Turbulence Statistics in WRF Hybrid LES model for Temperature and Momentum

Understanding variability in atmospheric momentum and temperature is critical in a rapidly

changing climate characterized by increasingly frequent extreme weather events. We use the

Weather Research and Forecasting (WRF) model, which incorporates a hybrid Large-Eddy Simula-

tion approach, to simulate the European summer heatwave of 2019. Through

a nested domain configuration at horizontal resolutions of 15km, 5km, 1km, 200m, and 67m, we

resolve horizontal length scales from 100m up to 3,000,000m. A scale-by-scale (SBS) analysis of the

evolution equations for kinetic energy, temperature, potential and moist potential temperature,

and other scalar variables is performed with probability density functions, structure functions,

and SBS budget equations. This approach quantifies variability and extreme-events

frequency, examines the transition from explicitly resolved motions to parameterized fluxes, and

traces the scaling from the buoyancy sub-range to the Rossby radius of deformation. We estimate

key physical length scales throughout the troposphere, the subgrid scales (Kolmogorov, Ozmidov,

and Taylor microscales) along with the resolved buoyancy and rotation scales, and study their

evolution alongside SBS budgets. Our study shows the buoyancy sub-range following Kolmogorov

statistics horizontally, and pressure transport dictating the spectrum above the buoyancy length

scale. The pressure transport is directly forced by radiative forcing (through temperature advec-

tion), directly linking meso-scale variability with greenhouse warming.