Where numerical weather prediction meets large‐eddy simulations in a convective boundary layer during the FESSTVaL field experiment

This study leverages the Field Experiment on Sub-mesoscale Spatio-Temporal Variability in Lindenberg (FESSTVaL), including comprehensive observations of the surface, atmospheric boundary layer (ABL), and clouds, to compare the performance of a numerical weather prediction (NWP) model at sub-km resolutions with traditional large-eddy simulations (LES). This comparison is both relevant and timely: as the typical grid spacings of both techniques are converging, so should their results if the LES is assumed to be a good virtual laboratory for the ABL and if NWP is resolving the turbulence well. The representative of NWP is the Icosahedral Nonhydrostatic (ICON) model run at horizontal resolutions ranging from 2.5 km to 78 m. The LES model MicroHH is run at resolutions from 75 m to 38 m. ICON is set up in a limited area with realistic boundary conditions and heterogeneous land surface, whereas the setup of MicroHH is doubly periodic above a homogeneous surface and flat terrain. We focus our comparison at a horizontal grid resolution of about 78 m, where the two models overlap. ICON can represent the ABL processes with high fidelity. It approaches the performance of the MicroHH-LES in representing surface turbulent and radiation fluxes due to better-resolved ABL dynamics, clouds, and land-surface properties at sub-km resolutions. ... mehrThe modeled turbulence shows good agreement with observations, highlighting the equal importance of resolved and subgrid turbulent mixing at sub-km resolutions. Our modeling setup also reproduces deep convective cold pools, although with only a qualitatively realistic onset and development. In addition to the FESSTVaL observations used here, extensive datasets are available for follow-up studies focusing on specific processes. The complete set of ICON simulations covers the intensive observation period between June 5 and July 5, 2021, and can be used in process studies as well as providing a benchmark for model development.