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

• Published in: Journal of advances in modeling earth systems Vol. 9; no. 3; pp. 1572 - 1594
• Main Authors: Muñoz‐Esparza, Domingo, Lundquist, Julie K., Sauer, Jeremy A., Kosović, Branko, Linn, Rodman R.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 01-07-2017; American Geophysical Union (AGU)
• Subjects: Atmospheric boundary layer; atmospheric boundary layers; Convection; Convective rolls; CWEX-13; Diurnal cycle; Earth Sciences; Eddies; ENVIRONMENTAL SCIENCES; Evolution; Fetch; Fluctuations; large-eddy simulation; LES atmospheric modeling; Lidar; Lidar measurements; Modelling; multiscale modeling; Perturbation method; Probability theory; Profiling; Resolution; Simulation; Turbulence; Variability; Velocity; Vertical wind shear; Vertical wind velocities; Weather forecasting; WIND ENERGY; Wind shear; WRF
• ISSN: 1942-2466; 1942-2466
• DOI: 10.1002/2017MS000960

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.
Key Points
Multiscale modeling of a real‐world diurnal cycle is presented for the first time, enabled by the generalized cell perturbation method
The multiscale simulations exhibited realistic atmospheric features not captured by the mesoscale model such as convective rolls, global intermittency, and intra‐hour variability
Diurnal evolution of turbulence was accurately simulated, with probability density functions of resolved turbulent velocity fluctuations nearly identical to CWEX‐13 lidar measurements