The authors Rampal, Bouillon, Bergh, and Olason have revised their manuscript now entitled “Arctic sea ice diffusion from observed and simulated Lagrangian trajectories” significantly and with great success following the suggestions of the reviewers. This is now an excellent paper on sea ice drift, well structured, well written, and with a clear message. The study now focuses on sea ice diffusion with the application to pollutant dispersion. The model comparison of TOPAZ and neXtSIM, which previously was a concern shared by all reviewers, has been improved and its presentation has been reduced to a useful addition of the paper.
The paper is now in good shape to be accepted for publication in The Cryosphere. This said I list a number of suggestions, mostly regarding wording, but also some necessary corrections that the authors may want to consider before publication.
Important corrections/suggestions:
There are three references to the mean diffusivity of the sea ice cover (line 194, Fig. 3 and line 537), which I think should be consistent but currently read 1.0 x 103, 1.1 x 103 and 1.2 x 103. Same holds for the integral time scale mentioned in Figure 3 (see comment below).
Figure 6: I am not sure what “Nr. 119” etc. means. Is this the number of buoys/floats for each winter? If yes, then better use “N=119” referring to sample size and state this in the caption.
Figure 8: the x-axis label should read “mean speed”; fluctuating speed is shown in Figure 9.
Figures 8 and 9: I think the dashed line is the exponential fit and the dotted line depicts the Gaussian function. Currently the caption states the opposite. If I am right, just correct he captions of Figures 8 and 9. Otherwise, the statements in the main text are somehow wrong or hard to agree with.
It would be extremely helpful for the discussion in Chapter 3 if the authors would provide a contour plots of the ice thickness distribution of all three data sets. Since this is for Chapter 3 it should be an average of winters 2007-2010. For the TOPAZ and neXtSIM simulations this can easily be provided. For the observed ice thickness one could either check availability of satellite derived estimates or use the PIOMAS distribution (which the authors use to adjust their neXtSIM initialization). The maps could either be provided as additional panels within Figure 11 or as a separate Figure. Alternatively, a rough hint at the thickness distribution could be added to the existing maps in Figure 11 as black contours on top of the color patches, then maybe just roughly 1 to 3 m in 0.5m increments.
Wording throughout the paper:
Use “search area” and “search radius” instead of “searching area” and “searching radius”
Not sure what The Cryosphere guidelines say, but I think using parenthesis when referencing Equations is common: “Equation (1)” instead of “Equation 1”.
Comma usage with respect to variable names should be consistent throughout the paper, e.g. ‘variable, X …’ or ‘variable, X, … ‘ or ‘variable X …’; personally I prefer the latter.
Line by line suggestions:
line 3: “At the surface, …” otherwise the sentence implies accidents at the seafloor or at great depth but omits ship damage.
line 6: “random” or “chaotic” better than “unpredictable fluctuating”; otherwise correct to “unpredictably fluctuating”
lines 8-10: remove parentheses; add “Eulerian” to “… neXtSIM and the Eulerian coupled ice-ocean …” to stress this major difference of the two models; and remove “run on two different configurations”, because this is already implied (and details are given later).
18: “… may differ from or agree well with …”
19-20: “illustrates the usefulness of first applying a diffusion analysis … modeling systems that include … before using these …”
25ff: replace ‘render’: “…facilities may hamper access to the polluted area for several months (D. et. al., 2011). These conditions also make the detection…”
29ff: “… under the sea ice and, therefore may be transported by the ice over … (RC, 1997). In this context, improving the understanding of sea ice trajectories is crucial for risk assessment … in Arctic seas. Passive tracer modeling …”
51f: “mean (predictable)” and “fluctuating (unpredictable)”; additional information or definition should be given in parentheses
72: align Equation (3) with left text border
75: add ‘the’: “… term similar to the Coriolis term”
81: “Nevertheless, such properties have been used to reproduce …”; drop speculation about future use here
84: “Alternatively, the advection-diffusion equation (Eq. (1)) could be …”; add comma and reference
87: replace “/” with “or”: “simulated or observed”
91: “ … or defined such that it accounts for the unresolved …”
100: replace “Those” with “These”
105: “… winter conditons, as this season has been identified to be most critical for oil …”
114f: “… is done for two simulations obtained from two different models.” Different models implies possibility of diverting configurations; details are given later correctly.
132: consider to add a bold red outline to map in Figure 1 depicting the region described here. Then, add a reference to Fig. 1 to this sentence (after “80˚N”).
137: this sentence states an unfortunate limitation of the study as presently most of the Arctic Ocean is dominated by first-year ice (and will be in the future). Drastically said, it may render the numbers presented later in the study useless for future application by stakeholders. The authors need to discuss this issue more (in section 2.5) or/and refine the wording of this sentence.
141: “Before being published, however, the buoy positions …”
157: the bold line in Figure 2 depicting the mean should be drawn even thicker
162: “By repeating this for all the available buoys …”
171: “circle” instead of “cercle”
178 and 195f: Figure 3 only shows the example of L=400 km and T=165 days. It would be nice to see whether this choice is truly optimal. My first thought of adding more lines of other (L,T) pairs to Figure 3 is not optimal. I rather urge the authors to show Lambda as function of L,T in a new panel added to Figure 3, a contour plot. In line 195 you discuss a plateau that such a plot could potentially show and that would much help to trust he argument in lines 178 and 195.
193 Lambda=1.5 days does not match Lambda=1.4 given in Figure 3. These numbers should be consistent. (same for diffusivity K)
193/194: drop sentence “Note that the diffusivity …discussed in Section 2.3.” here and add a similar statement in Section 2.3 itself.
199: should this rather be C & T 1985 (instead of 1984) as in line 38? Also, please check if C&T ’84 is cited elsewhere (I think not), i.e. when changing this line remove the paper from the references list.
199: split sentence: “… mean circulation. This enables …”
203: “… properties of the medium by …”; use singular
212: remove “.” After Equation (3) as sentence is continued
214: ‘time much shorter’ sounds weird, better use “time periods shorter than” or “time much smaller than”; same for ‘time longer than’ in line 218
214: replace “we are” with “the particle is”
217: remove parentheses and replace ‘comes’ with ‘results’: “This simply results from …”
222: remove parentheses: “…, i.e. where fluctuating ….uncorrelated.”
224: I suggest to add statement about mean diffusivity presented in Figure 3 here: “For the example given in Figure 3 a mean diffusivity of 1.1 x 10^3 m^2s^-1 was computed.”
240 split sentence: “… integral time scale Lambda. With Lambda=1.4 days we find a time scale similar to the one …”
244: “… constant alpha), for which we find a good match.”
244-247: the statement about the work of Rampal et al. 2009 “whereas the magnitude presented … to the coming discussion.” does not belong here where new results are presented but should be moved to Section 2.5 Discussion instead. Same for lines 257-259 “Note that the value … in their study.”
256 Here, Table 2 is referenced before Table 1. Please switch order of Tables so that Table two becomes Table 1.
263: replace “a season” with “6 months”, which is close to 165 days and somewhat more precise than ‘a season’.
272: replace “values” with “magnitudes”
274: make this statement stronger by using “is a crucial” rather than “may be a crucial”
280: drop “We checked that” from beginning of sentence
284: rephrase and split this sentence: “For forecasts longer than a few days, typically only the mean ice drift can be trusted. Then, the long-term average standard deviation provided here could be used …”
286: “For example, the search area could be defined …”
290: should refer to Table 2 here after switching Table sequence.
294: replace “non-predictive” with “unpredictable” to be consistent
302: “… represented by a single mean value derived from these decades”
307: add ‘the’: “… of the two sea-ice(-ocean) modeling platforms…”
315: “However, as sea ice, especially compact pack ice, does not behave …”
319: remove ‘the’ from “used for the oceanic drifters”; and split sentence: “… (D. et . al. ’12). This approach consists of …”
340: replace “one” with “single”, i.e. “single-thickness-category sea ice model”
345: replace “run” with “used”
348: “… TOPAZ simulations analyzed in the following start on …”
349: replace “coming” with “extracted”
350: you may drop “free-run” here as this has been made clear above
350ff: the sentence sounds like wind is the only atmospheric forcing field applied but I guess there must also be temperature and possibly parameters for a radiation budget. Please rewrite to either “The applied wind forcing is the …” or state the other forcing fields as well.
353: “The TOPAZ model in free-run mode has been …”
356: split sentence: “… platform (not yet documented). The same value is also used here.”
357: “… in the free run is generally underestimated and has reduced horizontal gradients, i.e. shows too thin ice in areas of thick ice and too thick ice where the ice should be thin”; drop ‘inversely’
359: “… TOPAZ reanalysis, which applies assimilation of ???, but the total …” insert assimilated quantities (if too many, just say ‘applies assimilation’).
363 add comma: “…shelf sea, where …”
365: drop ‘here’ in “…model is here performed …”
365: “hourly sea ice velocity”: is this saved as hourly mean or snap shot? If saved as mean, say “hourly mean sea ice velocity”
371: “… similar results to computing the float positions during run-time with the advantage …”
378: “salinity. While still being under development, the model is already used in an experimental …”
388: add ‘reanalysis’ to “… TOPAZ reanalysis ice thickness …”
389ff: “… covered with ice. As the modeled ice volume of the TOPAZ reanalysis is known to be too low (S. et al., ’15), we increased … given by the PIOMAS model (Z & R, ’03) on September …”
395: “TOPAZ reanalysis”
400: Please add the temporal resolution of the ASR forcing. This is important when later discussing the lack inertial motions in the simulations.
404: “… May onwards (Rampal …)”
405 replace “look at” with “analyse”
407: really ‘no’ bias? I guess it is a very small bias, probably negligibly small, i.e. “… showing only a negligible bias in the 3-day drift…”; aslo drop “s” from “3-days”.
409: merge and shorten sentences: “… Eulerain fields due to the remashing techniques applied (see Rampal …”
415: drop ‘the’ and add ‘float’: “Figure 6 shows maps with all the buoy/float trajectories …”
416f: “… datasets. The three winter subsets from 2007 to 2010 are much … reference data set of 1979-2011 analysed in Section 2.1.”
432: I think from Figure 6 it is not very clear that neXtSIM is superior (except for the discussed thick ice area north of the CAA), the judgement seems subjective. I just suggest to add a note, which also helps to introduce the following analysis, such as: “Both models seem to have advantages and disadvantages and ice motion patterns may also be affected by the different wind forcing applied, thus a more objective measure of the quality of the ice velocity simulation is needed.”
433: remove “also”
434: add “more objectively.” to end of sentence after ‘…mean drift’.
437: add “(dashed line)” after ‘… an exponential function’. -> see also my main comment about likely mixed up explanation of dotted and dashed lines in captions of Figure 8 and 9.
438: “… follow an exponential distribution but has similarity to a Gaussian function (dotted line), and has a mean value …”
460: add “but are much closer to the Gaussian fit.” At end of sentence after ‘an exponential distribution’.
462: “… within the velocity range 0 to …”
464: remove “here”
468 the reference should be “(Table 1)” after switching the tables
478f: “… Archipelago (i.e. as small as about 0.3 x 10^3 m^2s^-1) and the larger values in the Beaufort and East Siberian seas (1.5 – 2.5 x 10^3 m^2s^-1).”; please check the magnitudes for the IABP data again, to me it looks like the minimum is rather around 0.2 – 0.3 than 0.5. And also add numbers for the larger values (I switched Bft. And East Sib. on purpose to because East Sib. has the larger magnitudes.
494 “(mean drift speed smaller than …)”
501f: “ocean model, which overestimates the size and misplaces the center of the Beaufort Gyre compared to …”
510: remove “well” after ‘represent’ and instead add “much better” at end of sentence.
512: “… are underestimated, however, just as in …”
514: “may thus originate from the oceanic forcing adapted from the TOPAZ reanalysis. Moreover, effects by using different wind forcing cannot be excluded as well.”
518f: add comment about temporal resolution of wind forcing not sufficient to excite inertial motions. To trigger inertial motions forcing time step must be smaller than 1h.
528: “… integral time scale. This may allow to maintain the good performance …”
533-535: shorten: “… and we confirm the results of Rampal et al. (2009b) that the appropriate … and 165 days. We additionally verify …”
536: numbers given should be consistent with Figure 3 and associated discussion in main text.
540: add explanation for meaning of 3 std. dev.: “… to 3 standard deviations of the fluctuating displacement, which would include the polluted area with 99% confidence, we find that… ” This is meant for stakeholders who may want to apply your numbers.
553: “… sea ice model output before using it for …”; use singular instead of plural
568: “exponential distribution – like the observations – an reproduce …”
582: “… (mean circulation of the atmosphere and ocean, spatial … “
584: replace “whose the respective roles” with “which” |
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