Technical note: Evolution of convective boundary layer height estimated by Ka-band continuous millimeter wave radar at Wuhan in central China

Zhang, Zirui; Huang, Kaiming; Yi, Fan; Liu, Fuchao; Zhang, Jian; Jia, Yue

doi:https://doi.org/10.5194/egusphere-2024-933

Preprints

https://doi.org/10.5194/egusphere-2024-933

Preprints

02 May 2024

| 02 May 2024

Technical note: Evolution of convective boundary layer height estimated by Ka-band continuous millimeter wave radar at Wuhan in central China

Zirui Zhang, Kaiming Huang, Fan Yi, Fuchao Liu, Jian Zhang, and Yue Jia

Abstract. Using the vertical velocity (VV) observed by a Ka-band millimeter wave cloud radar (MMCR) at Wuhan, we investigate the evolution of convective boundary layer height (CBLH) based on a specified threshold of VV variance. Compared with the CBLH retrieved from the lidar range corrected signal (RCS), the MMCR-derived CBLH exhibits lower values for a few hours post-sunrise and pre-sunset, but outside these two periods, they are generally in good agreement. Relative to the lidar RCS that is susceptible to the historical aerosol mixing processes, the CBLH estimated from the MMCR VV variance shows a rapid response to thick clouds and a less contamination by aerosol residual layer and long-distance transport of sand and dust, thus the MMCR VV observation can capture the CBLH evolution very well. The MMCR observation in 2020 depicts the seasonal and monthly variations in the CBLH. The seasonal mean CBLH reaches the peak heights of 1.29 km in summer, 1.14 km in spring, and 0.6 km in autumn and winter, with occurrence time between 13:30 and 15:00 LT. The maximum (mean) value of mean (daily maximum) CBLH rises steadily from 0.66 (0.87) km in January to 1.47 (1.76) km July, followed by a gradual decline to 0.42 (0.5) km in December. Statistical standard deviations are monthly-dependent, indicating the significant influence of weather conditions on the CBLH. This study improves our understanding of the Ka-band MMCR’s capability to monitor the CBLH, emphasizing its utility in tracking the dynamical processes in the boundary layer.

Received: 28 Mar 2024 – Discussion started: 02 May 2024

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20 Mar 2025

Technical note: Evolution of convective boundary layer height estimated by Ka-band continuous millimeter wave radar at Wuhan in central China

Zirui Zhang, Kaiming Huang, Fan Yi, Wei Cheng, Fuchao Liu, Jian Zhang, and Yue Jia

Atmos. Chem. Phys., 25, 3347–3361, https://doi.org/10.5194/acp-25-3347-2025,https://doi.org/10.5194/acp-25-3347-2025, 2025

Short summary

Zirui Zhang, Kaiming Huang, Fan Yi, Fuchao Liu, Jian Zhang, and Yue Jia

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2024-933', Andrea Burgos Cuevas, 10 Jun 2024

The manuscript is valuable and I do think that it should be accepted. However, there are major corrections that I consider that have to be made and they are specified in the attached document.

Citation: https://doi.org/10.5194/egusphere-2024-933-RC1
- AC1: 'Reply on RC1', Kaiming Huang, 27 Oct 2024
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-933/egusphere-2024-933-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-933-AC1
RC2:
'Comment on egusphere-2024-933', Anonymous Referee #2, 24 Sep 2024

See the attachment for my review, please.

Citation: https://doi.org/10.5194/egusphere-2024-933-RC2
- AC2: 'Reply on RC2', Kaiming Huang, 27 Oct 2024
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-933/egusphere-2024-933-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-933-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2024-933', Andrea Burgos Cuevas, 10 Jun 2024

The manuscript is valuable and I do think that it should be accepted. However, there are major corrections that I consider that have to be made and they are specified in the attached document.

Citation: https://doi.org/10.5194/egusphere-2024-933-RC1
- AC1: 'Reply on RC1', Kaiming Huang, 27 Oct 2024
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-933/egusphere-2024-933-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-933-AC1
RC2:
'Comment on egusphere-2024-933', Anonymous Referee #2, 24 Sep 2024

See the attachment for my review, please.

Citation: https://doi.org/10.5194/egusphere-2024-933-RC2
- AC2: 'Reply on RC2', Kaiming Huang, 27 Oct 2024
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-933/egusphere-2024-933-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-933-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Kaiming Huang on behalf of the Authors (27 Oct 2024) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (18 Nov 2024) by Geraint Vaughan

RR by Anonymous Referee #2 (04 Dec 2024)

RR by Anonymous Referee #1 (16 Dec 2024)

Suggestions for revision or reasons for rejection

Dear editorial committee and dear authors:
The majority of the general comments I had in the manuscript are roughly resolved in the revised version. However, there are still some important features that need to be further explained or more precisely presented.
On my former first general comment where I pointed out that the focus and aim of the paper should be more clear, authors mention that it is addressed in the last paragraph of section 1; and it is more explained there, but still a further explanation is necessary. When they say "algorithms" in line 122. There are algorithms based on thermodynamic characteristics (i.e. profiles of temperature and/or humidity), on dynamic characteristics (wind, turbulence) and on backscatter. A review of these different methodologies can be found in Kotthaus et al. (2023) (https://doi.org/10.5194/amt-16-433-2023). The algorithm utilized by the authors is clearly a dynamical one but that should be clearly stated and the capabilities and limitations that this approach has needs to be considered. Moreover it is compared with the RCS which as far as I understand is a backscatter-based algorithm. All this should be clearly assessed while the authors compare their methodologies.
The introduction is less repetitive and better structured as was asked by me, however still some asseverations should be more precisely stated, such as the ones pointed out in lines 66 and 80 (please see the corrected attached pdf for this).
I had some comments in the abstract before, and changes have been made, however, it is still not accurate enough. Please see the specific comments on the abstract added to the pdf revised version and make the corresponding changes. However, as a general comment on the abstract I want to highlight the fact that it barely deals with novel aspects of the paper. It does state that there are higher CBL heights coincident when there is stronger radiation, but that is a very well-known fact, so the authors should re-structure the abstract and stress more on what is actually a scientific novelty: the evaluation of the vertical velocity from the MMCR to investigate the CBL height. They should look into capabilities and limitations of this approach. And if it is capable of assessing diurnal and seasonal variabilities then say that, but do not state the sentences as if the novelty was that higher CBLHs correspond to higher radiation, because that is not a novelty.
In the methodology I had pointed out that the specifications of the radar were missing and still this is the case for some, as it is pointed out in the pdf, please check specific comments there.
In order to evaluate how well their vertical variance threshold methodology acts to estimate CBLH the authors compare with radiosonde at 0800 LT. This is valuable, however discussion is missing. Please answer these questions:
1. What does “generally consistent” (line 238) mean in terms of standard deviation? or some other objective quantification that you should utilize to quantitatively, statistically and significantly compare both methodologies.
2. How does the evolution of the diurnal cycle affects this comparison? At 8:00 am the convection in the ABL should be starting to take place, so this corresponds to a growing boundary layer phase, therefore it is a good time to estimate it with the variance as you do it, that makes sense and the utilization of radiosondes is also valuable. But you need to discuss that this is a phase in which CBL is growing and it will grow more during the diurnal cycle, however I assume that there are no later radiosondes to compare with a more developed boundary layer, which is ok but also needs to be stated.
3. Authors utilize now also the threshold of the bulk Richardson number to estimate a boundary layer height. This is a valuable methodology but needs to be much further described. The equation of the Richardson number is added in the answers but not in the paper, please add it to the paper and explain how the calculations were made. Furthermore, the difference between gradient and bulk Richardson number should be clear, the equation written in the answers is correct but the explanation lack the fact that the potential temperature at each height and at the surface is considered (difference with the surface and not a continuous derivative as in the gradient).
I had previously a comment on what do authors mean by “subsidence” and now they changed it to “dip” answering to my comment. However, they still did not explain what do they refer when they now use “dip” please explain. In my perspective this is even more unclear now. Therefore, it is highly recommended to be changed in the paper. I think that the authors mean that the CBL height reduces, but I am really not sure and it is not clear in the paper what they refer to nor if there would be a physical mechanism explaining this.
On line 151 you say: “...a maximum unambiguous velocity of...” and it is not clear if you are referring to an uncertainty of the velocity or what is it, please be more precise and use scientific vocabulary.

Referee Report: PDF

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ED: Publish subject to minor revisions (review by editor) (10 Jan 2025) by Geraint Vaughan

AR by Kaiming Huang on behalf of the Authors (18 Jan 2025) Author's response Author's tracked changes Manuscript

ED: Publish as is (27 Jan 2025) by Geraint Vaughan

AR by Kaiming Huang on behalf of the Authors (28 Jan 2025) Manuscript

Journal article(s) based on this preprint

20 Mar 2025

Technical note: Evolution of convective boundary layer height estimated by Ka-band continuous millimeter wave radar at Wuhan in central China

Zirui Zhang, Kaiming Huang, Fan Yi, Wei Cheng, Fuchao Liu, Jian Zhang, and Yue Jia

Atmos. Chem. Phys., 25, 3347–3361, https://doi.org/10.5194/acp-25-3347-2025,https://doi.org/10.5194/acp-25-3347-2025, 2025

Short summary

Zirui Zhang, Kaiming Huang, Fan Yi, Fuchao Liu, Jian Zhang, and Yue Jia

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The CBLH is related to our health due to its crucial role in pollutant dispersion. The vertical velocity from MMCR can capture the CBLH evolution, especially the initial stage of CBLH rise and the final stage of CBLH dissipation due to little blind range and less impact by residual layer, thus the MMCR observation can clearly identify the diurnal evolution of CBLH. The study shows that the CBLH has an obvious seasonal feature, and is affected by radiation, humidity, cloud and precipitation.


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