Dear authors

Based on the review by Henning Löwe and my personal reading I recommend to accept your paper subject to minor revisions.



Sorting out grain size, traditional grain size, optical grain size, and effective grain size is a tedious task indeed. We went back and forth but I think we are on the good way if we follow Henning Löwe's last recommendation under B) in his review, 'So an even better polish would be to simply avoid "effective grain size" at all and replace it by "optical grain size" throughout... Anyway.'



I think this approach also fits best Ghislain Picard's recommendations and can really be applied throughout the paper (see attached). In addition, I made in the attached a few suggestions that I'd ask you to consider.

Best regards

Charles Fierz


Dear authors

Thank you for revising your manuscript considering the suggestions made by the H. Löwe and myself. I'm also glad that you could include the corrections you address in your answer. Your manuscript addresses an important topic of this special issue and is now very near completion.

However and unfortunately, I still have an issue with the sentence on lines 33-34, p2:
"Observations showed that the grain size (from visual determination) of snow crystals varies between 10 μm for fresh fallen snow and up to 3mm for aged snow (Singh, 2001)."

Indeed, somehow the sentence does not make sense to me - and I think to many snow scientists. Moreover, table 3.3 on page 108 of Singh (2001) is far from trustworthy in my view: where do this numbers come from? What is 'old snow'? etc.
Thus I would suggest to change this to either:

A) "It is well known from visual determination that the size of snow crystals and grains may vary from 0.05 up to at least 10 mm (for example, see Jordan et al., 2008 and Pomeroy and Brun, 2002)."
In my view, this sentence could also be left without referencing anybody as it is common sense!

B) "It is well known from visual determination that snow crystals reaching the ground typically range by two order of magnitudes in their maximum dimensions from 0.050 to 5 mm (Jordan et al., 2008, p.17) while depth hoar crystals can reach sizes of 10 mm or more (Pomeroy and Brun, 2002, p. 99)."

or C) if you want to reference work that is more specific to Antarctica, see Gay et al. (2002 ) below.

Thank you for considering this last suggestion.

Best regards
Charles Fierz

REFERENCES
Jordan, R. E., Albert, M. R. and Brun, E.: Physical processes within the snow cover and their parameterization, in Snow and Climate: Physical Processes, Surface Energy Exchange and Modeling, edited by R. L. Armstrong and E. Brun, pp. 12–69, Cambridge University Press, Cambridge, U.K., 2008.

Pomeroy, J. W. and Brun, E.: Physical properties of snow, in Snow Ecology: an Interdisciplinary Examination of Snow-covered Ecosystems, edited by H. G. Jones, J. W. Pomeroy, R. W. Hoham, and D. A. Walker, pp. 45–126, Cambridge University Press, Cambridge, New York., 2001.

Gay, M., Fily, M., Genthon, C., Frezzotti, M., Oerter, H. and Winther, J.-G.: Snow grain-size measurements in Antarctica, J. Glaciol., 48(163), 527–535, doi:10.3189/172756502781831016, 2002.