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Abstract Unsteadiness and horizontal heterogeneities frequently characterize atmospheric motions, especially within convective storms, which are frequently studied using large-eddy simulations (LES). The models of near-surface turbulence employed by atmospheric LES, however, predominantly assume statistically steady and horizontally homogeneous conditions (known as the equilibrium approach). The primary objective of this work is to investigate the potential consequences of such unrealistic assumptions in simulations of tornadoes. Cloud Model 1 (CM1) LES runs are performed using three approaches to model near-surface turbulence: the “semi-slip” boundary condition (which is the most commonly used equilibrium approach), a recently proposed nonequilibrium approach that accounts for some of the effects of turbulence memory, and a nonequilibrium approach based on thin boundary layer equations (TBLE) originally proposed by the engineering community for smooth-wall boundary layer applications. To be adopted for atmospheric applications, the TBLE approach is modified to account for the surface roughness. The implementation of TBLE into CM1 is evaluated using LES results of an idealized, neutral atmospheric boundary layer. LES runs are then performed for an idealized tornado characterized by rapid evolution, strongly curved air parcel trajectories, and substantial horizontal heterogeneities. The semi-slip boundary condition, by design, always yields a surface shear stress opposite the horizontal wind at the lowest LES grid level. The nonequilibrium approaches of modeling near-surface turbulence allow for a range of surface-shear-stress directions and enhance the resolved turbulence and wind gusts. The TBLE approach even occasionally permits kinetic energy backscatter from unresolved to resolved scales. Significance Statement The traditional approach of modeling the near-surface turbulence is not suitable for a tornado characterized by rapid evolution, strongly curved air parcel trajectories, and substantial horizontal heterogeneities. To understand the influence of statistically unsteady and horizontally heterogeneous near-surface conditions on tornadoes, this work adopts a fairly sophisticated approach from the engineering community and implements it into a widely used atmospheric model with necessary modifications. Compared to the traditional approach, the newly implemented approach produces more turbulent near-surface winds, more flexible surface-drag directions, and stronger wind gusts. These findings suggest a simulated tornado is very sensitive to the modeling approach of near-surface turbulence.
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This content will become publicly available on August 16, 2026
Evaluating WRF Multiscale Wind Simulations in Complex Terrain: Insights From the Perdigão Field Campaign
Abstract Accurate microscale flow simulations are essential for assessing wind characteristics in complex terrain. This study evaluates a large ensemble of multiscale simulations, including large‐eddy simulations (LES), using the Weather Research and Forecasting model (WRF) over Perdigão, Portugal, driven by boundary conditions from multiple global data sets. Simulations are compared with data from the Perdigão field campaign, including radiosonde and flux tower measurements. Results show that LES, using high‐resolution topography and land use data, better replicate flow features and dynamics, providing valuable insights for wind resource quantification and mapping. We identify that model performance varies spatially. The RMSE of wind speed at 10 m at ridge towers is 5.65 m , while at valley towers, it is lower (2.28 m ), and variation across runs is greater for higher wind speeds. Temporally, surface winds show substantial variability throughout the day, posing greater modeling challenges during nighttime and synoptic transitions. This variability is not observed at 100 m, where topographic effects are less dominant and RMSE remains consistent across runs. Simulations driven by hourly boundary conditions perform best. However, drawing general conclusions about optimal turbulence modeling in the gray zone remains challenging due to microscale meteorology in complex terrain. Wind field characteristics are sensitive to turbulence scheme choice, particularly in the boundary layer, while above it, wind behavior is mainly influenced by boundary conditions. These results help identify key factors driving model variability and biases, which may guide future model developments to enhance wind flow simulation accuracy and reliability.
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- Award ID(s):
- 2236504
- PAR ID:
- 10653225
- Publisher / Repository:
- AGU
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 130
- Issue:
- 15
- ISSN:
- 2169-897X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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