the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
How do convective cold pools influence the boundary-layer atmosphere near two wind turbines in northern Germany?
Abstract. With increasing wind energy in the German energy grid, it is crucial to better understand how particular atmospheric phenomena can impact wind turbines and the surrounding boundary-layer atmosphere. Deep convection is one source of uncertainty for wind energy prediction, with the near-surface convective outflow (i.e., cold pool) causing rapid kinematic and thermodynamic changes that are not adequately captured by operational weather models. Using 1-minute meteorological mast and remote-sensing vertical profile observations from the WiValdi research wind park in northern Germany, we detect and characterize 120 convective cold pool passages over a period of 4 years in terms of their temporal evolution and vertical structure. We particularly focus on variations in wind-energy-relevant variables (wind speed and direction, turbulence strength, shear, veer and static stability) within the turbine rotor layer (34–150 m height) to isolate cold pool impacts that are critical for wind turbine operations. Near hub-height (92 m) during the gust front passage, there are relatively increased wind speeds up to +4 m s−1 in addition to the background flow, a relative wind direction shift up to +15°, and increased turbulence strength for a median cold pool. Given hub-height wind speeds lying within the partial load region of the power curve for the detected cases, there is an increase in estimated power of up to 50 % which lasts for 30 minutes. We find a ’nose shape’ in relative wind speeds and θv at hub-height during gust front passages, with larger wind direction changes closer to the surface. This manifests as asymmetric fluctuations in positive shear, negative veer, and stability across the rotor layer, with relative variations below hub-height at least twice as large compared with above hub-height and temporarily opposite signs for stability that have complex implications for turbine wakes. Doppler wind lidar profiles indicate that kinematic changes associated with the gust front extend to a height of 650–700 m, providing an estimate for cold pool depth and highlighting that cold pool impacts would typically extend beyond the height of current wind turbines. After the cold pool gust front passage, there is gradually increasing stability, with a decrease in θv to -2 K, a gradual decrease in turbulence strength, and faster recovery of wind speed than wind direction.
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RC1: 'Comment on wes-2025-38', Anonymous Referee #1, 07 May 2025
The manuscript “How do convective cold pools influence the boundary-layer atmosphere near two wind turbines in northern Germany?” addresses a timely and relevant topic which bridges atmospheric sciences with wind energy: convective cold pools (CPs). The downdrafts produced by convective rain have acquired renewed interest in the last 3-4 years, with several observational studies published characterizing composites of CPs from meteorological tower measurements, and from networks of ground-based weather stations in Northern Europe. This study by Thayer et al. is the first to my knowledge that focuses on the characteristics of CPs specifically in regards to the effect on wind turbines (in the context of the WiValdi test site), focusing on the heights where the rotor is located. The data is new, the text is very clear, the methods sound, and the figures explicative. I find this work ready to be published, after taking into consideration minor comments. I have included a pdf with the specific comments.
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RC2: 'Comment on wes-2025-38', Anonymous Referee #2, 12 May 2025
General Comments:
The manuscript entitled "How do convective cold pools influence the boundary-layer atmosphere near two wind turbines in northern Germany?" by Jeffrey D. Thayer and co-authors studies the statistical footprint of convectively induced cold-air outflows on thermodynamic and dynamical properties of the atmospheric boundary layer at a research wind park in northern Germany. By applying a custom detection algorithm and analyzing meteorological in-situ and remote-sensing observations, the authors characterize the temperature, humidity, and wind signals of 120 cold-pool passages within the rotor layer of wind turbines. Their findings suggest that cold pools can temporarily increase wind energy output by up to 50 %, whereas the associated wind fluctuations vary asymmetrically across the rotor layer and the increased near-surface static stability could impact the turbulence in the wakes of a wind turbine.
Overall, the manuscript is well-written, clearly structured, and guides the reader well through the different parts of the study. In the introduction, the current state of knowledge on this relevant and timely topic as well as the new contribution of the study are clearly outlined. The used experimental setup and analysis methods are described in a mostly understandable and transparent way. Although the results part covers several aspects of this research topic, it is presented in a balanced way and does not become lengthy. Moreover, the results are always discussed in the context of the current literature. The only criticism I could make is that I feel that the study could have gone a step further and be clearer on possible implications of the results for wind energy applications, which would support the significance of this work even further. Nevertheless, my overall assessment of this study is very positive and after addressing the minor comments listed below, I am happy to recommend the manuscript for publication in WES.
Specific Comments:
- Title: I suggest to use the more common term "atmospheric boundary layer" instead of "boundary-layer atmosphere"
- Line 13: Please introduce Theta_v
- L14: I would go with the term "static stability"
- L19: Please clarify that the -2 K cooling refers to the near surface conditions
- L46: "Limited work" by itself does not define a scientific gap in literature. What exactly do the existing studies miss?
- L49: "Rarely": See previous comment.
- L103: Name the measurement heights of the mast since these are visualized e.g. in Fig. 7
- L104: How high are the three meteorological masts?
- Fig. 1a: I suggest adding the locations of some major cities and a distance scale for reference.
- Fig. 1b: I would also mention in the text that the position of the MWR and lidar has changed over time.
- L129: For clarity, I suggest to mention that the microwave radiometer is a passive instrument.
- L151: Please introduce Theta_v
- L161: What does "positive daily wind anomaly" mean? Does this refer to the maximum wind speed of the day, a positive anomaly relative to the daily mean wind speed, or something else?
- L172: Both Kruse et al. (2022) and Kirsch et al. (2021) use a 20-minute period to detect temperature drops related to cold pool passages.
- L175: Can you specify "at least somewhat"?
- Section 3: As this section is rather long, I suggest to introduce sub-sections for a clearer structure.
- L209: Please specify the exact time period instead of only the years.
- Table 1: Why does the table only show the pre-event data? I think that listing the actual cold pool signals would be more instructive for the reader.
- Table 1: Does the measurement accuracy of the instrument allow to show the data with a two-digit accuracy?
- L218: What is the median temperature decrease over the cases? Here, showing the corresponding data in Table 1 would help (see earlier comment).
- Figure 2: The differently colored dots and outlines are very hard to see in the plots.
- L267-269: Are these measurements taken at the inflow mast? This is relevant for the interpretation of the results and could also be clarified elsewhere.
- Fig. 4: I assume that the central lines show the respective median but this is not indicated in the figure caption.
- L290-291: The median temperature evolution at 85 m (Fig. 4d) shows a slightly weaker signal than near the surface (Fig. 3). It might be worth mentioning that this is consistent with previous studies (e.g. Kirsch et al., 2021).
- L294-305: This paragraph feels a bit disconnected from the rest of the section. I am not entirely sure that the purpose of the case study is, apart from demonstrating that the composite properties of a cold pool also materialize in a single case. If the authors decide to keep the case study, I suggest to move it to an earlier location in the section, maybe in connection with Fig. 2.
- L312: I would say that the wind speed perturbation reaches up to 800 m rather than 650 m.
- L336: I am not convinced by this argument. I am inclined to think that the "nose" in the profile a hub height points to an impact of the rotor itself, but I can only guess what process causes this profile. This would be very interesting to know but probably involves some speculation.
- L344-345: Could this be caused by different adjustment times of the temperature sensors between surface and mast (if the sensors are different)?
- L400: Since section 6 mostly summarizes the methods and findings of the study, I suggest to call it "Summary & Conclusions"
- 470-472: I find the closing statement of the study rather weak. I would hope for more concrete implications for the wind energy applications to increase the significance of this timely and relevant study. Moreover, the authors could clarify what is exactly the benefit of an larger experimental setup compared to the current one.
Technical Corrections:
- L102: Add space in "4.3 D"
- L190: What does "WN" mean?
- L267: Add space in "subrange of"
- Figs. 4, 5, 7, 8, 9: I suggest moving the labels a) to d) to the top left corner of the subplots for consistency.
- L373: Add space in "cut-out hub-height"
Citation: https://doi.org/10.5194/wes-2025-38-RC2
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