the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 15 May 2024
Measurement report: The promotion of low-level jet and thermal-effect on development of deep convective boundary layer at the southern edge of the Taklimakan Desert
Abstract. A vigorous development process of the deep convective boundary layer (CBL) was observed at the southern edge of the Taklimakan Desert on 6 June, 2022. Based on coherent Doppler wind lidar and ERA5 data, the formation mechanism of the deep CBL exceeding 5 km was well analyzed, which was mainly promoted by the low-level jet (LLJ) and thermal-effect. The LLJ has made sufficient momentum, energy and material preparations for the development of the deep CBL. Firstly, the cold downhill airflow of the Tibet Plateau leading to LLJ weakens the height and intensity of the temperature inversion layer, which reduces the energy demand for the broken of the IL. Secondly, the LLJ not only supplements the material and energy in the residual layer, but also suppresses the exchange with the lower atmosphere. In addition, the LLJ provides a driving force for the development of the deep CBL. In terms of thermal factors, the Tibet Plateau sensible heat driven air-pump and cold front transit provide additional impetus for the development of the deep CBL. Finally, the formation of deep CBL was catalyzed by the extreme thermal effects of the underlying surface, such as the furnace effect and the atmospheric superadiabatic expansion process. The study of the development of the deep CBL is important for revealing the land-air exchange process of momentum, energy, and material between the Taklimakan Desert and the Tibetan Plateau.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
(2941 KB)
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2024-1010', Anonymous Referee #1, 09 Jul 2024
This manuscript reports lidar observations of an event with CBL as deep as over 5 km at the southern edge of the Taklimakan Desert. ERA5 reanalysis data was used to analyze the responsible mechanisms, as complemented by a conceptual diagram. The presented case is interesting and fits the scope of ‘Measurement report’ in ACP. I believe this work may be published upon addressing the issues given below.
1. More discussions on the status of research on CBL should be given. Since this work aims to report an extreme CBL case, it is of necessity to give some background information on this point. For example, why the deep CBL is important? What are the known mechanisms contributing to deep CBL? Which knowledge gap that this study aims to address?
Some recent works have reported such deep CBL cases over this region. To what extent this work advances our understanding on the formation mechanism of deep CBL? This point will stand upon well addressing recent progresses regarding this topic.
Wang, M., Xu, X., Xu, H., Lenschow, D. H., Zhou, M., Zhang, J., & Wang, Y. (2019). Features of the deep atmospheric boundary layer over the Taklimakan Desert in the summertime and its influence on regional circulation. Journal of Geophysical Research: Atmospheres, 124(23), 12755-12772.
Xu, H., Wang, M., Wang, Y., & Cai, W. (2018). Performance of WRF large eddy simulations in modeling the convective boundary layer over the Taklimakan Desert, China. Journal of Meteorological Research, 32(6), 1011-1025.
Zhang, L., Zhang, H., Li, Q., Wei, W., Cai, X., Song, Y., ... & Zhou, C. (2022). Turbulent mechanisms for the deep convective boundary layer in the Taklimakan Desert. Geophysical Research Letters, 49(15), e2022GL099447.
Zhang, L., Zhang, H., Cai, X., Song, Y., Mamtimin, A., & He, Q. (2024). Physical mechanisms of deep convective boundary layer leading to dust emission in the Taklimakan Desert. Geophysical Research Letters, 51(10), e2024GL108521.
2. It is expected that the readers can reproduce your results after reading the Methods section, while the processing of lidar data is not adequately illustrated here.
3. The impact of clouds is not well discussed. The presence of clouds may partially block the solar radiation to surface. The observed clouds seem to be rather thin in Figure 3, and the vertical air motions of clouds are similar to the dust layer below. The discussion around P7L11 is rather vague.
4. Causality issue. One of the major conclusions is that LLJ plays an important role in forming deep CBL. I do see that the study site was in the LLJ region, however, I did not find strong evidence showing how LLJ contributes to the formation of deep CBL in section 4.1. At the very least, one may be convinced if you show the well correlated time series of LLJ and BLH. Therefore, I suggest the authors to reorganize this section, and discuss this point more concisely and logically.
5. From Fig.8b, it seems that the cold front is tangentially related to the deep CBL. Looking back to the discussion at P13L23, I am not sure how the processes could be interpretated from the figure given.
6. ACP usually has very good production team, but I would suggest to find a native speaker to improve the language issues. Some awkward expressions may be revised. For example,
P1L16, remove well
P1L17, awkward sentence
P2L16, rephrase ‘so that … round’
P2L17-L19. I do not see the connections among the three points.
P2L21-L27. You may introduce the advantages of Doppler lidar in deep CBL observations, instead of demonstrating the hardware design.
Citation: https://doi.org/10.5194/egusphere-2024-1010-RC1 - AC1: 'Reply on RC1', Lian Su, 01 Aug 2024
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RC2: 'Comment on egusphere-2024-1010', Anonymous Referee #2, 18 Jul 2024
This paper investigates the formation of a deep convective boundary layer on June 6, 2022, at the southern edge of the Taklimakan Desert and the northern foot of the Tibetan Plateau, using coherent Doppler wind lidar (CDWL) and ERA5 reanalysis data. The study reveals the critical role of low-level jets and thermal effects in the development of the boundary layer, providing significant scientific insights into the transport of dust aerosols and the thermodynamic processes of the atmospheric boundary layer. Overall, this paper is well-written, scientifically rigorous, and presents strong conclusions with high publication value. I recommend it for publication after some additional details and further analysis are addressed.
General comments:
1. The paper does not provide a detailed explanation of how the boundary layer height is estimated using Equation (1) in the methods section. It is recommended that the authors provide a more detailed explanation of how the boundary layer height is derived.
2. The paper mentions the impact of the downhill airflow on the low-level jet and the inversion layer but lacks specific observational data and analysis. On page 5, line 21, the paper states: "At 0:00 LT~6:00 LT, before the formation of the LLJ, the downhill airflow blowing from the TP to the desert was superimposed on the desert background wind field." However, Figure 3e shows that the region is dominated by north and northeast winds, suggesting that the descending airflow is likely not from the Tibetan Plateau. Additionally, based on Figure 4, I believe that the local temperature drop is more likely due to the transport of cooler air from the upstream of the jet stream. It is recommended that the authors provide more information on the downhill airflow to make it easier for readers to understand.
3. The paper mentions that dust aerosols have an impact on surface and atmospheric temperatures but lacks specific quantitative analysis. Providing the diurnal variation of dust concentration could more intuitively show the impact of dust concentration changes on the boundary layer.
4. An interesting phenomenon can be observed in Figure 2, where higher boundary layers occur more frequently in spring and summer. Therefore, are the effects of the low-level jet and thermal effects on the deep convective boundary layer proposed in this study seasonal? We look forward to the authors addressing this question in the discussion section.
Specific comments：
1. P1 The abbreviation IL in the abstract is not defined.
2. P2 L15 “However, since the study site of MinFeng is located in the convergence area of the strong east-west airflows in the TD, resulting in the land-air interaction in this area is particularly prominent, so that the area is in bad wind-sand activity all the year round”. Please update this sentence structure.
3. P10 L5-9 Why did the authors use sea level air pressure in the study? Sea level pressure is absent in TP and Taklimakan Desert due to the presence of terrain. Is it reasonable to use the difference in sea level pressure to analyze the formation of downhill air flow?
4. P12 The title of Figure 6 should be revised as “…… from 12:00 LT to 22:00 LT ……”
5. Figure 4, 6, 7: Wind vectors should be much clearer, especially its direction, which is more conducive to the analysis of dust transport direction.
Citation: https://doi.org/10.5194/egusphere-2024-1010-RC2 - AC2: 'Reply on RC2', Lian Su, 01 Aug 2024
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2024-1010', Anonymous Referee #1, 09 Jul 2024
This manuscript reports lidar observations of an event with CBL as deep as over 5 km at the southern edge of the Taklimakan Desert. ERA5 reanalysis data was used to analyze the responsible mechanisms, as complemented by a conceptual diagram. The presented case is interesting and fits the scope of ‘Measurement report’ in ACP. I believe this work may be published upon addressing the issues given below.
1. More discussions on the status of research on CBL should be given. Since this work aims to report an extreme CBL case, it is of necessity to give some background information on this point. For example, why the deep CBL is important? What are the known mechanisms contributing to deep CBL? Which knowledge gap that this study aims to address?
Some recent works have reported such deep CBL cases over this region. To what extent this work advances our understanding on the formation mechanism of deep CBL? This point will stand upon well addressing recent progresses regarding this topic.
Wang, M., Xu, X., Xu, H., Lenschow, D. H., Zhou, M., Zhang, J., & Wang, Y. (2019). Features of the deep atmospheric boundary layer over the Taklimakan Desert in the summertime and its influence on regional circulation. Journal of Geophysical Research: Atmospheres, 124(23), 12755-12772.
Xu, H., Wang, M., Wang, Y., & Cai, W. (2018). Performance of WRF large eddy simulations in modeling the convective boundary layer over the Taklimakan Desert, China. Journal of Meteorological Research, 32(6), 1011-1025.
Zhang, L., Zhang, H., Li, Q., Wei, W., Cai, X., Song, Y., ... & Zhou, C. (2022). Turbulent mechanisms for the deep convective boundary layer in the Taklimakan Desert. Geophysical Research Letters, 49(15), e2022GL099447.
Zhang, L., Zhang, H., Cai, X., Song, Y., Mamtimin, A., & He, Q. (2024). Physical mechanisms of deep convective boundary layer leading to dust emission in the Taklimakan Desert. Geophysical Research Letters, 51(10), e2024GL108521.
2. It is expected that the readers can reproduce your results after reading the Methods section, while the processing of lidar data is not adequately illustrated here.
3. The impact of clouds is not well discussed. The presence of clouds may partially block the solar radiation to surface. The observed clouds seem to be rather thin in Figure 3, and the vertical air motions of clouds are similar to the dust layer below. The discussion around P7L11 is rather vague.
4. Causality issue. One of the major conclusions is that LLJ plays an important role in forming deep CBL. I do see that the study site was in the LLJ region, however, I did not find strong evidence showing how LLJ contributes to the formation of deep CBL in section 4.1. At the very least, one may be convinced if you show the well correlated time series of LLJ and BLH. Therefore, I suggest the authors to reorganize this section, and discuss this point more concisely and logically.
5. From Fig.8b, it seems that the cold front is tangentially related to the deep CBL. Looking back to the discussion at P13L23, I am not sure how the processes could be interpretated from the figure given.
6. ACP usually has very good production team, but I would suggest to find a native speaker to improve the language issues. Some awkward expressions may be revised. For example,
P1L16, remove well
P1L17, awkward sentence
P2L16, rephrase ‘so that … round’
P2L17-L19. I do not see the connections among the three points.
P2L21-L27. You may introduce the advantages of Doppler lidar in deep CBL observations, instead of demonstrating the hardware design.
Citation: https://doi.org/10.5194/egusphere-2024-1010-RC1 - AC1: 'Reply on RC1', Lian Su, 01 Aug 2024
-
RC2: 'Comment on egusphere-2024-1010', Anonymous Referee #2, 18 Jul 2024
This paper investigates the formation of a deep convective boundary layer on June 6, 2022, at the southern edge of the Taklimakan Desert and the northern foot of the Tibetan Plateau, using coherent Doppler wind lidar (CDWL) and ERA5 reanalysis data. The study reveals the critical role of low-level jets and thermal effects in the development of the boundary layer, providing significant scientific insights into the transport of dust aerosols and the thermodynamic processes of the atmospheric boundary layer. Overall, this paper is well-written, scientifically rigorous, and presents strong conclusions with high publication value. I recommend it for publication after some additional details and further analysis are addressed.
General comments:
1. The paper does not provide a detailed explanation of how the boundary layer height is estimated using Equation (1) in the methods section. It is recommended that the authors provide a more detailed explanation of how the boundary layer height is derived.
2. The paper mentions the impact of the downhill airflow on the low-level jet and the inversion layer but lacks specific observational data and analysis. On page 5, line 21, the paper states: "At 0:00 LT~6:00 LT, before the formation of the LLJ, the downhill airflow blowing from the TP to the desert was superimposed on the desert background wind field." However, Figure 3e shows that the region is dominated by north and northeast winds, suggesting that the descending airflow is likely not from the Tibetan Plateau. Additionally, based on Figure 4, I believe that the local temperature drop is more likely due to the transport of cooler air from the upstream of the jet stream. It is recommended that the authors provide more information on the downhill airflow to make it easier for readers to understand.
3. The paper mentions that dust aerosols have an impact on surface and atmospheric temperatures but lacks specific quantitative analysis. Providing the diurnal variation of dust concentration could more intuitively show the impact of dust concentration changes on the boundary layer.
4. An interesting phenomenon can be observed in Figure 2, where higher boundary layers occur more frequently in spring and summer. Therefore, are the effects of the low-level jet and thermal effects on the deep convective boundary layer proposed in this study seasonal? We look forward to the authors addressing this question in the discussion section.
Specific comments：
1. P1 The abbreviation IL in the abstract is not defined.
2. P2 L15 “However, since the study site of MinFeng is located in the convergence area of the strong east-west airflows in the TD, resulting in the land-air interaction in this area is particularly prominent, so that the area is in bad wind-sand activity all the year round”. Please update this sentence structure.
3. P10 L5-9 Why did the authors use sea level air pressure in the study? Sea level pressure is absent in TP and Taklimakan Desert due to the presence of terrain. Is it reasonable to use the difference in sea level pressure to analyze the formation of downhill air flow?
4. P12 The title of Figure 6 should be revised as “…… from 12:00 LT to 22:00 LT ……”
5. Figure 4, 6, 7: Wind vectors should be much clearer, especially its direction, which is more conducive to the analysis of dust transport direction.
Citation: https://doi.org/10.5194/egusphere-2024-1010-RC2 - AC2: 'Reply on RC2', Lian Su, 01 Aug 2024
Peer review completion
Journal article(s) based on this preprint
Data sets
ERA5 data sets ECMWF https://cds.climate.copernicus.eu
deep_CBL_lidar_datas Lian Su https://figshare.com/articles/dataset/deep_CBL_lidar_datas/25434556
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Chunsong Lu
Jinlong Yuan
Xiaofei Wang
Qing He
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(2941 KB) - Metadata XML