Surface drag scaling in truly neutral atmospheric boundary layer using Laboratory ideas and ideal WRF LES

Turbulent drag is one of the most essential parameters in any turbulent flow. Accurately estimating drag is challenging due to a sharp velocity gradient near the wall. An approach for the scaling of drag for the hydrodynamically smooth wall-bounded laboratory flows, such as zero pressure gradient (ZPG) Laboratory Turbulent Boundary Layers (TBLs), are derived in Dixit et al. (2020 & 2022), which is known as the asymptotic drag law or the –1/2 power law. TBLs can be considered a specific case of Atmospheric Boundary Layer (ABL) flows, which are exceedingly complex. Comparing an ABL to a Lab TBL, the Reynolds number of an ABL is very high. Also, the surface of the atmosphere is rough. Therefore, the ABL presents a unique opportunity to examine drag scaling of laboratory TBL relations across orders of magnitude range in Reynolds number. As stability plays a special role in the ABL, the near-neutral conditions of the ABL are closer to the Lab TBLs, i.e., the buoyancy flux at the surface is close to zero. Such conditions are challenging to find in ABLs. In recent years, WRF (Weather Research and Forecasting ) has emerged as a better tool to simulate atmospheric flow conditions. Ideal WRF LES(large eddy simulation) mimics the neutral ABLs. Within the WRF LES, the boundary layer can quickly grow in neutrally stratified fluid background conditions. Results suggest that the TBLs and ABLs both follow the same asymptotic drag law.