Effects of 3D electric field on saltation during dust storms: an observational and numerical study

Zhang, Huan; Zhou, You-He

doi:https://doi.org/10.5194/acp-20-14801-2020

Articles | Volume 20, issue 23

https://doi.org/10.5194/acp-20-14801-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-20-14801-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 20, issue 23

Research article

|

02 Dec 2020

Research article |

| 02 Dec 2020

Effects of 3D electric field on saltation during dust storms: an observational and numerical study

Huan Zhang and You-He Zhou

Download

Final revised paper (published on 02 Dec 2020)
Supplement to the final revised paper
Preprint (discussion started on 06 Aug 2019)
Supplement to the preprint

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

- Printer-friendly version

- Supplement

RC1: 'Comments on acp-2019-439', Anonymous Referee #1, 29 Aug 2019
- AC1: 'Authors' response to Referee #1', Huan Zhang, 13 Nov 2019
RC2: 'Review comments', Anonymous Referee #2, 02 Sep 2019
- AC2: 'Authors' response to Referee #2', Huan Zhang, 13 Nov 2019

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Huan Zhang on behalf of the Authors (13 Nov 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (29 Mar 2020) by Ulrich Pöschl

RR by Anonymous Referee #3 (04 Apr 2020)

Suggestions for revision or reasons for rejection

I think there are some major problems in the paper, which suggest that the main ideas and conclusions may be incorrect. Furthermore, I don't think the reviewer responses really addressed the previous reviewer comments -- the responses were so long and strayed from the point, rather than clearly and effectively focusing on the concern.

1. The authors continually say throughout the paper that previous 1d electric fields found reduction in saltation mass. This is not true. Kok Renno 2008, as well as other papers, predicted/found enhancement of saltation with 1d electric fields. This is a major problem.

2. A previous reviewer brought up a very important point, and the authors do not give a convincing answer. The reviewer says "However, the manuscript does not explain why streamwise E-field and spanwise E-field happens, and why are they an order of magnitude larger than the vertical electric field?"
- the answer the authors give is vague hand waving, and does not convince me. There is a physical justification for electric field in the vertical direction -- charge depending on particle size, and height of particles depending on particle size -- thus charge depends on height giving an electric field. But there is no physical justification for systematic streamwise or spanwise fields (that I'm aware of), other than random fluctuations
- in my opinion, this finding suggests that perhaps the results are simply incorrect and unreliable, and that the paper should not be published as it would be very misleading. It is incumbent on the reviewers to demonstrate that their results are correct, both in terms of the measurement and the physically reasonable basis.

3. The authors argue that the effects of mid-air particle-particle collisions are significant. I'm surprised by this, since the density of particles in the air is low, but perhaps they might be right. The authors should justify this claim is reasonable with a simple and easy-to-follow analysis, where they find the mean free path between collisions of the particles, which can be easily done in the same way its done for gases in physical chemistry textbooks. How does the mean-free path compare with the distance traveled during a saltation hop, and how many collisions would be expected per hop?

Hide

RR by Anonymous Referee #1 (11 Apr 2020)

RR by Anonymous Referee #4 (11 Apr 2020)

RR by Anonymous Referee #2 (14 Apr 2020)

Suggestions for revision or reasons for rejection

1. The authors stated in the introduction that the E-field effects on lifting and transport have been studied, which is followed by saying the effects on saltation remain obscure. Saltation is also a transport process. Please revise the statement to clarify what aspects of transport have been studied.
2. In the revised MS, both discrete wavelet transform (DWT) and the ensemble empirical mode decomposition (EEMD) are used to estimate the time-varying mean E-field. The authors used the 10th order approximation component of DWT that reflects an average timescale of 2e10 s and the last four EEMD components with a maximum mean frequency of 5.78e-2 Hz to reach the conclusion that both methods can capture the time-varying mean over a timescale of 17 minutes. However, 5.78e-2 Hz equals to ~ 17.3 seconds. Therefore the two methods should have captured different features but interestingly results seemed to agree. Does it mean that the dust storm actually was more stationary than expected at least in the timescale range of 17 s - 17 min?
3. The authors used >= 0.5 for the restitution coefficient in the analysis. Would you please provide reasoning for excluding the <0.5 range? Is there a known range of en for sand particles?
4. In the revised MS, the dimensionless variables are denoted with a superscripted '+'. This can cause confusion, especially when talking about E-field. I would suggest to follow the usual custom by using '*' instead.
5. How is the steady period of the observed dust storm defined? Also please be consistent with either 'steady' or 'stationary' period when referring to the shaded area in Fig. 4.
6. Some editing and grammatical suggestions (incomplete): P2: line22, remove 'truly'; line24, remove 'will'; line29, an ubiquitous. P3: line4, its direction reversed. P11: line1, is altered. P20line1 & P21line 24 dependent on...P24: line9, is effective to...

Hide

ED: Reconsider after major revisions (24 Apr 2020) by Ulrich Pöschl

AR by Huan Zhang on behalf of the Authors (03 Jun 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (18 Jun 2020) by Ulrich Pöschl

RR by Anonymous Referee #3 (22 Jun 2020)

RR by Anonymous Referee #4 (30 Jun 2020)

Suggestions for revision or reasons for rejection

The author’s responses of the review are long and in detailed. However, there are still some problems remaining:
According to the revised manuscript and the response of the review, the author expected the 3D electric field is produced by the very large turbulence structure, based on the idea of the volcanic eruption experiment of Cimarelli (2013). However, the size of particles in Cimarelli’s experiment is binary distribution, and move in the vertical direction, while in the simulation of this paper, the size distribution of sand is continuous distribution based on field observation, and move horizontal, is the pattern of movement still the same as that of Cimarelli’s experiments? In my opinion, the large particles are more likely to distribute near the ground due to gravity, and small particles disperse in the air, so that the vertical electric field should be much larger than horizontal electric field.
The author explained that large-scale and super large-scale turbulent structures are the reasons for formation of the horizontal electric field. While the size of large-scale or the super large-scale structures should be several ten meters or hundred meters, which is much larger than the scale of the experiment (below 1m) in the manuscript.
The author declared it is a 3D simulation, but the width of the domain in the manuscript is only 0.1 meters, which is much smaller than vertical scale, which should be considered as a 2D model.
The author indicated the mean mass-charge ratio is independent with the particle size distribution. However, the author calculated the charge based on the charge separation model, in which the amount charge transferred is calculated by the different contact surfaces. So, the mass charge ratio should be affected by the particle size distribution.
The number of Eq. 28 (line 18 in page 19) is wrong, which should be 29.
The author was wrong in response of question 10): below 0.01m, we can see from the Fig .10, mean velocity <up>, case 1<case 2≈case 3, not case 3 ≤case 2≤case 1, so we cannot conclude the value of mas flux: case2< case 1<case3, it should be case 1<case 2 < case 3.
In section of 3.5, the author made a wrong cite, which there is no definition of mean charge to mass ratio in the papers of Carneiro et al., 2013 and Dupont et al., 2013. Actually, the unit of mean charge to mass ratio should be C/kg, while in the formula(28d), the author considered it as m*C/s, which is not suitable in basic physic meaning.
In the supplement file, the PSD of particles was plotted in Figure S1, in which the mean particle size is around 100um. The author chose 100uC/kg as the mean charge to mass ratio, as well as considered the mean charge of one particle with 1.64×10‐12, which are contradictory. The mean charge of one particle should be calculated as Q=charge mass to ratio*Mass of particle = 100uC/kg*4/3π*(10-4)3 ≈ (10)-16, which is not agree well with the value of charge to mass in the paper of Merrison (2013).
In page 23, the author wrote the charge density effects the magnitude of transferred charges a lot when the charge density is low, which is easily to make a misunderstand. First, the author needs to clarify the reason why different particles have different capacity on unit surface. Actually, this character ρ_0 should not be called the charge density of particles. The author used it as the maximum capacity of charge on each unit surface on particles. The charge density should be calculated by the total charge divided by the particle surface. ρ_0 should be a constant value, which should be only decide by the material of the particles. The reason why when ρ_0 is over 1018, the mean charge to mass ratio getting stable is the product of ρ_i S_i-ρ_j S_j is getting same value. ρ_0 is not the main decision role anymore in the calculating this formula.
In Figure 5, the author showed the details about the electric field value varies with time. There is an interesting phenomenon that the magnitude of spanwise electric field and streamwise electric field are almost the same, and the vertical electric field oppositely varies in trend comparing to them. The author didn’t explain the reason of this phenomenon. If the author considers the spanwise and horizontal electric field are caused by the structure of turbulence, why does the magnitude and variation of spanwise electric field and streamwise electric field are almost the same? In fact, the turbulence structures in spanwise and streamwise should be different.
In the manuscript, the results show that the horizontal electric field is much stronger than the vertical electric field, which indicate particles will have strong spanwise motions, which seem not consistent with the real situation. The author could compare the magnitudes of the horizontal electric force and drag force.

Referee Report: PDF

Hide

ED: Reconsider after major revisions (07 Jul 2020) by Ulrich Pöschl

AR by Huan Zhang on behalf of the Authors (15 Jul 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (14 Aug 2020) by Ulrich Pöschl

RR by Anonymous Referee #4 (24 Aug 2020)

Suggestions for revision or reasons for rejection

There are some basic scientific questions that conflicted in the manuscript, and the author’s responses to the last review are not clearly and cannot be fully accepted.
The first response from author is not carefully expressed, and not enough investigation for the research background. The viewpoint that the triboelectric charging in a granular system is generally size-dependent is right, although different researchers have different views. Some researchers claimed that large particles tend to charge positively while smaller particles tend to charge negatively (the author make a mistake writing in the response), and other researchers claimed that small particles tend to charge positively while larger particles tend to charge positively (Mehrani and Grace,2005; Sowinski et al.,2010) .
The author claimed that the horizontal electric field is caused by the un-uniformly distributed fine particles, and the fine particles are more sensitive to the turbulent structure. But in this study, the author cannot explain from the simulation that the turbulent has effect on the small particle distribution, for the wind field in the simulation is a horizontally uniformed one. And due to the un-uniformed distribution of fine particles, the electric field in vertical or the horizontal from the large scale is much stronger cannot clearly shown yet.
The author didn’t reply directly to the second review question. The author said the large-scale and super large-scale turbulent structures are the reasons for formation of the horizontal electric field, but actually the field measurement was below 1m height. So why does the horizontal electric field is still produced under such a small-scale field?
I know what the author mean for the 3D, but I think it is better to point out that the simulation is a 3D-DEM model rather than a 3D model, since it is a horizontal uniformed case.
In the response, the author considered if the difference between two velocity value is less than 5%, then the values are almost the same. But for the mass concentration of case 2 and case1, the difference is also less than 5%, and the author didn’t consider it.
The updated fig. 5 shows the electric fields in different height. However, the horizontal E-fields are not always much larger than the vertical ones. It is height dependent. Thus, the author should point out it in his manuscript.
The author added that “ the man-made 1-D E-field may enhance sand transport in pure saltation”. However, the 3D E-field introduced in this simulation work is also man-made, not self-produced by the charged particles. Thus, the difference between previous works and this work is just the direction of the E-field, which is easy to know the effects on the transport rate. Addition, I think the horizontal electric force do have significant impact on the trajectory since the transport rate is affected mainly by vertical electric field, and the horizontal electric field is even larger than the vertical one.
In the description of Fig. 7 (line 14-15, page 46), better as “ are estimated from Zheng et al (2003)”.
In all, this manuscript is not suggested to publish before the revise.

Hide

ED: Reconsider after major revisions (24 Aug 2020) by Ulrich Pöschl

AR by Huan Zhang on behalf of the Authors (05 Oct 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (09 Oct 2020) by Ulrich Pöschl

RR by Anonymous Referee #4 (25 Oct 2020)

ED: Publish as is (25 Oct 2020) by Ulrich Pöschl

AR by Huan Zhang on behalf of the Authors (26 Oct 2020) Author's response Manuscript

Download

Article (7159 KB)
Full-text XML

Short summary

We assess the effects of triboelectric charging on wind-blown sand via observations and a numerical model. The 3D electric field within a few centimetres of the ground is characterized for the first time. By using the discrete element method together with the particle-charging model, we explicitly account for the particle–particle charging during collisions. We find that triboelectric charging could enhance the total mass flux and saltation height by up to 20 % and 15 %, respectively.