the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 19 Nov 2024
Operational wind plants increase planetary boundary layer height: An observational study
Abstract. As wind energy deployment grows, interactions between wind plants and the surrounding environment become more prevalent. The current investigation seeks to understand these interactions by characterizing the impact of wind plants on the planetary boundary layer height (PBLH), utilizing observations from the American WAKE ExperimeNt (AWAKEN) campaign. Given the ambiguity of the definition of PBLH under stable atmospheric conditions, where the impact of wind plants is expected to be strongest, a comparison of different methods for identifying PBLH is first conducted using data collected by multiple different instruments. Then, using one of these methods that is thermodynamic and another that is turbulence-based, the values of PBLH measured at spatially distributed sites are compared under a range of atmospheric conditions. Both methods show a clear increase in PBLH downstream of a wind plant for stable conditions. These impacts are strongest when the upstream PBLH is shallow (less than 0.25 km), with the thermodynamic method showing a PBLH increase of 33–39 % and the turbulence-based method showing a 141 % increase. At a site 20 km downstream of the wind plant, these effects are no longer observed, suggesting PBLH has recovered. The results of this investigation show that wind plants can modify the surrounding atmosphere, improving understanding of wind plant–atmosphere interaction that is crucial for model development and validation.
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RC1: 'Comment on wes-2024-148', Anonymous Referee #1, 21 Jan 2025
The manuscript presents new measurements from the AWAKEN campaign. This community campaign is crucial for the wind energy community and is unique in its measurement capabilities. This is a continuation of the Krishnamurthy et al. (2024) work, where additional technical details of the experiments are described. The present work reports measurements of the planetary boundary layer height at the WAKEN site from different wind directions. The measurements reveal that wind farms increase this boundary layer height.
* Line 6: "Then, using one of these methods that is thermodynamic and" --> Please mention the used method and why this method has been selected (in abstract and conclusion)
* Line 193: Please clarify this statement.
* Line 234: How is the "2K" selected? Are the results sensitive to this value?
* Line 235: "If no inversion layer meeting these criteria is identified." --> How often does this happen?
* Section 3.2:
Using the minimum in w^prime w^prime. Looking at the corresponding Figure 6, we could also consider the intersection between the behavior between 600 and 1000 meters (approximate constant) and the linear behavior between 300 and 600 meters. This would give a value closer to 600 meters compared to the present value closer to 800 meters. Different vertical bin sizes could also be used. The point is, would it be possible to give some indication of uncertainty in the obtained heights?
* Section 4.2 vs. Section 4.3: Is this essentially a different representation of the same data?
* Section 4.2 and Section 4.3: Can you document the different p values in a table to provide a better overview for the reader?
* Section 4.4 "Effects of upstream PBLH on wind plant impacts" --> In sections 4.2 and 4.3, the development of the PBLH is also discussed.
* line 447: is it PBLH or the stability of the boundary layer (title section 4.2)? Of course, both are correlated.
* line 463: Can you discuss the implications of the lidar blind spot for these measurements in more detail?
* line 510-520: How do the mentioned downstream distances compare to the wind farm size.Citation: https://doi.org/10.5194/wes-2024-148-RC1 -
RC2: 'Comment on wes-2024-148', Anonymous Referee #2, 10 Feb 2025
The manuscript presents an attempt to investigate the effect of operating wind power plants on the development of the planetary boundary layer height (PBLH) based on a network of advanced atmospheric remote sensing instrumentation during the AWAKEN field campaign. The manuscript is in general well written and structured, the applied methods are adequate for the investigations and properly described. Figures and tables are nicely formatted and relatively easy to read. The topic of a potential influence of wind power plants on PBLH fits well in the scope WES. Nevertheless, I have two comments and concerns that will require some major revisions of the presented manuscript.
Figure 2: although it is very nice to see that example, I really miss a statistical proof in form of profiles of average bias/RMSE over all the >200 profiles you assume to be valid and utilized in your investigations; in addition I would highly recommend to separate between convective and stable situations, because the temperature/humidity remote sensing by the passive radiometers should have rather different accuracies for ground based/ground near night-time inversions (for the stable cases) and the capping inversion on top of the CBL during convective conditions. This would also better reflect the fact that the daytime, convective PBLH (in BL meteorology often identified as z_i) and the PBLH in stable conditions (often denoted as h) are caused/influenced/determined by considerably different parameters and processes.
The main issue I have with the manuscript is that I am not convinced that it is the effect of the wind power plant (alone) that is triggering the lift in PBLH during stable conditions. The wind farms along the investigated transects are located along/across ridges in the terrain that have (at least what I can read out of the maps) elevations above the surrounding flats/valleys that are in the same order as the wind turbine heights, consequently the terrain roughness alone also might influence the PBLH downstream. Do you have any indications that could provide additional evidence that it is really (mainly) the presence of operating wind power plants that causes the lift in PBLH and not the pure presence of elevated terrain? Have there e.g. been situations with considerable wind speed where the wind farms have been shut down for some hours/days that could show that the farms not operating won’t give a corresponding increase in PBLH downstream? Or are there any fine-scale model simulations in the AWAKEN context available that could be used to shed more light on this potential issue? I am fully aware that it might not be possible to revoke my concern based on the actually available data, but in this case the issue should at least be discussed in the introduction and during the presentation of the results. And maybe the corresponding conclusions should also be formulated a bit more carefully “strong evidence that wind plants can modify….. “ (line 515)
Here some additional minor comments and suggestions:
In general: “wind plant” is for me a rather unusual expression in wind energy meteorology, I would suggest to replace it by “wind power plant” and maybe even introduce an abbreviation (WPP?) as you use this expression quite a lot
Line 6: “multiple different instruments” sounds a bit strange/weird; maybe enough with just “multiple instruments”; if you want to specify “different” in more detail you should spend another sentence with a few wore details on it
Line 145: is it really correct that the vertical resolution is 2 km at 1 km above the ground? If so, how could this in any way be useful for BL studies, in particular in defining a reliable value of the BL height?
Line 178: please detail how you calculated/determined this scan specific threshold
Section 3.1.: I miss some more central references on the different methods to derive PBLH, in particular prior work in comparing different methods
Line 232: I don’t get the meaning of “land-locked”
Figure 4: as suggested before, I would plot this separately for the stable and convective situations
Lines 273/274: you should also mention buoyancy production here in this context.
References:
Here there are numerous inconsistencies with respect to abbreviating journal names, the missing of upper case in journal names, the presentation of doi, and some reference incompleteness
- Acevedo (line 557): journal name lower case
- Baars (line 563): remove “Publication Title:”; journal name abbreviated
- Beck (line 568): journal name lower case
- Bodini (line 74): journal name abbreviated
- Cal (line 580): journal name lower case
- Dai (line 590): journal name abbreviated
- Delle (line 596): journal name abbreviated
- Duncan (line 600): journal name abbreviated
- Frandsen (line 612): remove “An International Journal for ……..”
- Hauke (line 623): journal name lower case
- Jozef (line 635): journal name abbreviated
- Krishnamurthy (line 645): journal name missing
- Lee (line 647): journal name abbreviated
- Li (line 663): journal name abbreviated
- Lu (line 671): journal name abbreviated
- Münkel (line 697): journal name lower case
- Neggers (line 604): journal name abbreviated
- Pichugina (line 713): journal name lower case
- Su (line 737): journal name abbreviated
- Tucker (line 740): journal name lower case
- Turner (line 743): journal name abbreviated
- Wu (line 760): journal name lower case
Citation: https://doi.org/10.5194/wes-2024-148-RC2 -
RC3: 'Comment on wes-2024-148', Anonymous Referee #3, 27 Feb 2025
Review of Operational wind plants increase planetary boundary layer height: An observational study by A. Abraham et al.
The study focuses on whether wind turbine operation modifies boundary layer heights downstream, as observed in the AWAKEN field campaign. It uses and compares multiple methods of determining PBL heights from multiple instruments.
The manuscript is well-structured, with clearly described methods suitable for the investigations. The figures and tables are well-formatted and easy to read. The impact of wind power plants on PBLH aligns with WES's scope. However, I am concerned about better substantiating the manuscript's conclusions.
By the end of filtering out all the available data, only a few samples remain, mainly when stability constraints are applied. I am satisfied with the statistical testing used to compare the means of upstream and downstream PBLH. However, I wonder whether other differences in terrain or mesoscale circulations could be causing the changes in PBLH, which are unrelated to the operation of the wind farms. There are two ways around this. (1) Find periods when the turbines are not operating and verify that the PBL is unchanged in those cases, or (2) find some NWP model output and verify that similar changes in PBLH are not seen in the base (no wind farm) simulations but do appear when the wind farms are included. I don't suggest that you do these runs, but many groups have already run simulations with and without wind farms for the AWAKEN region. The data might already be available in the DOE repository. Of course, (1) will be best, but it might be hard to find enough data. (2) is not proof, but it might substantiate your hypothesis.
I also have a few suggestions for improving the text and figures:
1. I find it strange to call wind farms "wind plants". I would suggest "wind power plants" or "wind farms". But this is just what I am used to.
2. L10-11 "At a site 20 km downstream of the wind plant, these effects are no longer observed, suggesting PBLH has recovered." It is a weird sentence. The PBL has recovered from what?
3. The last sentence of the abstract is very vague: "The results of this investigation show that wind plants can modify the surrounding atmosphere, improving understanding of wind plant–atmosphere interaction that is crucial for model development and validation." This is true for any study. Please be more specific.
4. L24-25: "Furthermore, wind plant wake effects are not vertically confined to the rotor area and can extend well into the planetary boundary layer, " wake effects are in the PBL, so the sentence does not make sense. Please rewrite.
5. L58-59: "The wind plant also lifted the nose height of the nocturnal low-level jet". Again, the wind farms don't lift anything. Please rewrite.
6. L66. "... used WRF with the Fitch..." to "... used the WRF model with the Fitch..."
7. Section 4.1. I am not sure you wrote at what height is the Obukhov length computed. Also, I would suggest that "The Obukhov length, L, is used to determine atmospheric stability. " is replaced by "The Obukhov length, L, is used to stratify the data by stability conditions."
8. In Figures 9, 10, 11, 12, and 17, it isn't easy to see how the distributions have changed. Please add some horizontal lines to make it easier.
9. The equation in L414 is very "ugly". Words are enough, and the equation can be removed.
Citation: https://doi.org/10.5194/wes-2024-148-RC3
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