the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 07 Jul 2023
Tropical cyclone low-level wind speed, shear, and veer: sensitivity to the boundary layer parameterization in WRF
Abstract. Mesoscale modeling can be used to analyze key parameters for wind turbine load assessment in a large variety of tropical cyclones. However, the modeled wind structure of tropical cyclones is known to be sensitive to the boundary layer scheme. We analyze modeled wind speed, shear, and wind veer across a wind turbine rotor plane in the eyewall and rainband region. We further assess the sensitivity of wind speed, shear, and veer to the boundary layer parameterization. Three model realizations of typhoon Megi over the open ocean using three frequently used boundary layer schemes in the Weather Research and Forecasting model are analyzed. All three typhoon simulations reasonably reproduce the cyclone track and structure. The boundary layer parametrization causes up to 21 % differences in median hub height wind speed between the simulations. The simulated wind speed variability is further dependent on the boundary layer scheme. The modeled wind shear is smaller or equal to the current IEC standard regardless of the boundary layer scheme for the eyewall and rainband region. While the surface inflow angle is sensitive to the boundary layer simulation, wind veer in the lowest 400 m of the atmospheric boundary layer is less affected by the boundary layer parametrization. Simulated wind veer reaches values up to 1.8 × 10⁻² ° m ⁻¹ (1.1 × 10 ⁻² ° m ⁻¹) in the eyewall region (rainband region) and is relatively small compared to moderate wind speed regimes. On average, simulated wind speed shear and wind veer are highest in the eyewall region. Yet strong spatial organization of wind shear and veer along the rainbands may increase wind turbine loads, due to rapid coherent wind profile changes at the turbine location.
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Status: closed
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RC1: 'Comment on wes-2023-71', Anonymous Referee #1, 22 Jul 2023
- AC1: 'Reply on RC1 and RC2', Sara Müller, 24 Nov 2023
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RC2: 'Comment on wes-2023-71', Anonymous Referee #2, 20 Oct 2023
General comments
This manuscript presents a study of examining the sensitivity of low-level wind speed, shear, and veer of typhoon Megi simulated by WRF to three PBL schemes. The goal is to assess how tropical cyclone (TC) force winds affect the wind loading of turbines. The research is interesting and valuable to costal wind engineering. The topic is suitable for Wind Energy Science. The manuscript overall is well written and easy to follow. However, I have a few comments about the manuscript. The manuscript may be published after major revision.
Specific comments
1. How PBL schemes affect TC simulations is an old topic. It has been extensively investigated in the past. The three PBL schemes, namely, YSU, MYJ, and MYNN schemes, investigated in this study has been evaluated previously by other studies. For example, Zhu et al. (2013) investigated how these three schemes affect eyewall asymmetric structure and mesovortices of TCs. Recently, Ye et al. (2023) and Ye et al. (2023) also investigated the impact of vertical turbulent mixing parameterization on TC intensification. Although this manuscript focuses on the issues from the wind engineering perspective different from previous studies, it is important for the authors to do a thorough literature review on this topic, so that the readers know the background of this research and what’s new of this manuscript.
Zhu, P., K. Menelaou, Z.-D. Zhu, 2013: Impact of sub-grid scale verti cal turbulent mixing on eyewall asymmetric structures and mesovortices of hurric anes Quart. J. Roy. Meteor. Soc.,140, 416-438. DOI:10.1002/qj.2147.
Ye, L., Li Y. B., Zhu P., and Gao Z. Q., 2023: The effects of boundary layer vertical turbulent diffusivity on the tropical cyclone intensity, Atmos. Res., 295, 13pp, https://doi.org/10.1016/j.atmosres.2023.106994.
Ye, G., Zhang X., and H. Yu, 2023: Modifications to Three-Dimensional Turbulence Parameterization for Tropical Cyclone Simulation at Convection-Permitting Resolution, J. Adv. Mod. Earth Sys., 15(4), https://doi.org/10.1029/2022MS003530.
2. This manuscript aims to address the impact of TC force winds on the wind loading of turbines. Yet, the simulations and the analyses presented in the manuscript focus on the TC winds on the open ocean. One would wonder, why winds on the open ocean can affect the wind turbines on shore? It is the winds at landfall that matter to the turbines. But TC force winds at the open ocean and landfall can be substantially different because of the complicated surface conditions at the coast (e.g., land-ocean contrast, surface roughness, topography, etc.). In this regard, more justification is needed to explain why the open ocean wind matters to turbines on shore.
3. The similarity and difference among the three PBL schemes, YSU, MYJ, and MYNN, are not well summarized. Vertical turbulent mixing schemes can be grouped into three categories in terms of order of closure, local/non-local mixing, and consideration of dry/moist thermodynamics. YSU is a first-order K-closure “dry” scheme that is formulated using thermodynamic variables (e.g., potential temperature, water vapor mixing ratio) that are not conserved for moist reversible adiabatic processes. But it considers non-local mixing. MYJ is a 1.5-order local Turbulent kinetic energy (TKE) “dry” scheme that is also formulated using thermodynamic variables that are not conserved for moist reversible adiabatic processes. Like MYJ, MYNN is a 1.5-order local TKE scheme, but it is formulated with thermodynamic variables that are conserved for moist reversible adiabatic processes. Therefore, it includes the cloud effects on the TKE buoyancy production.
4. To evaluate the impact of TC winds on turbine wind loading, the authors divided the TC winds into two regimes, eyewall and rainband based on the radii to the storm center. It is unclear why the eyewall region is defined from 60 to 120 km in radius and rainband region is defined from 200 to 400 km. In fact, such definitions can cause problems in wind analyses performed in this study. As shown in Figure 6, the winds at the inner edge of the defined eyewall are much weaker (~15 – 25 m/s) than those at the outer edge of the eyewall. The former is in the same range as that of the rainband region. But according to the authors, the eyewall region is considered to be a high wind regime, then, what is purpose to include these low winds in a high wind regime? It does not address the problem raised in the paper but only creates a large spread for the eyewall regime (Fig. 7). The definition of rainband regime also has problems. As shown in Figures 5d, 5e, and 5f, the width of rainbands is actually very narrow. In-between the eyewall and rainbands are the non-convective moat, which has different characteristics from the convective eyewall and rainbands. The current definition of rainband region mixes up the convective rainbands and non-convective moat. Such mix-up will have a significant impact on the wind shear and veer analyses as it clearly shows in Figures 5e and 5f that the wind shear and veer in the convective rainbands are substantially different from those in the moat.
Here are my suggestions. Since the authors are interested in the winds in the lower part of the boundary layer, it’s better to classify the TC winds into three regimes: eyewall, moat, and rainbands. For the eyewall region, the authors may consider defining it based on the maximum wind speed and the associated radius of the maximum wind (RMW), say, [RMW-R1, RMW+R2] where winds are greater than 80% of maximum wind speed. As for the rainband region, the authors may consider defining it based on either vertical velocity or hydrometeor mixing ratio, i.e., |w|>wcrit or qh>qcrit. The rest area in the TC inner core can be grouped into the moat region.
5. The authors argue that in addition to the wind speed, wind shear and veer are also important to turbine wind loading. But only the vertical profiles of wind speed in the defined eyewall and rainband regions are shown (Fig. 7). Then, what about the wind shear and veer. In fact, vertical profiles of wind speed in TCs have been shown in many papers, but not the shear and veer. So, it would be interesting to see what the vertical profiles of wind shear and veer in different regimes of a TC look like.
Citation: https://doi.org/10.5194/wes-2023-71-RC2 - AC1: 'Reply on RC1 and RC2', Sara Müller, 24 Nov 2023
Status: closed
-
RC1: 'Comment on wes-2023-71', Anonymous Referee #1, 22 Jul 2023
- AC1: 'Reply on RC1 and RC2', Sara Müller, 24 Nov 2023
-
RC2: 'Comment on wes-2023-71', Anonymous Referee #2, 20 Oct 2023
General comments
This manuscript presents a study of examining the sensitivity of low-level wind speed, shear, and veer of typhoon Megi simulated by WRF to three PBL schemes. The goal is to assess how tropical cyclone (TC) force winds affect the wind loading of turbines. The research is interesting and valuable to costal wind engineering. The topic is suitable for Wind Energy Science. The manuscript overall is well written and easy to follow. However, I have a few comments about the manuscript. The manuscript may be published after major revision.
Specific comments
1. How PBL schemes affect TC simulations is an old topic. It has been extensively investigated in the past. The three PBL schemes, namely, YSU, MYJ, and MYNN schemes, investigated in this study has been evaluated previously by other studies. For example, Zhu et al. (2013) investigated how these three schemes affect eyewall asymmetric structure and mesovortices of TCs. Recently, Ye et al. (2023) and Ye et al. (2023) also investigated the impact of vertical turbulent mixing parameterization on TC intensification. Although this manuscript focuses on the issues from the wind engineering perspective different from previous studies, it is important for the authors to do a thorough literature review on this topic, so that the readers know the background of this research and what’s new of this manuscript.
Zhu, P., K. Menelaou, Z.-D. Zhu, 2013: Impact of sub-grid scale verti cal turbulent mixing on eyewall asymmetric structures and mesovortices of hurric anes Quart. J. Roy. Meteor. Soc.,140, 416-438. DOI:10.1002/qj.2147.
Ye, L., Li Y. B., Zhu P., and Gao Z. Q., 2023: The effects of boundary layer vertical turbulent diffusivity on the tropical cyclone intensity, Atmos. Res., 295, 13pp, https://doi.org/10.1016/j.atmosres.2023.106994.
Ye, G., Zhang X., and H. Yu, 2023: Modifications to Three-Dimensional Turbulence Parameterization for Tropical Cyclone Simulation at Convection-Permitting Resolution, J. Adv. Mod. Earth Sys., 15(4), https://doi.org/10.1029/2022MS003530.
2. This manuscript aims to address the impact of TC force winds on the wind loading of turbines. Yet, the simulations and the analyses presented in the manuscript focus on the TC winds on the open ocean. One would wonder, why winds on the open ocean can affect the wind turbines on shore? It is the winds at landfall that matter to the turbines. But TC force winds at the open ocean and landfall can be substantially different because of the complicated surface conditions at the coast (e.g., land-ocean contrast, surface roughness, topography, etc.). In this regard, more justification is needed to explain why the open ocean wind matters to turbines on shore.
3. The similarity and difference among the three PBL schemes, YSU, MYJ, and MYNN, are not well summarized. Vertical turbulent mixing schemes can be grouped into three categories in terms of order of closure, local/non-local mixing, and consideration of dry/moist thermodynamics. YSU is a first-order K-closure “dry” scheme that is formulated using thermodynamic variables (e.g., potential temperature, water vapor mixing ratio) that are not conserved for moist reversible adiabatic processes. But it considers non-local mixing. MYJ is a 1.5-order local Turbulent kinetic energy (TKE) “dry” scheme that is also formulated using thermodynamic variables that are not conserved for moist reversible adiabatic processes. Like MYJ, MYNN is a 1.5-order local TKE scheme, but it is formulated with thermodynamic variables that are conserved for moist reversible adiabatic processes. Therefore, it includes the cloud effects on the TKE buoyancy production.
4. To evaluate the impact of TC winds on turbine wind loading, the authors divided the TC winds into two regimes, eyewall and rainband based on the radii to the storm center. It is unclear why the eyewall region is defined from 60 to 120 km in radius and rainband region is defined from 200 to 400 km. In fact, such definitions can cause problems in wind analyses performed in this study. As shown in Figure 6, the winds at the inner edge of the defined eyewall are much weaker (~15 – 25 m/s) than those at the outer edge of the eyewall. The former is in the same range as that of the rainband region. But according to the authors, the eyewall region is considered to be a high wind regime, then, what is purpose to include these low winds in a high wind regime? It does not address the problem raised in the paper but only creates a large spread for the eyewall regime (Fig. 7). The definition of rainband regime also has problems. As shown in Figures 5d, 5e, and 5f, the width of rainbands is actually very narrow. In-between the eyewall and rainbands are the non-convective moat, which has different characteristics from the convective eyewall and rainbands. The current definition of rainband region mixes up the convective rainbands and non-convective moat. Such mix-up will have a significant impact on the wind shear and veer analyses as it clearly shows in Figures 5e and 5f that the wind shear and veer in the convective rainbands are substantially different from those in the moat.
Here are my suggestions. Since the authors are interested in the winds in the lower part of the boundary layer, it’s better to classify the TC winds into three regimes: eyewall, moat, and rainbands. For the eyewall region, the authors may consider defining it based on the maximum wind speed and the associated radius of the maximum wind (RMW), say, [RMW-R1, RMW+R2] where winds are greater than 80% of maximum wind speed. As for the rainband region, the authors may consider defining it based on either vertical velocity or hydrometeor mixing ratio, i.e., |w|>wcrit or qh>qcrit. The rest area in the TC inner core can be grouped into the moat region.
5. The authors argue that in addition to the wind speed, wind shear and veer are also important to turbine wind loading. But only the vertical profiles of wind speed in the defined eyewall and rainband regions are shown (Fig. 7). Then, what about the wind shear and veer. In fact, vertical profiles of wind speed in TCs have been shown in many papers, but not the shear and veer. So, it would be interesting to see what the vertical profiles of wind shear and veer in different regimes of a TC look like.
Citation: https://doi.org/10.5194/wes-2023-71-RC2 - AC1: 'Reply on RC1 and RC2', Sara Müller, 24 Nov 2023
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