Coupled mesoscale‐LES modeling of a diurnal cycle during the CWEX‐13 field campaign: From weather to boundary‐layer eddies

Abstract

Multiscale modeling of a diurnal cycle of real‐world conditions is presented for the first time, validated using data from the CWEX‐13 field experiment. Dynamical downscaling from synoptic‐scale down to resolved three‐dimensional eddies in the atmospheric boundary layer (ABL) was performed, spanning 4 orders of magnitude in horizontal grid resolution: from 111 km down to 8.2 m (30 m) in stable (convective) conditions. Computationally efficient mesoscale‐to‐microscale transition was made possible by the generalized cell perturbation method with time‐varying parameters derived from mesoscale forcing conditions, which substantially reduced the fetch to achieve fully developed turbulence. In addition, careful design of the simulations was made to inhibit the presence of under‐resolved convection at convection‐resolving mesoscale resolution and to ensure proper turbulence representation in stably‐stratified conditions. Comparison to in situ wind‐profiling lidar and near‐surface sonic anemometer measurements demonstrated the ability to reproduce the ABL structure throughout the entire diurnal cycle with a high degree of fidelity. The multiscale simulations exhibit realistic atmospheric features such as convective rolls and global intermittency. Also, the diurnal evolution of turbulence was accurately simulated, with probability density functions of resolved turbulent velocity fluctuations nearly identical to the lidar measurements. Explicit representation of turbulence in the stably‐stratified ABL was found to provide the right balance with larger scales, resulting in the development of intra‐hour variability as observed by the wind lidar; this variability was not captured by the mesoscale model. Moreover, multiscale simulations improved mean ABL characteristics such as horizontal velocity, vertical wind shear, and turbulence.

Evaluation of the wind farm parameterization in the Weather Research and Forecasting model (version 3.8.1) with meteorological and turbine power data

“…No major synoptic events affected the area during this period. Moreover, when the nearsurface flows are southerly, the WC and the surface flux station measure winds unaffected by wind turbines (Muñoz-Esparza et al, 2017). Additionally, no curtailment of wind turbines occurred and the instruments operated normally during the period, making these 4 days ideal for model verification.…”

“…This campaign was a component of the larger CWEX project, which explored the interactions of wind turbines with crops, surface fluxes, and near-surface flows in different atmospheric stability regimes in flat terrain (Rajewski et al, 2013). Research facilitated by the CWEX projects include diurnal changes in observed turbine wakes (Rhodes and Lundquist, 2013), turbine interactions with moisture and carbon dioxide fluxes , LES modelling of turbine wakes in changing stability regimes , nocturnal low-level jet (LLJ) occurrences (Vanderwende et al, 2015), diurnal changes of the microclimate near wind turbines (Rajewski et al, 2016), multiple-wake interactions (Bodini et al, 2017), the evolution of turbine wakes during the evening transition (Lee and Lundquist, 2017), and coupled mesoscalemicroscale modelling (Muñoz-Esparza et al, 2017).…”

Analysis of Different Gray Zone Treatments in WRF-LES Real Case Simulations

“…This result suggests that the GZ domain 10 is lacking energy for the three simulations, and that a better treatment of turbulence at this scale is needed as will be further discussed in Section 4.3. At the micro scale domain, the spectra are substantially more energetic at higher frequencies and exhibit the f −1 decay seen in Muñoz-Esparza et al (2017) for these frequencies, also exclusively in the nested LES domain.…”

“…Under the first coupling approach, the GZ is avoided but turbulence generation methods must still be applied to the meso scale fields before they can be used as driving inflow to LES (Haupt et al, 2015;Mirocha et al, 2013). Under the second coupling approach, an adequate treatment of GZ resolutions is required and may be achieved by developing more flexible parameterizations (Shin and Dudhia, 2016;Ito et al, 2015) or by avoiding the GZ domains altogether and relying on turbulence generation strategies alone to couple meso and micro scale domains (Muñoz-Esparza et al, 2017).…”

“…So far, these and other ABLPs expanded to accommodate GZ resolutions are limited to convective boundary layers (CBLs) and have mostly been 10 verified against reference idealized LES (e.g., Shin and Dudhia (2016); Ito et al (2015); Kitamura (2015); Honnert et al (2011)). The only existing work evaluating meso-micro coupled simulations with WRF for a real case avoided the GZ by using a high nesting ratio and going directly from the meso (1 km) to the micro scale (90 m) domain (Muñoz-Esparza et al, 2017).…”