precipitable water/PW", should be replaced with: "Integrated water vapour/IWV". The authors already use the correct term "water vapour" elsewhere in the manuscript. The term "precipitable water" is physically incorrect, since not all water vapour in an atmospheric column is "precipitable". Also, when precipitation occurs it is often gathered from a large area surrounding each model column, e.g. via a convective cell or cyclone structure. It does not only come from the column itself, which the term "precipitable water" implies. The term "integrated water vapour" is an accurate description of this variable.

Reference:

Lin, Z. et al. (2015): "Improved discrete ordinate solutions in the presence of an anisotropically reflecting lower boundary: Upgrades of the DISORT computational tool." Journal of Quantitative Spectroscopy & Radiative Transfer, http://dx.doi.org/10.1016/j.jqsrt.2015.02.014
, 157: 119–134.

-o-

The following text, is not something that the authors need to address. It is just my comment on the cloud ice equivalent radius discussion:

The authors maintain that 20 µm is a reasonable equivalent radius for cloud ice particles. In their reply they refer specifically to publications by King et al. (2004), Subenrauch et al. (2013) and Fitzpatrick et al. (2003). They also make it clear that they find the study of Fu et al. (1996) to be outdated. What is interesting here, is that the Fu et al. (1996) parametrization is what is used in their own climate model radiation scheme (IFS cy33r1), as I pointed out in my previous review, and that this is used in virtually all comtemporary climate and weather models that use the different generations of IFS radiation schemes up to the current ECrad scheme (Hogan and Bozzo 2018). If the authors are correct in their assertion, a general cloud ice microphysics issue exists in all these models with respect to the radiative computations!

Reference: Hogan, R. J. & A. Bozzo (2018): "A flexible and efficient radiation scheme for the ECMWF model." J. Adv. Modeling Earth Sys.

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ED: Reconsider after major revisions (18 Sep 2019) by Didier Roche

AR by Christiaan van Dalum on behalf of the Authors (25 Sep 2019) Author's response Manuscript

ED: Publish as is (23 Oct 2019) by Didier Roche

AR by Christiaan van Dalum on behalf of the Authors (30 Oct 2019) Manuscript

Short summary

Climate models are often limited to relatively simple snow albedo schemes. Therefore, we have developed the SNOWBAL module to couple a climate model with a physically based wavelength dependent snow albedo model. Using SNOWBAL v1.2 to couple the snow albedo model TARTES with the regional climate model RACMO2 indicates a potential performance gain for the Greenland ice sheet.