This is a challenging and valuable paper to attempt to clarify the sea ice break-up processes and resultant floe size distributions through wave-ice interaction from “artificial” field experiments. By inducing waves with a cruising ship, how waves broke sea ice floes was monitored by a drone. This experiment was conducted in winter and summer, and the results were assessed to improve the understanding of the break-up processes of sea ice and the generation of floe size distribution. The major findings are the importance of the ice rigidity as well as wavelength to determine the maximum floe size, much slower propagation speed of ice break-up compared with the expected wave propagation speed, and the influence of ice thickness on the wave attenuation. They also proposed a new method to represent the floe size distribution.
It is well known that the floe size distribution is one of the key parameters of sea ice and the ice break-up processes due to waves play an important role in its formation. However, due to logistical difficulties, it has been quite difficult to clarify the break-up processes from in-situ observations. To my knowledge, this is the first experiment conducted in the real sea ice area under the idealized conditions. Therefore, basically I support this work and recommend publication. Having said that, I feel some descriptions seem confusing and need to be reconsidered. For me, some conclusions are not necessarily clear. I would appreciate it if the authors address them before publication. If it comes from the lack of my knowledge or my misunderstanding, please forgive me. My major concerns are as follows:
1) Measurement accuracy.
In this experiment, ice thickness is one of the key parameters. Therefore, I think the measurement method and accuracy should be described clearly. To my understanding, it was obtained from the ice chart for GSL (L134) and from meter stick (L147-148). Since the description is only brief, I wonder if it is possible to use these data obtained from different sources equally for quantitative assessment. Some additional descriptions to guarantee it would be desirable. Besides, the horizontal scale seems to have been determined only from the FOV of the camera and the flight height of the drone (L127-128). Since the view angle and flight height could contain some ambiguities, it would be ideal to check the horizontal scale from the real scale such as the ship length if possible. It was regrettable that buoy data were not available (L154) because the information of incoming waves is quite important.
2) Selection of floe size
In section 3.1 they described “the minor axis length is the chosen floe length scale as it represents the characteristic break-up length scale” (L186-187). If they mean the ice break-up due to major propagating waves, the orientation of the minor axis should be aligned in the similar direction. But as far as looking at Fig. 4, the directions of the minor axis are variable. I guess various factors affected the ice break-up processes. I want the authors to explain what they meant by the characteristic break-up scale. Besides, I would like to know how the major axis length was determined and the relationship between the two parameters. I think this is important because the selection of floe size is relevant to the Area-based floe size distribution in Fig. 10.
3) Interpretation of break-up speed (Cb)
Based on the ratio of Cg to Cp (Fig. 11), they inferred that the break-up speed was controlled by the mass loading effect. Although it might be true, I am a bit skeptical about the idea. This approach would apply to the waves propagating in the fractured ice area. But I consider the ice break-up mechanism would be involved to determine the break-up speed, and the situation is not necessarily the same as the mass loading effect. Some additional effect such as ice fatigue, as discussed by Langhorne et al.(1998), or the heterogeneous properties of sea ice should be involved. If they consider the break-up mechanism is not so important, please add some explanation.
I think the description can be more concise, focusing on the essence of the new findings. Regarding the novel way of computing the FSD, it might be better to add some general explanations about how effectively it represents the physical properties of FSD compared with the traditional way. I am wondering why they focus on d_max although they use d_min for drawing the AFSD.
* (Abstract, L11) “.. thicker ice can attenuate wave less than thinner ice.”
Is that true? To my understanding, in the thicker ice situation of NBB, the wave attenuation was less because of the less ice rigidity caused by more brine volume fraction.
*(Introduction) I think the background of this study was well researched. But if you agree, please consider adding the following papers for the observational studies that directly relate the FSD (L38): Kohout, A.L., et al. (2016): In situ observations of wave-induced sea ice breakup.
Deep-Sea Research II, 131, 22-27.
And for the analysis of the resulting FSD and its possible connection to sea ice flexural rigidity (L86): Toyota et al. (2011): Size distribution and shape properties of relatively small sea-ice floes in the Antarctic marginal ice zone in late winter. Deep-Sea Research II, 58, 1182-1193.
*(Introduction, L55) Please add the definition of “WIMs”.
*(Section 3.2, L192) “The wave phase speed is then obtained..”
I am wondering that judging from the estimation method, this might correspond to the wave group velocity (Cg). It seems that they treated this value as the group velocity in section 5.2, didn’t they? To my understanding, the cruising ship generated the fixed frequency, which induced the waves with various two-dimensional wave numbers satisfying the dispersion relation. The observed large wave amplitude evolution corresponds to the maximum group velocity produced by them.
*(Section 4.2, L228) “.. the minor axis d since..”
I am wondering if the orientation of the minor axis might be important as well. I want to know how the length of the major axis was determined. Is that because of the heterogeneous properties of sea ice or any other reasons?
*(Section 5.1, L270-271) “The shape of the AFSD also highlights the fact that this process alone does not explain the power law distribution…”
This is interesting. To show it clearly, how about displaying the (traditional) cumulative FSD directly, if you agree?
*(L277) “propose” should be “proposed”.
*(Section 5.1, L319-320) “Toyota et al. (2011) to consider that..”
Since they introduced this idea to explain the threshold of two regimes, I feel that their concept is not inconsistent with the authors’ idea described in this paper.
*(Section 5.1, L350-354) Equation 14 & 15
According to the definition, it seems that β corresponds to the ratio of x* to wavelength. Please add some description about the physical meaning of β, which would facilitate the readers’ understanding.
*(Section 5.1, L367) “an” should be “and”.
*(Section 5.2, L406-408) “this result rather suggest that…”
This is an interesting result and I agree.
That is all.