the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Evolution of turbulent kinetic energy during the entire sandstorm process
- Center for Particle-laden Turbulence, Lanzhou University, Lanzhou 730000, PR China
- Center for Particle-laden Turbulence, Lanzhou University, Lanzhou 730000, PR China
Abstract. An adaptive segmented stationary method for non-stationary signal is proposed to reveal the turbulent kinetic energy evolution during the entire sandstorm process observed at the Qingtu Lake Observation Array. Sandstorm which is a common natural disaster is mechanically characterized by a particle-laden two-phase flow experiencing wall turbulence, with an extremely high Reynolds number and significant turbulent kinetic energy. Turbulence energy transfer is important to the understanding of sandstorm dynamics. This study indicates that large-/very-large-scale coherent structures originally exist in the rising stage of sandstorms with a streamwise kinetic energy of 75 % rather than gradually forming. In addition to carrying a substantial portion of energy, the very-large-scale-motions are active structures with strong nonlinear energy transfer. These structures gain energy from strong nonlinear interaction. As sandstorm evolves, these large structures are gradually broken by quadratic phase coupling, with the energy fraction reducing to 40 % in the declining stage. The nonlinear process in the steady and declining stages weakens and maintains a balanced budget of energy. The systematic bispectrum results provide a new perspective for further insight of sandstorms.
Hongyou Liu et al.
Status: final response (author comments only)
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RC1: 'Comment on acp-2021-889', Anonymous Referee #1, 01 Dec 2021
The authors investigated the entire sandstorm process (including the rising stage, the steady stage and the declining stage) to reveal the turbulent kinetic energy evolution. They proposed an adaptive segmented stationary method to separate the wind velocity series of a sandstrom. On this basis, the pre-multiplied spectra and bispectrum were analyzed during the sandstrom. The results indicate that the LSMs/VLSMs are active structures with strong nonlinear interactions and increase the wind velocity in the rising stage. As sandstrom evolves, these large structures are gradually broken by quadratic phase coupling and the energy fraction of VLSMs is the smallest in the declining stage. The systematic bispectrum results provide a new perspective for further insight of sandstroms. The authors collected dependent data, chosen suitable model, and tested it fully. The conclusion is reliable and suggestive. I am very impressed by the study, and approve the manuscript to be accepted as is.
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AC1: 'Reply on RC1', Hongyou Liu, 01 Dec 2021
The authors would like to express their sincere gratitude to the reviewer for the comments. Your recognition of the present work is a great encouragement to the authors. We hope to generate more important and novel results through continuous efforts in the future. Thank you very much for all your help.
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AC1: 'Reply on RC1', Hongyou Liu, 01 Dec 2021
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RC2: 'Comment on acp-2021-889 by Liu et al.', Hosein Foroutan, 17 Mar 2022
In this paper, Liu et al. investigated the turbulence structures and scales evolving during the rising, steady-state, and declining stage of a sandstorm. Investigation of a real sandstorm through a lens of wall-bounded turbulent flow dynamics is interesting and meritorious. However, in my opinion, a number of major issues need to be addressed before publication.
General Comments
1. The paper fails to investigate local meteorological and synoptic conditions associated with the case of the sandstorm studied herein. This investigation is crucial as weather features are expected to directly impact large and very large-scale motions (LSMs and VLSMs) of turbulence. Specifically:
1.1. The sandstorm event studied here must be described in details in Section 2.1, including the date/time, weather conditions, potential meteorological drivers, etc (see for example Gasch et al., 2017). Without this information, all the discussion of results regarding the onset of the sandstorm and the link between LSMs/VLSMs and synoptic conditions is questionable.
1.2. Throughout the text, authors referred to the study by He at al. (2020) to describe the physics and meteorological drivers of a sandstorm. This is problematic, because He et al. (2020) investigated a mesoscale convective dust storm generated by cold pool outflow (AKA haboob), which is drastically different that a synoptic-scale dust storm. (see Knippertz (2014) for more information). More concerning is that the paper describes ‘synoptic events’ and ‘cold front’ in a sandstorm on the basis of the study of He et al. (2020), who looked into a haboob sandstorm.
2. The structure of the paper should be improved. Specifically:
2.1. The paper should be shortened:
- Remove Figure 3 or move it to a supplementary information document as it is simply a repetition of the text (lines 162-174).
- Figure 4 and the discussion around it (lines 175 -192) seems to be out of place and should be moved to a supplementary information document.
- The spectral method (section 3) is a well-established approach in the study of turbulence, and the contribution of this work in terms of methodology development is not clear. Therefore, I suggest this section to be shortened and the text to be moved to a supplementary document.
2.2. Lines 198 to 213 should be presented earlier in the paper together with the discussion around Figure 2.
Specific Comments
- The segmentation method described in figure 3, involves a number of subjective criteria including the IST threshold (30%), the time window used for initial time-averaging (1 hr), and dt (5 min). The uncertainty of these choices in final results should be studied and discussed. Specifically, after applying the data processing procedure the size of all segments ended up being very close to or exactly 1-hr which was the initial choice for time-averaging and removing the time-varying mean. One may ask whether the 1-hr initial choice could basically govern the whole procedure and making the entire segmentation algorithm irrelevant. A sensitivity test should help answering this question.
- Figure 2(a): Can authors comment why the time-varying average velocity obtained by the EMD method contains low frequency fluctuations in the rising stage, which are absent in the other two methods (moving windows and adaptive wavelet transform)?
- The studies of Kim and Adrian (1999), Guala et al. (2006), and Balakumar and Adrian (2007) have been referred to throughout the text to describe and identify LSMs/VLSMs. All these studies investigated turbulent channel and pipe flows (internal), rather than a true turbulent boundary layer flow as relevant to a sandstorm (external). Monty et al. (2009) concluded that VSLMs in boundary layers are different from those in channel and pipe flows (e.g., as in Kim and Adrian (1999)). Therefore, there is a concern in using results/criteria from internal flows in the case of a sandstorm with very high Reynolds number.
- Figure 6: What is the difference between subfigures (a) and (b) , (c) and (d), (e) and (f) ? It was neither mentioned in the caption nor discussed in the main text.
- Figure 7(b) and lines 330-333: The sharp decreases in the declining stage were attributed to the exhaustion of energy at this stage, but why there is a maximum right when the declining stage is started and before this sharp decrease?
- Figure 8: The two fraction numbers contributed by VLSMs of 75% and 40% reported throughout the text were obtained from this figure. As this fraction is changing with height, it is crucial that either the location where the fraction is reported be mentioned everywhere in the text or an average value below a certain height be reported. It seems that the two reported fraction values (75% and 40%) are simply the limit of measurements in terms of height.
- The Taylor’s hypothesis of frozen turbulence has been used throughout the text. Does the level of turbulence intensity (i.e., fluctuations compared to the mean wind value) justify this approximation?
- Figure 11 and the text around it: How are the “small-scale motions” defined? (This point may be linked to point 3 above questioning the criteria to define VLSMs).
- Figure 11: Including an inset in (b) and (c) are quite confusing. I think the plots for all the heights can be presented as the main figure instead of being included as an inset.
- Line 481-486: This statement seems to be an overgeneralization of the lifetime of a sandstorm based on observations of a single event (This point is directly linked to my first point under general comments).
- The data provided in the Zenodo data repository has no metadata, data header, or any information to help using this data.
Technical Comments
- Line 14: check for grammar correction
- Line 19: use “humidity” instead of “dampness”
- Line 24: “A kind of power”: sounds awkward
- Line 27: “… impact on sandstorm more intensively, significantly, contributively than other…” : sounds awkward
- Line 49 and throughout the text: use “transport” instead of “transportation”
- Line 85: “necessary”: Do you mean “ideal” or “suitable” ?
- Throughout the text: I suggest using “surface” instead of “wall”. I understand that “wall-bounded turbulence” is an established term, but the word “surface” or “ground” seems to better suit an atmospheric application.
References
Gasch, P., Rieger, D., Walter, C., Khain, P., Levi, Y., Knippertz, P. and Vogel, B., 2017. Revealing the meteorological drivers of the September 2015 severe dust event in the Eastern Mediterranean. Atmospheric Chemistry and Physics, 17(22), pp.13573-13604.
He, Y., Gu, Z., Shui, Q., Liu, B., Lu, W., Zhang, R., Zhang, D. and Yu, C.W., 2020. RANS simulation of local strong sandstorms induced by a cold pool with vorticity. Atmosphere, 11(4), p.321.
Knippertz, P., 2014. Meteorological aspects of dust storms. In Mineral dust (pp. 121-147). Springer, Dordrecht.
Monty, J.P., Hutchins, N., Ng, H.C.H., Marusic, I. and Chong, M.S., 2009. A comparison of turbulent pipe, channel and boundary layer flows. Journal of Fluid Mechanics, 632, pp.431-442.
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AC2: 'Reply on RC2', Hongyou Liu, 13 Apr 2022
Dear reviewer,
The authors would like to express their sincere gratitude to the reviewer for the comments. These comments are all valuable and helpful for improving our manuscript. Every comment or suggestion was checked very carefully. Based on these comments, we revised the manuscript thoroughly and seriously, which we hope could meet with approval. Point-by-point replies and corresponding modifications are provided in the supplement: “Response to Referee 2”.
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EC1: 'Comment on acp-2021-889', Peter Haynes, 21 Mar 2022
You will see that a second referee has now posted a comment on your paper. As responsible Editor I regret the time that it has taken to find a second referee (and I am very grateful to the referee who agreed for providing their report promptly).
Please now consider the two referees' reports together and provide a revised version of the paper + responses to referees.
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AC3: 'Reply on EC1', Hongyou Liu, 13 Apr 2022
Dear Editor,
Thank you very much for your attention and the comments from the referees about our manuscript entitled “Evolution of turbulent kinetic energy during the entire sandstorm process” (acp-2021-889), submitted for publication in Atmospheric Chemistry and Physics.
We have carefully considered all comments from the referees during the preparation of the present revised version of the manuscript. Changes in the revised manuscript are marked in blue. Point-by-point replies to the referee 2 are provided in the “Response to Referee 2”.
We sincerely hope this manuscript will be finally acceptable to be published in Atmospheric Chemistry and Physics. Thank you very much for all your help and looking forward to hearing from you in due course.
Best regards
Yours sincerely,
Dr. Xiaojing Zheng (Professor)
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AC3: 'Reply on EC1', Hongyou Liu, 13 Apr 2022
Hongyou Liu et al.
Data sets
Evolution of turbulent kinetic energy during the entire sandstorm process Hongyou Liu; Yanxiong Shi; Xiaojing Zheng https://zenodo.org/record/5184882
Hongyou Liu et al.
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