Effects of Mesoscale Surface Thermal Heterogeneity on Low-Level Horizontal Wind Speeds

Kang, Song‐Lak; Lenschow, Donald H.; Sullivan, Peter P.

doi:10.1007/s10546-011-9691-4

Cited by 15 publications

(14 citation statements)

References 52 publications

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“…The biases and 62s bounds (95% confidence intervals; s is standard deviation) are 20.9 6 0.18, 21.0 6 0.18, and 20.8 6 0.18 m s 21 for S MYJ , S UW , and S YSU , respectively. The larger ramp frequency in March-June when compared with winter likely results from ramps associated with non-synoptic-scale forcing, such as lower-atmosphere or local-surface thermal heterogeneity (Kang et al 2012). As shown in Fig.…”

Section: A Evaluation Of Mean Wind Predictionsmentioning

confidence: 94%

Evaluation of WRF-Predicted Near-Hub-Height Winds and Ramp Events over a Pacific Northwest Site with Complex Terrain

Yang

Berg

Pekour

et al. 2013

Journal of Applied Meteorology and Climatology

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One challenge with wind-power forecasts is the accurate prediction of rapid changes in wind speed (ramps). To evaluate the Weather Research and Forecasting (WRF) model's ability to predict such events, model simulations, conducted over an area of complex terrain in May 2011, are used. The sensitivity of the model's performance to the choice among three planetary boundary layer (PBL) schemes [Mellor-Yamada-Janji c (MYJ), University of Washington (UW), and Yonsei University (YSU)] is investigated. The simulated nearhub-height winds (62 m), vertical wind speed profiles, and ramps are evaluated against measurements obtained from tower-mounted anemometers, a Doppler sodar, and a radar wind profiler deployed during the Columbia Basin Wind Energy Study (CBWES). The predicted winds at near-hub height have nonnegligible biases in monthly mean under stable conditions. Under stable conditions, the simulation with the UW scheme better predicts upward ramps and the MYJ scheme is the most successful in simulating downward ramps. Under unstable conditions, simulations using the YSU and UW schemes show good performance in predicting upward ramps and downward ramps, with the YSU scheme being slightly better at predicting ramps with durations longer than 1 h. The largest differences in mean wind speed profiles among simulations using the three PBL schemes occur during upward ramps under stable conditions, which were frequently associated with low-level jets. The UW scheme has the best overall performance in ramp prediction over the CBWES site when evaluated using prediction accuracy and capture-rate statistics, but no single PBL parameterization is clearly superior to the others when all atmospheric conditions are considered.

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Section: A Evaluation Of Mean Wind Predictionsmentioning

confidence: 94%

Evaluation of WRF-Predicted Near-Hub-Height Winds and Ramp Events over a Pacific Northwest Site with Complex Terrain

Yang

Berg

Pekour

et al. 2013

Journal of Applied Meteorology and Climatology

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“…Here we use the numerical model "Cloud Model version 1" (CM1) that has been used for several LES studies in recent years (e.g., Kang and Bryan 2011;Kang et al 2012;Wang 2014;Nowotarski et al 2014;Markowski and Bryan 2016). Details of the model used here, including a new "two part" subgrid model near the surface, are provided in the Appendix.…”

Section: Large-eddy Simulationsmentioning

confidence: 99%

A Simple Method for Simulating Wind Profiles in the Boundary Layer of Tropical Cyclones

Bryan

Worsnop

Lundquist

et al. 2016

Boundary-Layer Meteorol

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A method to simulate characteristics of wind speed in the boundary layer of tropical cyclones in an idealized manner is developed and evaluated. The method can be used in a single-column modelling set-up with a planetary boundary-layer parametrization, or within large-eddy simulations (LES). The key step is to include terms in the horizontal velocity equations representing advection and centrifugal acceleration in tropical cyclones that occurs on scales larger than the domain size. Compared to other recently developed methods, which require two input parameters (a reference wind speed, and radius from the centre of a tropical cyclone) this new method also requires a third input parameter: the radial gradient of reference wind speed. With the new method, simulated wind profiles are similar to composite profiles from dropsonde observations; in contrast, a classic Ekman-type method tends to overpredict inflow-layer depth and magnitude, and two recently developed methods for tropical cyclone environments tend to overpredict near-surface wind speed. When used in LES, the new technique produces vertical profiles of total turbulent stress and estimated eddy viscosity that are similar to values determined from low-level aircraft flights in tropical cyclones. Temporal spectra from LES produce an inertial subrange for frequencies 0.1 Hz, but only when the horizontal grid spacing 20 m.

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“…On the other hand, the SC advects air parcels from the cold towards the warm patch which are on average cooler than the surrounding air (see Fig. 1), stabilizing the lower CBL over the warm patch, as shown by Kang and Davis (2008) and Kang et al (2012). For the A20L32* simulation we suppose that the stabilization is the governing mechanism reducing entrainment over the warm patch, whereas e.g.…”

Section: What Causes the Reduced Entrainment For Small Heterogeneity mentioning

confidence: 99%

On the Effect of Surface Heat-Flux Heterogeneities on the Mixed-Layer-Top Entrainment

Sühring

Maronga

Herbort

et al. 2014

Boundary-Layer Meteorol

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We used a set of large-eddy simulations to investigate the effect of one-dimensional stripe-like surface heat-flux heterogeneities on mixed-layer top entrainment. The profiles of sensible heat flux and the temporal evolution of the boundary-layer depth revealed decreased entrainment for small heat-flux amplitudes and increased entrainment for large heat-flux amplitudes, compared to the homogeneously-heated mixed layer. For large heat-flux amplitudes the largest entrainment was observed for patch sizes in the order of the boundary-layer depth, while for significantly smaller or larger patch sizes entrainment was similar as in the homogeneous case. In order to understand the underlying physics of this impact, a new approach was developed to infer local information on entrainment by means of the local flux divergence. We found an entrainment maximum over the centre of the stronger heated surface patch, where thermal energy is accumulated by the secondary circulation (SC) that was induced by the surface heterogeneity. Furthermore, we observed an entrainment maximum over the less heated patch as well, which we suppose is to be linked to the SC-induced horizontal flow convergence at the top of the convective boundary layer (CBL). For small heat-flux amplitudes a counteracting effect dominates that decreases entrainment, which we suppose is the horizontal advection of cold air in the lower, and warm air in the upper, CBL by the SC, stabilizing the CBL and thus weakening thermal convection. Moreover, we found that a mean wind can reduce the heterogeneity-induced impact on entrainment. If the flow is aligned perpendicular to the border between the differentially-heated patches, the SC and thus its impact on entrainment vanishes due to increased horizontal mixing, even for moderate wind speeds. However, if the flow is directed parallel to the border between the differentially-heated patches, the SC and thus its impact on entrainment persists.

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Effects of Mesoscale Surface Thermal Heterogeneity on Low-Level Horizontal Wind Speeds

Cited by 15 publications

References 52 publications

Evaluation of WRF-Predicted Near-Hub-Height Winds and Ramp Events over a Pacific Northwest Site with Complex Terrain

Evaluation of WRF-Predicted Near-Hub-Height Winds and Ramp Events over a Pacific Northwest Site with Complex Terrain

A Simple Method for Simulating Wind Profiles in the Boundary Layer of Tropical Cyclones

On the Effect of Surface Heat-Flux Heterogeneities on the Mixed-Layer-Top Entrainment

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