the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Sub-surface processes and heat fluxes at coarse-blocky Murtèl rock glacier (Engadine, eastern Swiss Alps)
Abstract. We estimate the sub-surface energy budget and heat fluxes in the coarse-blocky active layer (AL) of the Murtèl rock glacier, a seasonally snow-covered permafrost landform located in the eastern Swiss Alps. In the highly permeable AL, conductive/diffusive heat transfer including thermal radiation, non-conductive heat transfer by air circulation (convection), and heat storage changes from seasonal accretion and melting of ground ice shape the ground thermal regime. We quantify individual heat fluxes based on a novel in-situ sensor array in the AL and direct observations of the ground ice melt in the years 2020–2022. Two thaw-season mechanisms render Murtèl rock glacier comparatively climate-resilient. First, the AL intercepts ~70 % (55–85 MJ m−2) of the thaw-season ground heat flux by melting ground ice that runs off as meltwater, ~20 % (10–20 MJ m−2) is spent on heating the blocks, and only ~10 % (7–13 MJ m−2) is transferred into the permafrost body beneath and causes slow permafrost degradation. Second, the effective thermal conductivity in the ventilated AL increases from 1.2 W m−1 K−1 under strongly stable temperature gradients to episodically over 10 W m−1 K−1 under unstable temperature gradients, favouring convective cooling by buoyancy-driven Rayleigh ventilation (thermal semiconductor effect). In winter, radiatively cooled air infiltrating through a discontinuous, semi-closed snowcover leads to strong AL cooling. The two characteristic parameters (effective thermal conductivity and intrinsic permeability) are sensitive to debris texture, hence these convective undercooling processes are specific to highly permeable coarse-blocky material.
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RC1: 'Comment on egusphere-2024-172', Anonymous Referee #1, 17 May 2024
GENERAL COMMENTS
The manuscript presents the unique data set collected in a rock glacier using innovative approaches. I am not aware of similar data set collected anywhere in the world, and I believe that the study has a tremendous potential to make a highly unique and significant contribution to the scientific understanding of rock glaciers. The authors are commended for collecting this highly valuable data in a challenging environment. Unfortunately, however, the manuscript is poorly developed and hard to comprehend. The English language is grammatically correct, but it is impenetrable in many places due to the overloading of information. The manuscript seems to have more than 14,000 words in the main part, excluding the reference list and appendix. This is excessively long compared to a standard length of contemporary research articles (e.g., 8000-8500 words). I feel that the manuscript was submitted prematurely and could have been made much more interesting and useful. Instead of bombarding the reader with all the data the authors have observed, they could select those data that are essential and most interesting, and develop a coherent story around those data. For example, the authors could use their own abstract as a guidance in the process of selecting the data and writing a concise and well-developed manuscript. Personally, I find the data presented in Figures 7, 10, 13, and 14 most interesting. In the following, I will make specific comments and suggestions on the contents of the current manuscript, but the authors can ignore my suggestion if a particular content is dropped in a new manuscript.
SPECIFIC COMMENTS
Line 75. This statement is not consistent with commonly accepted definition of REV, which should have a statistically meaningful number of pores to be able to define REV-scale variables such as porosity and mean pore size. Please redefine the REV for this study.
Line 350. It will be useful to report the maximum (i.e. peak) snowcover thickness and date here, so the reader can get a sense of the winter condition.
Line 355. The surface meteorological conditions are described in another paper, but they need to be briefly presented in this paper for the reader, who may not have time to read the second paper. For example, I suggest that the authors add another panel showing daily mean temperature and weekly (or monthly) precipitation.
Line 357. Please add ‘(Eq. 4)’ after the Rayleigh-Darcy numbers.
Figurer 6a. Please include the legends for Ra = 27 and 40 in the graph instead of explaining them in the figure caption. The former is much easier for the reader than the latter.
Line 359. Please explain the critical Ra in the main texts, not in the figure caption.
Line 361. To help the reader understand this sentence more easily, it will be useful to present Figures 5 and 6 together, along with another panel showing air temperature and precipitation, and possibly snow depth.
Figure 6b-6d. In this graphs, the highest point is air temperature. It is not appropriate to connect the air temperature point with the first subsurface temperature point by a straight line, because the temperature profile in the boundary layer is not linear. Please come up with another way of demonstrating the data.
Figure 6b. These graphs are difficult to comprehend. For example, there are two red lines for 2022 but no explanation is given. Also, no explanation is given in the caption for Ts. Please improve the presentation of these graphs.
Line 368. Table 3 needs to be shown together with Figures 6b-6d so the reader can easily understand the setting of each line. I suggest that Figure 6a be presented as a panel in Figure 5, and Figures 6b-6d be presented together with Table 3.
Line 372. Dec-Mar. This is shown as Dec-Apr in the figure legend. Please be consistent. Each occurrence of inconsistent information detracts the reader’s thought process and makes the texts more difficult to follow.
Line 375-376. I do not see ‘striking asymmetry’ in Figure 6b. The data indicated by circle-2 seems to show the same deviation for both high and low sides. Please clarify.
Line 380. To demonstrate ‘close to saturation’, it is much better to show relative humidity. Unless the authors intend to use specific humidity to estimate vapour flux, please use relative humidity in this graph.
Line 399. This is only for the spring of 2021. Please clarify that.
Line 400. ‘Inferred from’. This is not clear. Please explain it.
Line 440. I find this section interesting. Please consider focusing on this section and deleting or condensing other less interesting sections.
Line 470. This section is also interesting.
Line 480. The sub-section on temperature index model seems less relevant and interesting than the previous sections.
Line 475 and 483. Please use a consistent symbol for the derivative of zeta. If the dot notation is used, please define the symbol at its first occurrence.
Line 506. This sub-section is interesting as well.
Line 507. ‘denoted by the summation symbol’. I do not see the summation symbol in Figure 14. Please use a consistent notation.
Line 508. The AL exits the zero-curtain phase. Where in Figure 14 is this indicated? Please explain.
Line 509. The thermodynamic reference level in Figure 14. Where in the figure is this indicated? Please explain.
Line 509. The symbol for sensible heat in this sentence is slightly different from the one appearing in the figure. Please use a consistent symbol.
Figure 14. Please spell out SEB in the figure caption, so the reader can remember what this was.
Citation: https://doi.org/10.5194/egusphere-2024-172-RC1 - RC2: 'Comment on egusphere-2024-172', Benjamin Hills, 02 Oct 2024
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EC1: 'AE Comment on egusphere-2024-172', Jens Turowski, 04 Oct 2024
Dear authors,
apologies for taking so long to deliver the reviews; for some reason, it was exceptionally difficult to find referees. I nominated more than 50!
In any case, we have two reviews now. Both reviewers highlight the quality and uniqueness of the data, but criticize the organization and presentation of the material. Reviewer #2, in particular, gives specific pointers to how you could approach revisions.
I am looking forward to reading a revised version of the manuscript.
All the best, Jens Turowski
Citation: https://doi.org/10.5194/egusphere-2024-172-EC1
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